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Diabetes Mellitus (DM)


Erika F. Brutsaert

, MD, New York Medical College

Last full review/revision Sep 2020| Content last modified Sep 2020
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Diabetes mellitus is impaired insulin secretion and variable degrees of peripheral insulin resistance leading to hyperglycemia. Early symptoms are related to hyperglycemia and include polydipsia, polyphagia, polyuria, and blurred vision. Later complications include vascular disease, peripheral neuropathy, nephropathy, and predisposition to infection. Diagnosis is by measuring plasma glucose. Treatment is diet, exercise, and drugs that reduce glucose levels, including insulin, oral antihyperglycemic drugs, and non-insulin injectable drugs. Complications can be delayed or prevented with adequate glycemic control; heart disease remains the leading cause of mortality in diabetes mellitus.

There are 2 main categories of diabetes mellitus (diabetes)

  • Type 1

  • Type 2

The two types of diabetes can be distinguished by a combination of features (see table General Characteristics of Types 1 and 2 Diabetes Mellitus). Terms that describe the age of onset (juvenile or adult) or type of treatment ( insulin- or non– insulin-dependent) are no longer accurate because of overlap in age groups and treatments between disease types.

Impaired glucose regulation (impaired glucose tolerance, or impaired fasting glucose—see table Diagnostic Criteria for Diabetes Mellitus and Impaired Glucose Regulation) is an intermediate, possibly transitional, state between normal glucose metabolism and diabetes mellitus that becomes more common with aging. It is a significant risk factor for diabetes and may be present for many years before onset of diabetes. It is associated with an increased risk of cardiovascular disease, but typical diabetic microvascular complications are not very common (albuminuria and/or retinopathy develop in 6 to 10%).


Years of poorly controlled hyperglycemia lead to multiple, primarily vascular complications that affect small vessels (microvascular), large vessels (macrovascular), or both. (For additional detail, see Complications of Diabetes Mellitus.)

Microvascular disease underlies 3 common and devastating manifestations of diabetes mellitus:

Microvascular disease may also impair skin healing, so that even minor breaks in skin integrity can develop into deeper ulcers and easily become infected, particularly in the lower extremities. Intensive control of plasma glucose can prevent or delay many of these complications but may not reverse them once established.

Macrovascular disease involves atherosclerosis of large vessels, which can lead to

Immune dysfunction is another major complication and develops from the direct effects of hyperglycemia on cellular immunity. Patients with diabetes mellitus are particularly susceptible to bacterial and fungal infections.

Etiology of Diabetes Mellitus

Type 1 diabetes

  • Insulin production absent because of autoimmune pancreatic beta-cell destruction

In type 1 diabetes mellitus (previously called juvenile-onset or insulin-dependent), insulin production is absent because of autoimmune pancreatic beta-cell destruction possibly triggered by an environmental exposure in genetically susceptible people. Destruction progresses subclinically over months or years until beta-cell mass decreases to the point that insulin concentrations are no longer adequate to control plasma glucose levels. Type 1 diabetes generally develops in childhood or adolescence and until recently was the most common form diagnosed before age 30; however, it can also develop in adults (latent autoimmune diabetes of adulthood, which often initially appears to be type 2 diabetes). Some cases of type 1 diabetes, particularly in nonwhite patients, do not appear to be autoimmune in nature and are considered idiopathic. Type 1 accounts for < 10% of all cases of diabetes mellitus.

The pathogenesis of the autoimmune beta-cell destruction involves incompletely understood interactions between susceptibility genes, autoantigens, and environmental factors.

Susceptibility genes include those within the major histocompatibility complex (MHC)—especially HLA-DR3,DQB1*0201 and HLA-DR4,DQB1*0302, which are present in > 90% of patients with type 1 diabetes mellitus—and those outside the MHC, which seem to regulate insulin production and processing and confer risk of diabetes mellitus in concert with MHC genes. Susceptibility genes are more common among some populations than among others and explain the higher prevalence of type 1 diabetes in some ethnic groups (Scandinavians, Sardinians).

Autoantigens include glutamic acid decarboxylase, insulin, proinsulin, insulinoma-associated protein, zinc transporter ZnT8, and other proteins in beta cells. It is thought that these proteins are exposed or released during normal beta-cell turnover or beta-cell injury (eg, due to infection), activating primarily a T cell‒mediated immune response resulting in beta-cell destruction (insulitis). Glucagon-secreting alpha cells remain unharmed. Antibodies to autoantigens, which can be detected in serum, seem to be a response to (not a cause of) beta-cell destruction.

Several viruses (including coxsackievirus, rubella virus, cytomegalovirus, Epstein-Barr virus, and retroviruses) have been linked to the onset of type 1 diabetes. Viruses may directly infect and destroy beta cells, or they may cause beta-cell destruction indirectly by exposing autoantigens, activating autoreactive lymphocytes, mimicking molecular sequences of autoantigens that stimulate an immune response (molecular mimicry), or other mechanisms.

Diet may also be a factor. Exposure of infants to dairy products (especially cow’s milk and the milk protein beta casein), high nitrates in drinking water, and low vitamin D consumption have been linked to increased risk of type 1 diabetes. Early (< 4 months) or late (> 7 months) exposure to gluten and cereals increases islet cell autoantibody production. Mechanisms for these associations are unclear.

Type 2 diabetes

  • Resistance to insulin

In type 2 diabetes mellitus (previously called adult-onset or non– insulin-dependent), insulin secretion is inadequate because patients have developed resistance to insulin. Hepatic insulin resistance leads to an inability to suppress hepatic glucose production, and peripheral insulin resistance impairs peripheral glucose uptake. This combination gives rise to fasting and postprandial hyperglycemia. Often insulin levels are very high, especially early in the disease. Later in the course of the disease, insulin production may fall, further exacerbating hyperglycemia.

The disease generally develops in adults and becomes more common with increasing age; up to one third of adults > age 65 have impaired glucose tolerance. In older adults, plasma glucose levels reach higher levels after eating than in younger adults, especially after meals with high carbohydrate loads. Glucose levels also take longer to return to normal, in part because of increased accumulation of visceral and abdominal fat and decreased muscle mass.

Type 2 diabetes is becoming increasingly common among children as childhood obesity has become epidemic. Over 90% of adults with diabetes have type 2 disease. There are clear genetic determinants, as evidenced by the high prevalence of the disease within ethnic groups (especially American Indians, Hispanics, and Asians) and in relatives of people with the disease. Although several genetic polymorphisms have been identified over the past several years, no single gene responsible for the most common forms of type 2 diabetes has been identified.

Pathogenesis is complex and incompletely understood. Hyperglycemia develops when insulin secretion can no longer compensate for insulin resistance. Although insulin resistance is characteristic in people with type 2 diabetes and those at risk of it, evidence also exists for beta-cell dysfunction and impaired insulin secretion, including impaired first-phase insulin secretion in response to IV glucose infusion, a loss of normally pulsatile insulin secretion, an increase in proinsulin secretion signaling impaired insulin processing, and an accumulation of islet amyloid polypeptide (a protein normally secreted with insulin). Hyperglycemia itself may impair insulin secretion, because high glucose levels desensitize beta cells, cause beta-cell dysfunction (glucose toxicity), or both. These changes typically take years to develop in the presence of insulin resistance.

Obesity and weight gain are important determinants of insulin resistance in type 2 diabetes. They have some genetic determinants but also reflect diet, exercise, and lifestyle. An inability to suppress lipolysis in adipose tissue increases plasma levels of free fatty acids that may impair insulin-stimulated glucose transport and muscle glycogen synthase activity. Adipose tissue also appears to function as an endocrine organ, releasing multiple factors (adipocytokines) that favorably (adiponectin) and adversely (tumor necrosis factor-alpha, interleukin-6, leptin, resistin) influence glucose metabolism. Intrauterine growth restriction and low birth weight have also been associated with insulin resistance in later life and may reflect adverse prenatal environmental influences on glucose metabolism.

Miscellaneous types of diabetes

Miscellaneous types of diabetes mellitus account for a small proportion of cases. Causes include

  • Genetic defects affecting beta-cell function, insulin action, and mitochondrial DNA (eg, maturity-onset diabetes of youth)

  • Conditions that affect the pancreas (eg, cystic fibrosis, pancreatitis, hemochromatosis, pancreatectomy)

  • Endocrinopathies (eg, Cushing syndrome, acromegaly)

  • Toxins (eg, the rodenticide pyriminyl)

  • Drugs, most notably glucocorticoids, beta-blockers, protease inhibitors, atypical antipsychotics, and therapeutic doses of niacin

Pregnancy causes some insulin resistance in all women, but only a few develop gestational diabetes.


General Characteristics of Types 1 and 2 Diabetes Mellitus


Type 1

Type 2

Age at onset

Most commonly < 30 years

Most commonly > 30 years

Associated obesity


Very common

Propensity to ketoacidosis requiring insulin treatment for control



Plasma levels of endogenous insulin

Extremely low to undetectable

Variable; may be low, normal, or elevated depending on degree of insulin resistance and insulin secretory defect

Twin concordance


> 90%

Associated with specific HLA-D antigens



Pancreatic autoantibodies at diagnosis

Yes, but may be absent


Islet pathology

Insulitis, selective loss of most beta cells

Smaller, normal-appearing islets; amyloid (amylin) deposition common

Prone to develop diabetic complications (retinopathy, nephropathy, neuropathy, atherosclerotic cardiovascular disease)



Hyperglycemia responds to oral antihyperglycemic drugs


Yes, initially in many patients

Symptoms and Signs of Diabetes Mellitus

The most common symptoms of diabetes mellitus are those of hyperglycemia. The mild hyperglycemia of early diabetes is often asymptomatic; therefore, diagnosis may be delayed for many years. More significant hyperglycemia causes glycosuria and thus an osmotic diuresis, leading to urinary frequency, polyuria, and polydipsia that may progress to orthostatic hypotension and dehydration. Severe dehydration causes weakness, fatigue, and mental status changes. Symptoms may come and go as plasma glucose levels fluctuate. Polyphagia may accompany symptoms of hyperglycemia but is not typically a primary patient concern. Hyperglycemia can also cause weight loss, nausea and vomiting, and blurred vision, and it may predispose to bacterial or fungal infections.

Patients with type 1 diabetes typically present with symptomatic hyperglycemia and sometimes with diabetic ketoacidosis (DKA). Some patients experience a long but transient phase of near-normal glucose levels after acute onset of the disease (honeymoon phase) due to partial recovery of insulin secretion.

Patients with type 2 diabetes may present with symptomatic hyperglycemia but are often asymptomatic, and their condition is detected only during routine testing. In some patients, initial symptoms are those of diabetic complications, suggesting that the disease has been present for some time. In some patients, hyperosmolar hyperglycemic state occurs initially, especially during a period of stress or when glucose metabolism is further impaired by drugs, such as corticosteroids.

Diagnosis of Diabetes Mellitus

  • Fasting plasma glucose (FPG) levels

  • Glycosylated hemoglobin (HbA1C)

  • Sometimes oral glucose tolerance testing

Diabetes mellitus is indicated by typical symptoms and signs and confirmed by measurement of plasma glucose (1). Measurement after an 8- to 12-hour fast (FPG) or 2 hours after ingestion of a concentrated glucose solution (oral glucose tolerance testing [OGTT]) is best (see table Diagnostic Criteria for Diabetes Mellitus and Impaired Glucose Regulation). OGTT is more sensitive for diagnosing diabetes and impaired glucose tolerance but is less convenient and reproducible than FPG. It is therefore rarely used routinely, except for diagnosing gestational diabetes and for research purposes.

In practice, diabetes mellitus or impaired fasting glucose regulation is often diagnosed using random measures of plasma glucose or of HbA1C. A random glucose value > 200 mg/dL (> 11.1 mmol/L) may be diagnostic, but values can be affected by recent meals and must be confirmed by repeat testing; testing twice may not be necessary in the presence of symptoms of diabetes.

HbA1C measurements reflect glucose levels over the preceding 3 months. HbA1C measurements are now included in the diagnostic criteria for diabetes:

  • HbA1C 6.5% = diabetes

  • HbA1C 5.7 to 6.4% = prediabetes or at risk of diabetes

However, HbA1C values may be falsely high or low (see Diabetes Mellitus (DM) : Monitoring), and tests must be done in a certified clinical laboratory with an assay that is certified and standardized to a reference assay. Point-of-care HbA1C measurements should not be used for diagnostic purposes, although they can be used for monitoring diabetes control.

Urine glucose measurement, once commonly used, is no longer used for diagnosis or monitoring because it is neither sensitive nor specific.

Pearls & Pitfalls

  • Point-of-care HbA1C tests are not accurate enough to be used for initial diagnosis of diabetes.


Diagnostic Criteria for Diabetes Mellitus and Impaired Glucose Regulation*



Impaired Glucose Regulation


FPG (mg/dL [mmol/L])

<100 (< 5.6)

100–125 (5.6–6.9)

126 (7.0)

OGTT (mg/dL [mmol/L])

< 140 (<7.8)

140–199 (7.8–11.0)

200 ( 11.1)

HbA1C (%)

< 5.7


≥ 6.5

* See also American Diabetes Association: Standards of Medical Care in Diabetes. Diabetes Care 43 (Supplement 1): S1–S212, 2020.

FPG = fasting plasma glucose; HbA1C = glycosylated hemoglobin; OGTT = oral glucose tolerance test, 2-hour glucose level.

Screening for disease

Screening for diabetes mellitus should be conducted for people at risk of the disease. Patients with DM are screened for complications.

People at high risk of type 1 diabetes (eg, siblings and children of people with type 1 diabetes) can be tested for the presence of islet cell or anti-glutamic acid decarboxylase antibodies, which precede onset of clinical disease. However, there are no proven preventive strategies for people at high risk, so such screening is usually reserved for research settings.

Risk factors for type 2 diabetes include

  • Age ≥ 45

  • Overweight or obesity

  • Sedentary lifestyle

  • Family history of diabetes mellitus

  • History of impaired glucose regulation

  • Gestational diabetes mellitus or delivery of a baby > 4.1 kg

  • History of hypertension

  • Dyslipidemia (high-density lipoprotein [HDL] cholesterol < 35 mg/dL [0.9 mmol/L] or triglyceride level > 250 mg/dL [2.8 mmol/L])

  • History of cardiovascular disease

  • Black, Hispanic, Asian American, or American Indian ethnicity

People ≥ age 45 and all adults with additional risk factors described above should be screened for diabetes with an FPG level, HbA1C, or a 2-hour value on a 75-g OGTT at least once every 3 years as long as plasma glucose measurements are normal and at least annually if results reveal impaired fasting glucose levels (see table Diagnostic Criteria for Diabetes Mellitus and Impaired Glucose Regulation).

Screening for complications of diabetes

All patients with type 1 diabetes mellitus should begin screening for diabetic complications 5 years after diagnosis. For patients with type 2 diabetes, screening begins at diagnosis. Typical screening for complications includes

  • Foot examination

  • Funduscopic examination

  • Urine testing for albuminuria

  • Measurement of serum creatinine and lipid profile

Foot examination should be done at least annually for impaired sense of pressure, vibration, pain, or temperature, which is characteristic of peripheral neuropathy. Pressure sense is best tested with a monofilament esthesiometer (see figure Diabetic foot screening). The entire foot, and especially skin beneath the metatarsal heads, should be examined for skin cracking and signs of ischemia, such as ulcerations, gangrene, fungal nail infections, deceased pulses, and hair loss.

Funduscopic examination should be done by an ophthalmologist; the screening interval is typically annually for patients with any retinopathy to every 2 years for those without retinopathy on a prior examination. If retinopathy shows progression, more frequent evaluation may be needed.

Spot or 24-hour urine testing is indicated annually to detect albuminuria, and serum creatinine should be measured annually to assess renal function.

Many physicians consider baseline ECG important given the risk of heart disease. Lipid profile should be checked at least annually and more often when abnormalities are present. Blood pressure should be measured at every examination.

Calculators for Managing Patients With Diabetes

Diagnosis reference

Treatment of Diabetes Mellitus

  • Diet and exercise

  • For type 1 diabetes, insulin

  • For type 2 diabetes, oral antihyperglycemics, injectable glucagon-like peptide-1 (GLP-1) receptor agonists, insulin, or a combination

  • To prevent complications, often renin-angiotensin-aldosterone system blockers (angiotensin-converting enzyme inhibitors or angiotensin II receptor blockers), and statins

Treatment of diabetes mellitus involves both lifestyle changes and drugs. Patients with type 1 diabetes require insulin. Some patients with type 2 diabetes may be able to avoid or cease drug treatment if they are able to maintain plasma glucose levels with diet and exercise alone. For detailed discussion, see Drug Treatment of Diabetes.

Goals and methods

Treatment involves control of hyperglycemia to relieve symptoms and prevent complications while minimizing hypoglycemic episodes.

Goals for glycemic control are

  • Preprandial blood glucose between 80 and 130 mg/dL (4.4 and 7.2 mmol/L)

  • Peak postprandial (1 to 2 hours after beginning of the meal) blood glucose < 180 mg/dL (< 10 mmol/L)

  • HbA1C levels <7%

Glucose levels are typically determined by home monitoring of capillary blood glucose (eg, from a fingerstick) or continuous glucose monitoring and maintenance of HbA1C levels < 7%. These goals may be adjusted for patients in whom strict glucose control may be inadvisable, such as frail older patients; patients with a short life expectancy; patients who experience repeated bouts of hypoglycemia, especially with hypoglycemic unawareness; and patients who cannot communicate the presence of hypoglycemia symptoms (eg, young children, patients with dementia). Conversely, providers may recommend stricter HbA1C goals (< 6.5%) in select patients if these goals can be achieved without hypoglycemia. Potential candidates for tighter glycemic control include patients not being treated with drugs that induce hypoglycemia, those who have short duration of diabetes mellitus, those who have a long life expectancy, and those who have no cardiovascular disease.

Key elements for all patients are patient education, dietary and exercise counseling, and monitoring of glucose control.

All patients with type 1 diabetes require insulin therapy. The goal is to try to replicate the pattern of insulin secretion of a person who does not have diabetes by using basal-bolus insulin therapy, in which a longer-acting insulin is used to simulate basal insulin production that suppresses hepatic glucose production, especially in the fasting state, and a shorter-acting insulin is used before meals to control postprandial glucose excursions. Sliding-scale insulin is a strategy in which varying doses of rapid acting insulin are given before meals and at bedtime depending on the patient's plasma glucose level. However, a sliding scale insulin regimen on its own is not an effective strategy for maintaining euglycemia in patients with type 1 diabetes or in most patients with type 2 diabetes.

Patients with type 2 diabetes and mildly elevated plasma glucose should be prescribed a trial of diet and exercise, followed by an oral antihyperglycemic drug if lifestyle changes are insufficient, additional oral drugs and/or a GLP-1 receptor agonist as needed (combination therapy), and insulin when combination therapy is ineffective for meeting recommended goals. Metformin is usually the first oral drug used. In patients without atherosclerotic cardiovascular disease, heart failure, or chronic kidney disease, there is no evidence to support the use of a particular drug or class of drugs; the decision often involves consideration of adverse effects, convenience, and patient preference. In patients with atherosclerotic cardiovascular disease, a sodium/glucose cotransporter 2 (SGLT2) inhibitor or a GLP-1 receptor agonist may be recommended because of recent evidence that these classes of drugs decrease mortality in these patients. In patients with chronic kidney disease or heart failure, SGLT2-inhibitors should be strongly considered as they may decrease disease progression and mortality

Patients with type 2 diabetes and more significant glucose elevations at diagnosis are typically prescribed lifestyle changes and one or more antihyperglycemic drugs simultaneously.

Insulin is indicated as initial therapy for women with type 2 diabetes who are pregnant and for patients who present with acute metabolic decompensation, such as hyperosmolar hyperglycemic state or diabetic ketoacidosis (DKA). Patients with severe hyperglycemia (plasma glucose > 400 mg/dL [> 22.2 mmol/L]) may respond better to therapy after glucose levels are normalized with a brief period of insulin treatment.

Patients with impaired glucose regulation should receive counseling addressing their risk of developing diabetes and the importance of lifestyle changes for preventing diabetes. They should be monitored closely for development of diabetes symptoms or elevated plasma glucose. Ideal follow-up intervals have not been determined, but annual or biannual checks are probably appropriate.

Patient education

Education is crucial to optimizing care. Education should include information about the following:

  • Causes of diabetes

  • Diet

  • Exercise

  • Drugs

  • Self-monitoring with fingerstick testing

  • Symptoms and signs of hypoglycemia, hyperglycemia, and diabetic complications

Most patients with type 1 diabetes can also be taught how to adjust their insulin doses. Education should be reinforced at every physician visit and hospitalization. Formal diabetes education programs, generally conducted by diabetes nurses and nutrition specialists, are often very effective.


Adjusting diet to individual circumstances can help patients control fluctuations in their glucose level and, for patients with type 2 diabetes mellitus, lose weight. Dietary recommendations should be individualized based on patient tastes, preferences, culture, and goals (1). There are no recommendations on the percentages of calories that should come from carbohydrate, protein, or fat.  Patients should be educated on consuming a diet rich in whole foods rather than processed foods. Carbohydrates should be high quality and should contain adequate amounts of fiber, vitamins, and minerals and low in added sugar, fat, and sodium. Some adults can reduce blood glucose levels and decrease antihyperglycemic drugs by following a low- or very-low–carbohydrate eating plan, although the benefits may not be sustained long-term. 

Patients with type 1 diabetes should use carbohydrate counting or the carbohydrate exchange system to match insulin dose to carbohydrate intake and facilitate physiologic insulin replacement. “Counting” the amount of carbohydrate in the meal is used to calculate the preprandial insulin dose. For example, if a carbohydrate-to-insulin ratio (CIR) of 15 gram:1 unit is used, a patient will require 1 unit of rapid-acting insulin for each 15 g of carbohydrate in a meal. These ratios can vary significantly between patients, depending on their degree of insulin sensitivity and must be tailored to the patient and fine-tuned and adjusted over time. This approach requires detailed patient education and is most successful when guided by a dietitian experienced in working with patients with diabetes. Some experts have advised use of the glycemic index (a measure of the impact of an ingested carbohydrate-containing food on the blood glucose level) to delineate between rapid and slowly metabolized carbohydrates, although there is little evidence to support this approach.

For both type 1 diabetes and type 2 diabetes, nutrition consultation should complement physician counseling; the patient and the person who prepares the patient’s meals should both be present.


Physical activity should increase incrementally to whatever level a patient can tolerate. Both aerobic exercise and resistance exercise have been shown to improve glycemic control in type 2 diabetes, and several studies have shown a combination of resistance and aerobic exercise to be superior to either alone. Also, in type 1 diabetes, exercise has been shown to decrease mortality and improve hemoglobin A1c. Adults with diabetes and without physical limitations should exercise for a minimum of 150 minutes/week (divided over at least 3 days). Exercise has a variable effect on blood glucose, depending on the timing of exercise in relation to meals, and the duration, intensity and type of exercise. In patients with type 1 diabetes in particular, exercise can lead to hypoglycemia. Therefore blood sugar should be monitored immediately before and after exercise. The target range for blood glucose prior to exercise should be between 90 mg/dl and 250mg/dL (5 mmol/L to 14 mmol/L).

Patients who experience hypoglycemic symptoms during exercise should be advised to test their blood glucose and ingest carbohydrates or lower their insulin dose as needed to get their glucose slightly above normal just before exercise. Hypoglycemia during vigorous exercise may require carbohydrate ingestion during the workout period, typically 5 to 15 g of sucrose or another simple sugar.

Patients with known or suspected cardiovascular disease may benefit from exercise stress testing before beginning an exercise program. Activity goals may need to be modified for patients with complications of diabetes such as neuropathy and retinopathy.

Weight loss

In people with diabetes and obesity, physicians should prescribe diabetes drugs that promote weight loss, or are weight neutral, if possible (for details, see Drug Treatment of Diabetes). Other weight loss drugs, including orlistat, phentermine/topiramate, and naltrexone/bupropion, may be useful in selected patients as part of a comprehensive weight loss program. Orlistat, an intestinal lipase inhibitor, reduces dietary fat absorption; it reduces serum lipids and helps promote weight loss. Phentermine/topiramate is a combination drug that reduces appetite through multiple mechanisms in the brain. Many of these drugs also have been shown to significantly decrease HbA1C.

Surgical treatment for obesity, such as sleeve gastrectomy or gastric bypass, also leads to weight loss and improved glucose control (independent of weight loss) in patients who have diabetes mellitus and are unable to lose weight through other means.

Foot care

Regular professional podiatric care, including trimming of toenails and calluses, is important for patients with sensory loss or circulatory impairment. Such patients should be advised to inspect their feet daily for cracks, fissures, calluses, corns, and ulcers. Feet should be washed daily in lukewarm water, using mild soap, and dried gently and thoroughly. A lubricant (eg, lanolin) should be applied to dry, scaly skin. Nonmedicated foot powders should be applied to moist feet. Toenails should be cut, preferably by a podiatrist, straight across and not too close to the skin. Adhesive plasters and tape, harsh chemicals, corn cures, water bottles, and electric pads should not be used on skin. Patients should change stockings daily and not wear constricting clothing (eg, garters, socks or stockings with tight elastic tops).

Shoes should fit well, be wide-toed without open heels or toes, and be changed frequently. Special shoes should be prescribed to reduce trauma if the foot is deformed (eg, previous toe amputation, hammer toe, bunion). Walking barefoot should be avoided.

Patients with neuropathic foot ulcers should avoid weight bearing until ulcers heal. If they cannot, they should wear appropriate orthotic protection. Because most patients with these ulcers have little or no macrovascular occlusive disease, debridement and antibiotics frequently result in good healing and may prevent major surgery. After the ulcer has healed, appropriate inserts or special shoes should be prescribed. In refractory cases, especially if osteomyelitis is present, surgical removal of the metatarsal head (the source of pressure) or amputation of the involved toe or transmetatarsal amputation may be required. A neuropathic joint can often be satisfactorily managed with orthopedic devices (eg, short leg braces, molded shoes, sponge-rubber arch supports, crutches, prostheses).


All patients with diabetes mellitus should be vaccinated against Streptococcus pneumoniae, and influenza virus, and hepatitis B as per standard recommendations.


Diabetes mellitus control can be monitored by measuring blood levels of

  • Glucose

  • HbA1C

  • Fructosamine

Self-monitoring of blood glucose with a glucose meter (using fingertip blood and test strips) or a continuous glucose monitor (CGM) is most important. Technologic improvements in both of these monitoring modalities help patients adjust dietary intake and insulin dosing and help physicians recommend adjustments in the timing and doses of drugs (1).

Many different glucose meters are available. Nearly all require test strips and a means for pricking the skin and obtaining a blood sample. Choice among devices is usually based on patient preferences for features such as time to results (usually 5 to 30 seconds), size of display panel (large screens may benefit patients with poor eyesight), voice readout (for those with visual impairment), and smart phone app connectivity (2).

Continuous glucose monitoring systems using sensors on or under the skin can provide real-time results, including an alarm to warn of hypoglycemia, hyperglycemia, or rapidly changing glucose levels. These systems can be integrated with subcutaneous insulin delivery devices to provide real-time adjustment of blood glucose levels. Such devices are expensive; however, they are becoming more commonly used, and more recent versions do not require daily fingerstick glucose testing to calibrate the glucose monitor. They are especially useful in patients with type 1 diabetes and for those with hypoglycemia unawareness or nocturnal hypoglycemia. Newer continuous glucose monitor sensors can be used for up to 2 weeks before they need to be replaced. Practitioners can review the recorded data to determine whether the patient is experiencing undetected hyper- or hypoglycemia.

Patients with poor glucose control and those given a new drug or a new dose of a currently used drug may be asked to self-monitor 1 (usually morning fasting) to 5 times a day, depending on the patient’s needs and abilities and the complexity of the treatment regimen. Most patients with type 1 diabetes benefit from testing at least 4 times a day.

HbA1C levels reflect glucose control over the preceding 3 months and hence assess control between physician visits. HbA1C should be assessed quarterly in patients with type 1 diabetes and at least twice a year in patients with type 2 diabetes when plasma glucose appears stable and more frequently when control is uncertain. Home testing kits are useful for patients who are able to follow the testing instructions rigorously.

Control suggested by HbA1C values sometimes appears to differ from that suggested by daily glucose readings because of falsely elevated or normal HbA1C values. False elevations of HbA1C may occur with low red blood cell turnover (as occurs with iron, folate, or vitamin B12 deficiency anemia), high-dose aspirin, and high blood alcohol concentrations. Falsely normal HbA1C values occur with increased red blood cell turnover, as occurs with hemolytic anemias and hemoglobinopathies (eg, HbS, HbC) or during treatment of deficiency anemias. In patients with cirrhosis or chronic kidney disease stages 4 and 5, correlation between HbA1C and glycemic levels is poor and HbA1C can be falsely decreased in these patients.

Fructosamine, which is mostly glycosylated albumin but also comprises other glycosylated proteins, reflects glucose control in the previous 1 to 2 weeks. Fructosamine monitoring may be used during intensive treatment of diabetes and for patients with hemoglobin variants or high red blood cell turnover (which cause false HbA1C results), but it is mainly used in research settings.

Urine glucose monitoring is too inaccurate to be recommended. Self-measurement of urine ketones is recommended for patients with type 1 diabetes if they experience symptoms, signs, or triggers of ketoacidosis, such as nausea or vomiting, abdominal pain, fever, cold or flu-like symptoms, or unusual sustained hyperglycemia (> 250 to 300 mg/dL [> 13.9 to 16.7 mmol/L]) during glucose self-monitoring.

Pancreas transplantation

Pancreas transplantation and transplantation of pancreatic islet cells are alternative means of insulin delivery (3); both techniques effectively transplant insulin-producing beta-cells into insulin-deficient (type 1) patients.

Treatment references

Special Populations and Settings

The term brittle diabetes has been used to refer to patients who have dramatic, recurrent swings in glucose levels, often for no apparent reason. However, this concept has no biologic basis and should not be used. Labile plasma glucose levels are more likely to occur in patients with type 1 diabetes because endogenous insulin production is completely absent, and in some patients, counter-regulatory response to hypoglycemia is impaired. Other causes include occult infection, gastroparesis (which leads to erratic absorption of dietary carbohydrates), and endocrine disorders (eg, Addison disease).

Patients with chronic difficulty maintaining acceptable glucose levels should be evaluated for situational factors that affect glucose control. Such factors include inadequate patient education or understanding that leads to errors in insulin administration, inappropriate food choices, and psychosocial stress that expresses itself in erratic patterns of drug use and food intake.

The initial approach is to thoroughly review self-care techniques, including insulin preparation and injection and glucose testing. Increased frequency of self-testing may reveal previously unrecognized patterns and provides the patient with helpful feedback. A thorough dietary history, including timing of meals, should be taken to identify potential contributions to poor control. Underlying disorders should be ruled out by physical examination and appropriate laboratory tests. For some insulin-treated patients, changing to a more intensive regimen that allows for frequent dose adjustments (based on glucose testing) is helpful.


Diabetes in children is discussed in more detail elsewhere.

Children with type 1 diabetes require physiologic insulin replacement as do adults, and similar treatment regimens, including insulin pumps, are used. However, the risk of hypoglycemia, because of unpredictable meal and activity patterns and limited ability to report hypoglycemic symptoms, may require modification of treatment goals. Most young children can be taught to actively participate in their own care, including glucose testing and insulin injections. School personnel and other caregivers must be informed about the disease and instructed about the detection and treatment of hypoglycemic episodes. Screening for microvascular complications can generally be deferred until after puberty.

Children with type 2 diabetes require the same attention to diet and weight control and recognition and management of dyslipidemia and hypertension as do adults. Most children with type 2 diabetes are obese, so lifestyle modification is the cornerstone of therapy. Children with mild hyperglycemia generally begin treatment with metformin unless they have ketosis, renal insufficiency, or another contraindication to metformin use. Dosage is 500 to 1000 mg orally twice a day. If response is insufficient, insulin may be added. Some pediatric specialists also consider using thiazolidinediones, sulfonylureas, GLP-1 receptor agonists, and dipeptidyl peptidase-4 inhibitors as part of combination therapy.


Diabetes in adolescents is discussed in more detail elsewhere. Glucose control typically deteriorates as children with diabetes enter adolescence. Multiple factors contribute, including pubertal and insulin-induced weight gain; hormonal changes that decrease insulin sensitivity; psychosocial factors that lead to insulin nonadherence (eg, mood and anxiety disorders, hectic schedules, irregular meals); family conflict, rebellion, and peer pressure; eating disorders that lead to insulin omission as a means of controlling weight; and experimentation with cigarette, alcohol, and substance use. For these reasons, some adolescents experience recurrent episodes of hyperglycemia and diabetic ketoacidosis requiring emergency department visits and hospitalization.

Treatment often involves intensive medical supervision combined with psychosocial interventions (eg, mentoring or support groups), individual or family therapy, and psychopharmacology when indicated. Patient education is important so that adolescents can safely enjoy the freedoms of early adulthood. Rather than judging personal choices and behaviors, providers must continually reinforce the need for careful glycemic control, especially frequent blood sugar monitoring and use of frequent, low-dose, fast-acting insulins as needed.


Diabetes mellitus can be a primary reason for hospitalization or can accompany other illnesses that require inpatient care. All diabetic patients with diabetic ketoacidosis, hyperosmolar hyperglycemic state, or prolonged or severe hypoglycemia should be hospitalized. Patients with hypoglycemia induced by sulfonylureas, poorly controlled hyperglycemia, or acute worsening of diabetic complications may benefit from brief hospitalization. Children and adolescents with new-onset diabetes may also benefit from hospitalization. Control may worsen on discharge when insulin regimens developed in controlled inpatient settings prove inadequate to the uncontrolled conditions outside the hospital.

When other illnesses mandate hospitalization, some patients can continue on their home diabetes treatment regimens. However, glucose control often proves difficult, and it is often neglected when other diseases are more acute. Restricted physical activity and acute illness worsen hyperglycemia in some patients, whereas dietary restrictions and symptoms that accompany illness (eg, nausea, vomiting, diarrhea, anorexia) precipitate hypoglycemia in others—especially when antihyperglycemic drug doses remain unchanged. In addition, it may be difficult to control glucose adequately in hospitalized patients because usual routines (eg, timing of meals, drugs, and procedures) are inflexibly timed relative to diabetes treatment regimens.

In the inpatient setting, oral antihyperglycemic drugs often need to be stopped. Metformin can cause lactic acidosis in patients with renal insufficiency and has to be stopped if contrast agents need to be given and is, therefore, withheld in all but the most stable hospitalized patients. Sulfonylureas can cause hypoglycemia and should also be stopped. Most patients can be appropriately treated with basal insulin without or with supplemental short-acting insulin. Dipeptidyl peptidase-4 inhibitors are relatively safe, even in patients with kidney disease, and they may also be used for postprandial glucose lowering. Sliding-scale insulin should not be the only intervention to correct hyperglycemia; it is reactive rather than proactive, and data show it leads to poor glycemic control compared to basal-bolus insulin. Longer-acting insulins should be adjusted to prevent hyperglycemia rather than just using short-acting insulins to correct it.

Inpatient hyperglycemia is associated with increased infection rate and mortality. Critical illness causes insulin resistance and hyperglycemia even in patients without known diabetes mellitus. Such stress hyperglycemia is associated with poor outcomes, including increased mortality. Insulin infusion to maintain plasma glucose between 140 and 180 mg/dL (7.8 and 10.0 mmol/L) prevents adverse outcomes such as organ failure, may enhance recovery from stroke, and leads to improved survival in patients requiring prolonged (> 5 days) critical care. Previously, glucose target levels were lower; however, it appears that the less stringent targets as described above may be sufficient to prevent adverse outcomes. Severely ill patients, especially those receiving glucocorticoids or pressors, may need very high doses of insulin (> 5 to 10 units/hour) because of insulin resistance. Insulin infusion should also be considered for patients receiving total parenteral nutrition (TPN). In critically ill patients or post-surgical patients who are in an intensive care unit, insulin infusion protocols and/or computerized algorithms can be used to titrate insulin drips to maintain euglycemia.


The physiologic stress of surgery can increase plasma glucose in patients with diabetes and induce DKA in those with type 1 diabetes. For shorter procedures, subcutaneous insulin can be used. In patients with type 1 diabetes, one half to two thirds of the usual morning dose of intermediate-acting insulin or 70 to 80% of the dose of long-acting insulin (glargine or detemir) can be given the night or morning before surgery (at the usual time of long-acting insulin administration). Patients with type 2 diabetes who are taking insulin should be given 50% of their basal insulin dose on the night or morning before surgery. An IV infusion of a dextrose solution can be started before surgery at a rate of 75-150 mL/hour and titrated to maintain euglycemia. During and after surgery, plasma glucose (and ketones if hyperglycemia suggests the need) should be measured at least every 2 hours. Dextrose infusion can be continued, and regular or short-acting insulin can be given subcutaneously every 4 to 6 hours as needed to maintain the plasma glucose level between 100 and 200 mg/dL (5.5 and 11.1 mmol/L) until the patient can be switched to oral feedings and resume the usual insulin regimen. Additional doses of intermediate- or long-acting insulin should be given if there is a substantial delay (> 24 hours) in resuming the usual regimen. This approach may also be used for insulin-treated patients with type 2 diabetes, but frequent measurement of ketones may be omitted.

Some physicians prefer to withhold subcutaneous or inhaled insulin on the day of surgery and to give insulin by IV infusion. For patients undergoing a long or major surgery, a continuous insulin infusion is preferable, especially since insulin requirements can increase because of the stress of surgery. IV insulin infusion can be given at the same time as intravenous dextrose solution to maintain blood glucose. One approach is to combine glucose, insulin, and potassium in the same bag (GIK regimen), for example, by combining 10% dextrose with 10 mEq (10 mmol) potassium, and 15 units of insulin in a 500-mL bag. The insulin doses are adjusted in 5-unit increments. This approach is not used at many institutions because of the frequent remixing and changing of bags needed to adjust to the patient's level of glycemia. A more common approach in the US is to infuse insulin and dextrose separately. Insulin can be infused at a rate of 1 to 2 U/h with 5% dextrose infusing at 75 to 150 mL/hour. The insulin rate may need to be decreased for patients with more insulin-sensitive type 1 diabetes and increased for patients with more insulin-resistant type 2 diabetes. 10 % dextrose may also be used. It is important, especially in type 1 diabetes, to continue insulin infusion, to avoid development of DKA. Insulin adsorption onto IV tubing can lead to inconsistent effects, which can be minimized by preflushing the IV tubing with insulin solution. Insulin infusion is continued through recovery, with insulin dose adjusted based on the plasma glucose levels obtained in the recovery room and at 1- to 2-hour intervals thereafter.

Most patients with type 2 diabetes who are treated only with oral antihyperglycemic drugs maintain acceptable glucose levels when fasting and may not require insulin in the perioperative period. Most oral drugs, including sulfonylureas and metformin, should be withheld on the day of surgery, and plasma glucose levels should be measured preoperatively and postoperatively and every 6 hours while patients receive IV fluids. Oral drugs may be resumed when patients are able to eat, but metformin should be withheld until normal renal function is confirmed 48 hours after surgery.

Prevention of Diabetes Mellitus

Type 1 diabetes

No treatments definitely prevent the onset or progression of type 1 diabetes mellitus. Azathioprine, corticosteroids, and cyclosporine induce remission of early type 1 diabetes in some patients, presumably through suppression of autoimmune beta-cell destruction. However, toxicity and the need for lifelong treatment limit their use. Anti-CD3 monoclonal antibodies have been shown to reduce insulin requirements for at least the first year of recent-onset disease by suppressing autoimmune T-cell response, and these drugs may delay onset of type 1 diabetes in high-risk family members of patients with type 1 diabetes.

Type 2 diabetes

Type 2 diabetes usually can be prevented with lifestyle modification. Weight loss of as little as 7% of baseline body weight, combined with moderate-intensity physical activity (eg, walking 30 minutes/day), may reduce the incidence of diabetes in high-risk people by > 50%. Metformin and acarbose have also been shown to reduce the risk of diabetes in patients with impaired glucose regulation. Thiazolidinediones may also be protective. However, further study is needed before thiazolidinediones can be recommended for routine preventive use.


Risk of complications of diabetes can be decreased by strict control of plasma glucose, defined as HbA1C < 7%, and by control of hypertension and lipid levels. For patients with diabetes, blood pressure should be maintained at < 140/90 mm Hg, and for those patients who also have heart disease or who are at high risk for heart disease, blood pressure should be maintained at < 130/80 mm Hg. Based on more recent meta-analyses, some professional organizations recommend a goal blood pressure < 130/80 for all patients with diabetes. Specific measures for prevention of progression of complications once detected are described under Complications and Treatment.

Key Points

  • Type 1 diabetes is caused by an absence of insulin due to autoimmune-mediated inflammation in pancreatic beta cells.

  • Type 2 diabetes is caused by hepatic insulin resistance (causing an inability to suppress hepatic glucose production), peripheral insulin resistance (which impairs peripheral glucose uptake) in combination with a beta-cell secretory defect.

  • Microvascular complications include nephropathy, neuropathy, and retinopathy.

  • Macrovascular complications involve atherosclerosis resulting in coronary artery disease, transient ischemic attack/stroke, and peripheral arterial insufficiency.

  • Diagnose by elevated fasting plasma glucose level and/or elevated hemoglobin A1C and/or elevated 2-hour value on oral glucose tolerance test.

  • Do regular screening for complications.

  • Treat with diet, exercise, and insulin, and/or oral or injectable antihyperglycemic drugs.

  • Often, give renin-angiotensin-aldosterone system blockers and statins to prevent complications.

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