Merck Manual

Please confirm that you are not located inside the Russian Federation

honeypot link

Diabetes Mellitus (DM)


Erika F. Brutsaert

, MD, New York Medical College

Reviewed/Revised Oct 2023 | Modified Nov 2023
Topic Resources

Diabetes mellitus is a disorder in which the body does not produce enough or respond normally to insulin, causing blood sugar (glucose) levels to be abnormally high.

  • Symptoms of diabetes may include increased urination and thirst, and people may lose weight even if they are not trying to.

  • Diabetes can damage nerves and cause problems with the sense of touch.

  • Diabetes can damage blood vessels and increase the risk of heart attack, stroke, chronic kidney disease, and vision loss.

  • Doctors diagnose diabetes by measuring blood sugar levels.

  • People with diabetes need to follow a healthy diet that is low in refined carbohydrates (including sugar), saturated fat, and processed foods. They also need to exercise, maintain a healthy weight, and usually take medications to lower blood sugar levels and promote weight loss if their weight is above a healthy level.

Diabetes mellitus is a disorder in which the amount of sugar in the blood is elevated. Doctors often use the full name diabetes mellitus, rather than diabetes alone, to distinguish this disorder from arginine vasopressin deficiency ArginineVasopressin Deficiency (Central Diabetes Insipidus) Argininevasopressin deficiency (central diabetes insipidus) is a lack of the hormone vasopressin (antidiuretic hormone) that causes excessive production of very dilute urine (polyuria). Argininevasopressin... read more , which used to be called diabetes insipidus. Argininevasopressin deficiency is a relatively rare disorder that does not affect blood glucose levels but, just like diabetes mellitus, causes increased urination.

Blood sugar

There are many types of sugar. Some sugars are simple, and others are complex. Table sugar (sucrose) is made of two simpler sugars called glucose and fructose. Milk sugar (lactose) is made of glucose and a simple sugar called galactose. The carbohydrates in starches, such as bread, pasta, rice, and similar foods, are long chains of different simple sugar molecules. Sucrose, lactose, carbohydrates, and other complex sugars must be broken down into simple sugars by enzymes in the digestive tract before the body can absorb them.

Once the body absorbs simple sugars, it usually converts them all into glucose, which is an important source of fuel for the body. Glucose is the sugar that is transported through the bloodstream and taken up by cells. The body can also make glucose from fats and proteins. Blood "sugar" really means blood glucose.

Did You Know...

  • There are several types of sugar, "blood sugar" is measured by a blood test for glucose.


Insulin, a hormone released from the pancreas Pancreas The pancreas is an organ that contains two types of glandular tissue: Pancreatic acini Islets of Langerhans (See also Overview of the Digestive System.) The acini produce digestive enzymes.... read more Pancreas (an organ behind the stomach that also produces digestive enzymes), controls the amount of glucose in the blood. Glucose in the bloodstream stimulates the pancreas to produce insulin. Insulin helps glucose to move from the blood into the cells. Once inside the cells, glucose is converted to energy, which is used immediately, or the glucose is stored as fat or the starch glycogen until it is needed.

The levels of glucose in the blood vary normally throughout the day. They rise after a meal and return to pre-meal levels within about 2 hours after eating. Once the levels of glucose in the blood return to pre-meal levels, insulin production decreases. The variation in blood glucose levels is usually within a narrow range, about 70 to 110 milligrams per deciliter (mg/dL), or 3.9 to 6.1 millimoles per liter (mmol/L) of blood in healthy people. If people eat a large amount of carbohydrates, the levels may increase more. People older than 65 years tend to have slightly higher levels, especially after eating.

If the body does not produce enough insulin to move the glucose into the cells, or if the cells stop responding normally to insulin (called insulin resistance), the resulting high levels of glucose in the blood and the inadequate amount of glucose in the cells together produce the symptoms and complications of diabetes Complications of Diabetes Mellitus People with diabetes mellitus have many serious long-term complications that affect many areas of the body, particularly the blood vessels, nerves, eyes, and kidneys. (See also Diabetes Mellitus... read more Complications of Diabetes Mellitus .

Types of Diabetes


Prediabetes is a condition in which blood glucose levels are too high to be considered normal but not high enough to be labeled diabetes. People have prediabetes if their fasting blood glucose level is between 100 mg/dL (5.6 mmol/L) and 125 mg/dL (6.9 mmol/L) or if their blood glucose level 2 hours after a glucose tolerance test is between 140 mg/dL (7.8 mmol/L) and 199 mg/dL (11.0 mmol/L). Prediabetes carries a higher risk of future diabetes as well as heart disease. Decreasing body weight by 5 to 10% through diet and exercise can significantly reduce the risk of developing diabetes.

Type 1 diabetes

In type 1 diabetes (formerly called insulin-dependent diabetes or juvenile-onset diabetes), the body's immune system attacks the insulin-producing cells of the pancreas, and more than 90% of them are permanently destroyed. The pancreas, therefore, produces little or no insulin. Fewer than 10% of all people with diabetes have type 1 disease. Most people who have type 1 diabetes develop the disease before age 30, although it can develop later in life.

Scientists believe that an environmental factor—possibly a viral infection or a nutritional factor during childhood or early adulthood—causes the immune system to destroy the insulin-producing cells of the pancreas. A genetic predisposition makes some people more susceptible to an environmental factor.

When an adult's immune system attacks the cells of the pancreas, diabetes develops more slowly than when a child's immune system attacks. Some adults do not need insulin when diabetes first develops. This form of diabetes, called latent autoimmune diabetes of adulthood (LADA), is rare but may initially be mistaken for type 2 diabetes.

Type 2 diabetes

In type 2 diabetes (formerly called non–insulin-dependent diabetes or adult-onset diabetes), the pancreas often continues to produce insulin, sometimes even at higher-than-normal levels, especially early in the disease. However, the body develops resistance to the effects of insulin, so there is not enough insulin to meet the body’s needs. As type 2 diabetes progresses, the insulin-producing ability of the pancreas decreases.

Type 2 diabetes was once rare in children and adolescents but has become more common. However, it usually begins in people older than 30 years and becomes progressively more common with age. About 30% of people older than 65 have type 2 diabetes.

Obesity Obesity Obesity is a chronic, recurring complex disorder characterized by excess body weight. Obesity is influenced by a combination of factors that includes genetics, hormones, behavior, and the environment... read more Obesity is the chief risk factor for developing type 2 diabetes, and 80 to 90% of people with type 2 diabetes have overweight or obesity. Because obesity causes insulin resistance, people with obesity may need large amounts of insulin to maintain normal blood glucose levels.

People of African, Asian American, American Indian, Alaska Native, and Spanish or Latin American ancestry are at increased risk of developing type 2 diabetes. Type 2 diabetes tends to run in families.

Certain disorders and medications can affect the way the body uses insulin and can lead to type 2 diabetes.

Examples of common states (conditions) that result in impaired insulin use are

Diabetes Mellitus

Symptoms of Diabetes Mellitus

Many patients with diabetes may have no symptoms, especially in the early phase of the disease. However, the two types of diabetes can have very similar symptoms if the blood glucose is significantly elevated.

The symptoms of high blood glucose levels include

  • Increased thirst

  • Increased urination

  • Increased hunger

When the blood glucose level rises above 160 to 180 mg/dL (8.9 to 10.0 mmol/L), glucose spills into the urine. When the level of glucose in the urine rises even higher, the kidneys excrete additional water to dilute the large amount of glucose. Because the kidneys produce excessive urine, people with diabetes urinate large volumes frequently (polyuria Excessive or Frequent Urination Most people urinate about 4 to 6 times a day, mostly in the daytime. Normally, adults pass between 3 cups (700 milliliters) and 3 quarts (3 liters) of urine a day. Excessive urination can refer... read more ). The excessive urination creates abnormal thirst (polydipsia). Because excessive calories are lost in the urine, people may lose weight. To compensate, people often feel excessively hungry.

Other symptoms of diabetes include

  • Blurred vision

  • Drowsiness

  • Nausea

  • Decreased endurance during exercise

Type 1 diabetes

In people with type 1 diabetes, the symptoms often begin abruptly and dramatically. A serious condition called diabetic ketoacidosis Diabetic Ketoacidosis Diabetic ketoacidosis is an acute complication of diabetes that occurs mostly in type 1 diabetes mellitus. Symptoms of diabetic ketoacidosis include nausea, vomiting, abdominal pain, and a characteristic... read more , a complication in which the body produces excess acid, may quickly develop. In addition to the usual diabetes symptoms of excessive thirst and excessive urination, the initial symptoms of diabetic ketoacidosis also include nausea, vomiting, fatigue, and—particularly in children—abdominal pain. Breathing tends to become deep and rapid as the body attempts to correct the blood’s acidity (see Acidosis Acidosis Acidosis is caused by an overproduction of acid that builds up in the blood or an excessive loss of bicarbonate from the blood (metabolic acidosis) or by a buildup of carbon dioxide in the blood... read more ), and the breath smells fruity or like nail polish remover. Without treatment, diabetic ketoacidosis can progress to coma and death, sometimes very quickly.

Type 1 diabetes mellitus progresses in stages:

  • Stage 1: Presence in the blood of two or more diabetes-specific antibodies (substances or markers that indicate that there is inflammation or damage to the insulin-producing cells of the pancreas) in people with normal blood sugar levels and no symptoms of diabetes

  • Stage 2: Higher than normal level of glucose in the blood in people without symptoms

  • Stage 3: Symptoms of diabetes

After type 1 diabetes has begun, some people can have a temporary phase of near-normal glucose levels (honeymoon phase) due to partial recovery of insulin secretion.

Type 2 diabetes

People with type 2 diabetes may not have any symptoms for years or decades before they are diagnosed. Symptoms may be subtle. Increased urination and thirst are mild at first and gradually worsen over weeks or months. Eventually, people feel extremely fatigued, are likely to develop blurred vision, and may become dehydrated.

Because people with type 2 diabetes produce some insulin, ketoacidosis Diabetic Ketoacidosis Diabetic ketoacidosis is an acute complication of diabetes that occurs mostly in type 1 diabetes mellitus. Symptoms of diabetic ketoacidosis include nausea, vomiting, abdominal pain, and a characteristic... read more does not usually develop even when type 2 diabetes is untreated for a long time. Rarely, the blood glucose levels become extremely high (even exceeding 1,000 mg/dL [55.5 mmol/L]). Such high levels often happen as the result of some superimposed stress, such as an infection or medication use. When the blood glucose levels get very high, people may develop severe dehydration Dehydration Dehydration is a deficiency of water in the body. Vomiting, diarrhea, excessive sweating, burns, kidney failure, and use of diuretics may cause dehydration. People feel thirsty, and as dehydration... read more , which may lead to mental confusion, drowsiness, and seizures, a condition called hyperosmolar hyperglycemic state Hyperosmolar Hyperglycemic State (HHS) Hyperosmolar hyperglycemic state is a complication of diabetes mellitus that most often occurs in type 2 diabetes. Symptoms of hyperosmolar hyperglycemic state include extreme dehydration and... read more . Many people with type 2 diabetes are diagnosed by routine blood glucose testing before they develop such severely high blood glucose levels.

Complications of diabetes

Diabetes damages blood vessels, causing them to narrow and therefore restricting blood flow. Because blood vessels throughout the body are affected, people may have many complications of diabetes Complications of Diabetes Mellitus People with diabetes mellitus have many serious long-term complications that affect many areas of the body, particularly the blood vessels, nerves, eyes, and kidneys. (See also Diabetes Mellitus... read more Complications of Diabetes Mellitus . Many organs can be affected, particularly the following:

High blood glucose levels also cause disturbances in the body's immune system, so people with diabetes mellitus are particularly susceptible to bacterial and fungal infections.

Diagnosis of Diabetes Mellitus

  • Measuring the level of glucose in the blood

The diagnosis of diabetes is made when people have abnormally high levels of glucose in the blood. Doctors do screening tests Screening for Diabetes Diabetes mellitus is a disorder in which the body does not produce enough or respond normally to insulin, causing blood sugar (glucose) levels to be abnormally high. Symptoms of diabetes may... read more on people who are at risk of diabetes but have no symptoms.

Did You Know...

  • People may have type 2 diabetes and no symptoms, so it is important for people with risk factors to have recommended screening tests.

Blood glucose measurement

Doctors check blood glucose levels in people who have symptoms of diabetes, such as increased thirst, urination, or hunger. Additionally, doctors may check blood glucose levels in people who have disorders that can be complications of diabetes, such as frequent infections, foot ulcers, and yeast infections.

To accurately evaluate blood glucose levels, doctors usually use a blood sample taken after people have fasted overnight. Diabetes can be diagnosed if fasting blood glucose levels are 126 mg/dL (7.0 mmol/L) or higher. However, it is possible to use blood samples taken after people have eaten. Some elevation of blood glucose levels after eating is normal, but even after a meal the levels should not be very high. Diabetes can be diagnosed if a random (not done after fasting) blood glucose level is higher than 200 mg/dL (11.1 mmol/L).

Hemoglobin A1C

Doctors can also measure the level of a protein, hemoglobin A1C (also called glycosylated or glycolated hemoglobin), in the blood, which reflects the person's long-term trends in blood glucose levels rather than rapid changes.

Hemoglobin is the red, oxygen-carrying substance in red blood cells. When blood is exposed to high blood glucose levels over a period of time, glucose attaches to the hemoglobin and forms glycosylated hemoglobin. The hemoglobin A1C level blood test is reported as the percentage of hemoglobin that is A1C .

Measurements of hemoglobin A1C can be used to diagnose diabetes when testing is done by a certified laboratory (not by instruments used at home or in a doctor's office). People with a hemoglobin A1C level of 6.5% or more have diabetes. If the level is between 5.7 and 6.4, they have prediabetes and are at risk of developing diabetes.

Oral glucose tolerance test

Another kind of blood test, an oral glucose tolerance test, may be done in certain situations, such as screening pregnant women for gestational diabetes Gestational diabetes For women who have diabetes before they become pregnant, the risks of complications during pregnancy depend on how long diabetes has been present and whether complications of diabetes, such... read more or testing older adults who have symptoms of diabetes but normal glucose levels when fasting. However, it is not routinely used for testing for diabetes because the test can be very cumbersome.

In this test, people fast, have a blood sample taken to determine the fasting blood glucose level, and then drink a special solution containing a large, standard amount of glucose. More blood samples are then taken over the next 2 to 3 hours and are tested to determine whether the glucose in the blood rises to abnormally high levels.

Screening for Diabetes

Blood glucose levels are often checked during a routine physical examination. Checking the levels of glucose in the blood regularly is particularly important in older adults because diabetes is so common in later life. People may have diabetes, particularly type 2 diabetes, and not know it.

Screening for type 1 diabetes

Screening for type 1 diabetes is not recommended for all children or adults. Doctors sometimes do tests to screen for type 1 diabetes in people at high risk of type 1 diabetes (such as siblings or children of people who have type 1 diabetes). Testing for insulin antibodies allow doctors to identify people with early stage type 1 diabetes and start preventive measures.

Screening for type 2 diabetes

It is important to do screening tests in people at risk of type 2 diabetes, including those who

People with these risk factors should be screened for diabetes at least once every three years.

Diabetes risk can also be estimated using a risk calculators from the American Diabetes Association. Doctors may measure fasting blood glucose levels and hemoglobin A1C level, or do an oral glucose tolerance test. If the test results are on the border between normal and abnormal, doctors do the screening tests more often, at least once a year.

Treatment of Diabetes Mellitus

  • Diet

  • Exercise

  • Weight loss

  • Education

  • In type 1 diabetes, insulin injections

  • In type 2 diabetes, often medications by mouth and sometimes insulin or other medications by injection

Diet, exercise, and education are the cornerstones of treatment of diabetes. Weight loss is important for people who have overweight. Some people with type 2 diabetes and mildly elevated glucose levels can start with diet, exercise, and weight loss only. However, in people with more severe glucose abnormalities, or in whom lifestyle modification is not sufficient to normalize glucose, diabetes medications are required. People with type 1 diabetes (no matter their blood glucose levels) require medication when first diagnosed.

Because complications are less likely to develop if people with diabetes strictly control their blood glucose levels, the goal of diabetes treatment is to keep blood glucose levels as close to the normal range as possible.

It is helpful for people with diabetes to carry or wear medical identification (such as a bracelet or tag) to alert health care professionals to the presence of diabetes. This information allows health care professionals to start life-saving treatment quickly, especially in the case of injury or change in mental status.

General treatment of diabetes

Diet for people with diabetes

Diet management is very important for people with either type of diabetes mellitus. Doctors recommend a healthy, balanced diet and efforts to maintain a healthy weight. People with diabetes can benefit from meeting with a dietitian or a diabetes educator to develop an optimal eating plan. Such a plan includes

  • Avoiding simple sugars and processed foods

  • Increasing dietary fiber

  • Limiting portions of carbohydrate-rich and fatty foods (especially saturated fats)

People who are taking insulin should avoid long periods between meals to prevent hypoglycemia Hypoglycemia Hypoglycemia is abnormally low levels of sugar (glucose) in the blood. Hypoglycemia is most often caused by medications taken to control diabetes. Much less common causes of hypoglycemia include... read more . Although protein and fat in the diet contribute to the number of calories a person eats, only the number of carbohydrates has a direct effect on blood glucose levels. The American Diabetes Association has many helpful tips on diet, including recipes. Even when people follow a proper diet, cholesterol-lowering medication Lipid-lowering drugs Dyslipidemia is a high level of cholesterol and/or triglycerides or a low level of high-density lipoprotein (HDL) cholesterol. Lifestyle, genetics, disorders (such as low thyroid hormone levels... read more Lipid-lowering drugs is needed to decrease the risk of heart disease.

People with type 1 diabetes and certain people with type 2 diabetes may use carbohydrate counting or the carbohydrate exchange system to match their insulin dose to the carbohydrate content of their meal. "Counting" the amount of carbohydrate in a meal is used to calculate the amount of insulin the person takes before eating. However, the carbohydrate-to-insulin ratio (the amount of insulin taken for each gram of carbohydrate in the meal) varies for each person, and people with diabetes need to work closely with a dietician who has experience in working with people with diabetes to master the technique. 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.

Exercise for people with diabetes

Exercise, in appropriate amounts (at least 150 minutes a week spread out over at least 3 days), can also help people control their weight and improve blood glucose levels. Because blood glucose levels go down during exercise, people must be alert for symptoms of hypoglycemia Symptoms Hypoglycemia is abnormally low levels of sugar (glucose) in the blood. Hypoglycemia is most often caused by medications taken to control diabetes. Much less common causes of hypoglycemia include... read more . Some people need to eat a small snack during prolonged exercise, decrease their insulin dose, or both.

Weight loss for people with diabetes

Many people, especially those with type 2 diabetes, have overweight or obesity. Some people with type 2 diabetes may be able to avoid or delay the need to take medications by achieving and maintaining a healthy weight. Weight loss is also important in these people because excess weight contributes to complications of diabetes. When people with obesity and diabetes have trouble losing weight with diet and exercise alone, doctors may give a weight-loss medication or recommend bariatric surgery Metabolic and Bariatric Surgery Metabolic and bariatric (weight-loss) surgery alters the stomach, intestine, or both to produce weight loss in people have obesity or overweight and have metabolic disorders related to obesity... read more (surgery to cause weight loss). Certain diabetes medications can induce weight loss Medications Obesity is a chronic, recurring complex disorder characterized by excess body weight. Obesity is influenced by a combination of factors that includes genetics, hormones, behavior, and the environment... read more Medications , especially glucagon-like peptide 1 (GLP-1) and sodium-glucose co-transporter-2 (SGLT2) inhibitor medications.

Treatment to prevent complications of diabetes

Because diabetes eventually affects blood vessels throughout the body, people with diabetes are likely to develop complications Complications of Diabetes Mellitus People with diabetes mellitus have many serious long-term complications that affect many areas of the body, particularly the blood vessels, nerves, eyes, and kidneys. (See also Diabetes Mellitus... read more Complications of Diabetes Mellitus related to problems with blood vessels. Glucose that remains high for long periods causes build-up in the walls of blood vessels, causing them to thicken and leak and risking development of atherosclerosis, stroke, eye problems, and other problems.

Because the risk of complications is so high in people with diabetes, it is important that people carefully control blood glucose levels. Doctors also recommend that people undergo regular monitoring Monitoring and Preventing Diabetes Complications People with diabetes mellitus have many serious long-term complications that affect many areas of the body, particularly the blood vessels, nerves, eyes, and kidneys. (See also Diabetes Mellitus... read more Monitoring and Preventing Diabetes Complications to prevent complications.

Medication treatment of diabetes

There are many medications used to treat diabetes Medication Treatment of Diabetes Mellitus Many people with diabetes require medication to lower blood glucose levels, relieve symptoms, and prevent complications of diabetes. There are two types of diabetes mellitus Type 1, in which... read more Medication Treatment of Diabetes Mellitus . People with type 1 diabetes require insulin injections to lower blood glucose levels. Most people with type 2 diabetes require medications by mouth to lower blood glucose levels but some also require insulin or other injectable medications.

Pancreas transplantation

People with type 1 diabetes sometimes receive transplantation of an entire pancreas or of only the insulin-producing cells from a donor pancreas. This procedure may allow people with type 1 diabetes mellitus to maintain normal glucose levels. However, because immunosuppressant medications must be given to prevent the body from rejecting the transplanted cells, pancreas transplantation Pancreas Transplantation Pancreas transplantation is the removal of a healthy pancreas from a recently deceased person or rarely a part of a pancreas from a living person and its transfer into person with severe diabetes... read more is usually done only in people who have serious complications due to diabetes or who are receiving another transplanted organ (such as a kidney) and will require immunosuppressants anyway.

People who are frail or have medical problems

Older adults and people with many medical problems, particularly serious problems, need to follow the same general principles of diabetes management—education, diet, exercise, and medications—as younger or healthier people. However, risking hypoglycemia Hypoglycemia Hypoglycemia is abnormally low levels of sugar (glucose) in the blood. Hypoglycemia is most often caused by medications taken to control diabetes. Much less common causes of hypoglycemia include... read more (a low blood glucose level) by trying to strictly control blood glucose levels may be harmful for frail people or people with many medical problems.

Poor eyesight may make it hard for people to read glucose meters and dose scales on insulin syringes. People with arthritis or Parkinson disease or who have had a stroke may have problems manipulating the syringe.


In addition to learning about diabetes itself, people with many medical problems may have to learn how to fit management of diabetes in with their management of other conditions. Learning about how to avoid complications, such as dehydration, skin breakdown, and circulation problems, and to manage factors that can contribute to complications of diabetes, such as high blood pressure and high cholesterol levels, is especially important. Such problems become more common as people age, whether they have diabetes or not.


Many older adults have difficulty following a healthy, balanced diet that can control blood glucose levels and weight. Changing long-held food preferences and dietary habits may be hard. Some people have other disorders that can be affected by diet and may not understand how to integrate the dietary recommendations for their various disorders.

Some people cannot control what they eat because someone else is cooking for them—at home or in a nursing home or other institution. When people with diabetes do not do their own cooking, the people who shop and prepare meals for them must also understand the diet that is needed. These people and their caregivers usually benefit from meeting with a dietitian to develop a healthy, feasible eating plan.


Some people may have a difficult time adding exercise to their daily life, particularly if they have not been active in the past or if they have a disorder that limits their movement, such as arthritis. However, they may be able to add exercise to their usual routine. For example, people can walk instead of drive or climb the stairs instead of taking the elevator.


Taking the medications used to treat diabetes, particularly insulin, may be difficult for some people. For those with vision problems or other problems that make accurately filling a syringe difficult, a caregiver can prepare the syringes ahead of time and store them in the refrigerator. People whose insulin dose is stable may purchase prefilled syringes. Prefilled insulin pen devices may be easier for people with physical limitations. Some of these devices have large numbers and easy-to-turn dials.

Monitoring blood glucose levels

Poor vision, limited manual dexterity due to arthritis, tremor, or stroke, or other physical limitations may make monitoring blood glucose levels more difficult for some people. However, special monitors are available. Some have large numerical displays that are easier to read. Some provide audible instructions and results. Some monitors read blood glucose levels through the skin and do not require a blood sample. People can consult a diabetes educator to determine which meter is most appropriate.


The most common complication of treating high blood glucose levels is low blood glucose levels (hypoglycemia Hypoglycemia Hypoglycemia is abnormally low levels of sugar (glucose) in the blood. Hypoglycemia is most often caused by medications taken to control diabetes. Much less common causes of hypoglycemia include... read more ). The risk is greatest for people who are frail, who are sick enough to require frequent hospital admissions, or who are taking several medications. Of all available medications to treat diabetes, long-acting sulfonylurea medications or insulin are most likely to cause low blood glucose levels in people with severe or many medical problems and especially in older adults. When they take these medications, these people are also more likely to have serious symptoms, such as fainting and falling, and to have difficulty thinking or using parts of the body due to low blood glucose levels.

In older adults, hypoglycemia may be less obvious than in younger people. Confusion caused by hypoglycemia may be mistaken for dementia Dementia Dementia is a slow, progressive decline in mental function including memory, thinking, judgment, and the ability to learn. Typically, symptoms include memory loss, problems using language and... read more or the sedative effect of medications. Also, people who have difficulty communicating (as after a stroke Overview of Stroke A stroke occurs when an artery to the brain becomes blocked or ruptures, resulting in death of an area of brain tissue due to loss of its blood supply (cerebral infarction). Symptoms occur suddenly... read more or as a result of dementia) may not be able to let anyone know they are having symptoms.

People with difficulty maintaining blood glucose levels

People with type 1 diabetes may have more frequent swings in blood glucose levels because insulin production is completely absent. Infection, delayed movement of food through the stomach, and other hormonal disorders may also contribute to blood glucose swings.

In all people who have difficulty controlling blood glucose, doctors look for other disorders that might be causing the problem and also give people additional education on how to monitor diabetes and take their medications.

Monitoring Diabetes Treatment

Monitoring blood glucose levels is an essential part of diabetes care. Routine blood glucose monitoring provides the information needed to make necessary adjustments in medications, diet, and exercise regimens. It is potentially harmful to wait until there are symptoms of low or high blood glucose levels to check blood glucose.

Diabetes treatment goals

Experts recommend that people keep their blood glucose levels

  • Between 80 and 130 mg/dL (4.4 and 7.2 mmol/L) fasting (before meals)

  • Less than 180 mg/dL (10.0 mmol/L) 2 hours after meals

Hemoglobin A1C levels should be less than 7%.

Some people use a continuous glucose monitor (CGM), an external device that is attached to the body and continuously records blood glucose levels. When this type of device is used, doctors use a different measurement to determine how well blood glucose levels are being controlled. They use a value called time in range. Time in range is the percentage of time over a specific period that the blood glucose level is at the person's goal level. The usual range is 70 to 180 mg/mL (3.9 to 9.9 mmol/L).

Because aggressive treatment to reach these goals increases the risk that blood glucose might go too low (hypoglycemia Hypoglycemia Hypoglycemia is abnormally low levels of sugar (glucose) in the blood. Hypoglycemia is most often caused by medications taken to control diabetes. Much less common causes of hypoglycemia include... read more ), these goals are adjusted for some people in whom hypoglycemia is particularly undesirable, such as older adults.

Some other goals are keeping systolic blood pressure less than 140 mm Hg and diastolic blood pressure less than 90 mm Hg. For people with diabetes who have heart disease or are at high risk for heart disease, the blood pressure goal is less than 130/80 mm Hg.

Many things cause blood glucose levels to change:

  • Diet

  • Exercise

  • Stress

  • Illness

  • Medications

  • Time of day

The blood glucose levels may jump after people eat foods high in carbohydrates. Emotional stress, an infection, and many medications tend to increase blood glucose levels. Blood glucose levels increase in many people in the early morning hours because of the normal release of hormones (growth hormone and cortisol), a reaction called the dawn phenomenon. Blood glucose may shoot too high if the body releases certain hormones in response to low blood glucose levels (Somogyi effect). Exercise may cause the levels of glucose in the blood to fall low.

Monitoring blood glucose levels

Blood glucose levels can be measured easily at home or anywhere.

A fingerstick glucose test is most often used to monitor blood glucose. Most blood glucose monitoring devices (glucose meters) use a drop of blood obtained by pricking the tip of the finger with a small lancet. The lancet holds a tiny needle that can be poked into the finger or placed in a spring-loaded device that easily and quickly pierces the skin. Most people find that the pricking causes only minimal discomfort. Then, a drop of blood is placed on a reagent strip. The strip contains chemicals that undergo changes depending on the glucose level. The glucose meter reads the changes in the test strip and reports the result on a digital display. Some devices allow the blood sample to be obtained from other sites, such as the palm, forearm, upper arm, thigh, or calf. Home glucose meters are smaller than a deck of cards.

Continuous glucose monitoring (CGM) systems use a small glucose sensor placed under the skin. The sensor measures blood glucose levels every few minutes. There are two types of CGMs, with different purposes:

  • Professional

  • Personal

Professional CGMs collect continuous blood glucose information over a period of time (72 hours to up to 14 days). Clinicians use this information to make treatment recommendations. Professional CGMs do not provide data to the person with diabetes.

Personal CGMs are used by the person and provide real-time blood glucose data on a small portable monitor or on a connected smart phone. Alarms on the CGM system can be set to sound when blood glucose levels drop too low or climb too high, so the device can help people quickly identify worrisome changes in blood glucose.

CGMs can be worn for up to 14 days, often do not require calibration, and can be used for insulin dosing without fingerstick glucose confirmation. There are also systems in which the CGM device communicates with insulin pumps Insulin Replacement Therapy Many people with diabetes require medication to lower blood glucose levels, relieve symptoms, and prevent complications of diabetes. There are two types of diabetes mellitus Type 1, in which... read more Insulin Replacement Therapy to either stop delivery of insulin when blood glucose is dropping (threshold suspend), or to give daily insulin (hybrid closed loop system).

CGM systems are particularly helpful in certain circumstances, such as in people with type 1 diabetes who have frequent, rapid changes in blood glucose (particularly when the glucose levels sometimes go very low), which are difficult to identify with fingerstick testing. CGM systems allow people to measure the period of time that their blood glucose stays within a certain range, and doctors use this measurement to set goals for treatment and adjust insulin dose. Even in people who don't use insulin, CGM systems can provide valuable information about how different foods and activities affect their blood sugar.

People should keep a record of blood glucose levels and report them to their doctor or nurse, or bring their meter or CGM reader to visits, to help doctors and nurses provide advice in adjusting the dose of insulin or the oral antihyperglycemic medication. Many people can learn to adjust the insulin dose on their own as necessary. Some people who have mild or early type 2 diabetes that is well-controlled with one or two medications may be able to monitor their fingerstick glucose levels relatively infrequently.

Hemoglobin A1C

Doctors can monitor treatment using a blood test called hemoglobin A1C. When the blood glucose levels are high, changes occur in hemoglobin, the protein that carries oxygen in the blood. These changes are in direct proportion to the blood glucose levels over an extended period. The higher the hemoglobin A1C level, the higher the person's glucose levels have been. Thus, unlike the blood glucose measurement, which reveals the level at a particular moment, the hemoglobin A1C measurement demonstrates whether the blood glucose levels have been controlled over the previous few months.

People with diabetes aim for a hemoglobin A1C level of less than 7%. Achieving this level is sometimes difficult, but the lower the hemoglobin A1C level, the less likely people are to have complications. Doctors may recommend a slightly higher or lower target for certain people depending on their particular health situation. However, levels above 9% show poor control, and levels above 12% show very poor control. Most doctors who specialize in diabetes care recommend that hemoglobin A1C be measured every 3 to 6 months.


Urine glucose

Although urine can also be tested for the presence of glucose, checking urine is not a good way to monitor or adjust treatment. Urine testing can be misleading because the amount of glucose in the urine may not reflect the current level of glucose in the blood. Blood glucose levels can get very low or reasonably high without any change in the glucose levels in the urine.

Prevention of Diabetes Mellitus

Type 1 diabetes

No treatments can completely prevent type 1 diabetes mellitus. However, family members of people with type 1 diabetes may have screening tests done and if the tests show they have anti-insulin antibodies, but have not yet had symptoms of diabetes (stage 1), they may benefit from a medication (teplizumab). This medication may prolong the ability of the pancreas to produce insulin and delay the onset of symptoms of type 1 diabetes.

Type 2 diabetes

Type 2 diabetes can be prevented with lifestyle changes. People who have overweight and lose as little as 7 percent of their body weight and who increase physical activity (for example, walking 30 minutes per day) can decrease their risk of diabetes mellitus by more than 50%. Metformin, a medication that is used to treat diabetes, may reduce the risk of diabetes in people with impaired glucose regulation.

More Information

The following English-language resources may be useful. Please note that THE MANUAL is not responsible for the content of the resources.

Drugs Mentioned In This Article

Generic Name Select Brand Names
Arginine, Nutricia SHS L-Arginine, R-Gene
Pitressin, Vasostrict
Deltasone, Predone, RAYOS, Sterapred, Sterapred DS
Afrezza, Exubera
Fortamet, Glucophage, Glucophage XR, Glumetza, Riomet, RIOMET ER
quiz link

Test your knowledge

Take a Quiz!