Merck Manual

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Erika F. Brutsaert

, MD, New York Medical College

Reviewed/Revised Sep 2022

Hypoglycemia, or low plasma glucose level can result in sympathetic nervous system stimulation, and central nervous system dysfunction. In patients with diabetes who take insulin or antihyperglycemic treatment, hypoglycemia is common and is defined as a glucose level of ≤ 70 mg/dL. In contrast, hypoglycemia unrelated to exogenous insulin therapy is an uncommon clinical syndrome caused by various disorders or drugs. it. Diagnosis requires blood tests done at the time of symptoms or during a 72-hour fast. Treatment of hypoglycemia is provision of glucose combined with treatment of the underlying disorder.

Symptomatic hypoglycemia unrelated to treatment of diabetes mellitus is relatively rare, in part because the body has extensive counter-regulatory mechanisms to compensate for low blood glucose levels. Glucagon and epinephrine levels surge in response to acute hypoglycemia and appear to be the first line of defense. Cortisol and growth hormone levels also increase acutely and are important in the recovery from prolonged hypoglycemia. The threshold for release of these hormones is usually above that for hypoglycemic symptoms. Hereditary or congenital syndromes that cause hypoglycemia in infancy and childhood are not discussed here.

Etiology of Hypoglycemia

Hypoglycemia in patients without diabetes is rare. It can occur in the fasting and/or postprandial state and can be classified as insulin-mediated or non-insulin–mediated.

A helpful practical classification is based on clinical status: whether hypoglycemia occurs in patients who appear healthy or ill.

Insulin-mediated causes include

  • Exogenous insulin

  • Insulin secretagogue (sulfonylurea) use

  • Insulinoma

  • Non-insulinoma pancreatogenous hypoglycemia syndrome (NIPHS)

  • Post-bariatric surgery hypoglycemia

  • Insulin autoimmune hypoglycemia

Insulinoma Insulinoma An insulinoma is a rare pancreatic beta-cell tumor that hypersecretes insulin. The main symptom is fasting hypoglycemia. Diagnosis is by a 48- or 72-hour fast with measurement of glucose and... read more is a rare neuroendocrine tumor of insulin-producing beta cells. It typically causes fasting hypoglycemia although postprandial hypoglycemia can also occur. Post-bariatric surgery hypoglycemia is a hyperinsulinemic hypoglycemia that develops sometimes years after bariatric (especially roux-en-Y gastric bypass) surgery. It is rare, but the true frequency is not known and pathology specimens show nesidioblastosis (hypertrophy of pancreatic beta cells). Hypoglycemia is typically postprandial. NIPHS is a rare condition in which patients have hyperinsulinemic hypoglycemia with negative localizing imaging studies and no history of bariatric surgery. Hypoglycemia is usually postprandial and surgical specimens demonstrate features of nesidioblastosis.

Insulin autoimmune hypoglycemia is a condition that most often occurs in patients with other autoimmune conditions such as systemic lupus erythematosus. Autoantibodies bind to insulin or the receptor and dissociate. Circulating insulin becomes available to bind to the receptor upon dissociation from the antibodies causing hypoglycemia. Treatment is corticosteroids or immunosuppressants.

Non-insulin–mediated causes include

In ill patients, the differential diagnosis also includes insulin-mediated and non-insulin–mediated disorders.

Insulin-mediated disorders include

  • Exogenous insulin

  • Insulin secretagogue (sulfonylurea) use

Non-insulin–mediated disorders include

In ill, hospitalized patients, spontaneous hypoglycemia that is not caused by drugs portends a poor prognosis and can occur when poor nutrition is combined with advanced organ failure (especially liver, kidney, or heart failure) and/or sepsis. Non-islet cell tumor hypoglycemia is a rare condition caused by production of large amounts of aberrant forms of insulin-like growth factor 2 (IGF-2) by a tumor. The aberrant form of IGF-2 binds to the insulin receptor and causes hypoglycemia. By the time hypoglycemia develops, the tumor is usually advanced.

Pseudohypoglycemia occurs when processing of blood specimens in untreated test tubes is delayed and cells, such as red blood cells and leukocytes (especially if increased, as in leukemia or polycythemia), consume glucose. Poor circulation to the digits can also cause erroneously low fingerstick glucose measurements.

Factitious hypoglycemia is true hypoglycemia induced by nontherapeutic administration of sulfonylureas or insulin.

Symptoms and Signs of Hypoglycemia

The surge in autonomic activity in response to low plasma glucose causes sweating, nausea, warmth, anxiety, tremulousness, palpitations, and possibly hunger and paresthesias. Insufficient glucose supply to the brain causes headache, blurred or double vision, confusion, agitation, seizures, and coma. In older patients, hypoglycemia may cause stroke-like symptoms of aphasia or hemiparesis and is more likely to precipitate stroke, myocardial infarction, and sudden death.

Patients with diabetes mellitus of long duration may be unaware of hypoglycemic episodes because they no longer experience autonomic symptoms (hypoglycemia unawareness).

In research studies under controlled conditions, autonomic symptoms begin at or beneath a plasma glucose level of about 60 mg/dL (3.3 mmol/L), whereas central nervous system symptoms occur at or below a glucose level of about 50 mg/dL (2.8 mmol/L). However, symptoms suggestive of hypoglycemia are far more common than the condition itself. In contrast, people with glucose levels at these thresholds may have no symptoms, while people with symptoms suggestive of hypoglycemia can have normal glucose concentrations.

Diagnosis of Hypoglycemia

  • Measurement of blood glucose level

In patients with diabetes who are taking insulin or antihyperglycemic medications, a blood glucose level < 70 mg/dL (3.8 mmol/L) correlated with clinical findings is consistent with hypoglycemia.

The severity of hypoglycemia in patients with diabetes is based on blood glucose levels and need for assistance

  • Level 1 (mild) hypoglycemia: blood glucose < 70 mg/dL (< 3.8 mmol/L) but 54 mg/dL ( 3 mmol/L)

  • Level 2 (moderate) hypoglycemia: blood glucose < 54mg/dL

  • Level 3 (severe) hypoglycemia: hypoglycemia requiring assistance from another person due to change in mental or physical status

In patients not receiving diabetes treatment, diagnosis of a hypoglycemic disorder requires confirmation of Whipple's triad or confirmation of low blood glucose during a fast. Whipple's triad includes

  • Symptoms of hypoglycemia

  • Low plasma glucose level (< 55 mg/dL) that occurs at the time symptoms occur

  • Decrease in symptoms when dextrose or other sugar is given

If a practitioner is present when symptoms occur, blood should be sent for glucose testing in a tube containing a glycolytic inhibitor. If glucose is normal, hypoglycemia is ruled out and other causes of symptoms should be considered. If glucose is abnormally low, and no cause can be identified from history (eg, drugs, adrenal insufficiency, severe malnutrition, organ failure or sepsis), serum insulin, insulin antibodies, and sulfonylurea level should be checked. C-peptide, and proinsulin measured from the same tube can distinguish insulin-mediated from non–insulin-mediated and factitious from physiologic hypoglycemia and can obviate the need for further testing.

In practice, however, it is unusual that practitioners are present when patients experience symptoms suggestive of hypoglycemia. Home glucose meters are unreliable for quantifying hypoglycemia, and there are no clear glycosylated hemoglobin (HbA1C) thresholds that distinguish long-term hypoglycemia from normoglycemia. So the need for more extensive diagnostic testing is based on the probability that an underlying disorder that could cause hypoglycemia exists given a patient’s clinical appearance and coexisting illnesses.

To differentiate between insulin-mediated and non-insulin–mediated hypoglycemia and to determine the etiology of hypoglycemia, a 48- or 72-hour fast may be required.

A 72-hour fast done in a controlled setting is the standard for diagnosis. However, in almost all patients with a hypoglycemic disorder, a 48-hour fast is adequate to detect hypoglycemia and a full 72-hour fast may not be necessary. Patients drink only noncaloric, noncaffeinated beverages, and plasma glucose is measured at baseline, whenever symptoms occur, and every 4 to 6 hours or every 1 to 2 hours if glucose falls below 70 mg/dL (3.8 mmol/L).

Serum insulin, C-peptide, and proinsulin should be measured when a simultaneous plasma glucose is < 55 mg/dL to distinguish endogenous from exogenous (factitious) hypoglycemia. The fast is terminated at 72 hours if the patient has experienced no symptoms and glucose remains normal, sooner if glucose decreases to 45 mg/dL ( 2.5 mmol/L) in the presence of hypoglycemic symptoms.

End-of-fast measurements include beta-hydroxybutyrate (which should be low if the cause is an insulinoma), serum sulfonylurea to detect drug-induced hypoglycemia, and plasma glucose after IV glucagon injection to detect an increase characteristic of insulinoma. Sensitivity, specificity, and predictive values for detecting hypoglycemia by this protocol have not been reported.

There is no definitive lower limit of glucose that unequivocally defines pathologic hypoglycemia during a monitored fast. Normal women tend to have lower fasting glucose levels than men and may have glucose levels as low as 50 mg/dL (2.8 mmol/L) without symptoms. If symptomatic hypoglycemia has not occurred by 48 to 72 hours, the patient should exercise vigorously for about 30 minutes. If hypoglycemia still does not occur, insulinoma is essentially excluded and further testing is generally not indicated.

In patients with postprandial hyperglycemia, fingerstick glucose measurement with laboratory testing after triggering foods can be done.

Treatment of Hypoglycemia

  • Oral sugar or IV dextrose

  • Sometimes parenteral glucagon

Treatment in patients taking antihyperglycemic drugs

Immediate treatment of hypoglycemia involves provision of glucose. Individuals at risk for hypoglycemia should have glucagon or dasiglucagon at home and elsewhere, and household members and trusted others should be instructed on management of hypoglycemic emergencies.

In patients treated with glucose-lowering drugs (insulin or sulfonylureas), a plasma glucose level < 70 mg/dL (< 3.8 mmol/L) is considered hypoglycemia and should be treated to avoid further decreases in blood glucose and consequences of hypoglycemia.

Patients able to eat or drink can drink juices, sucrose water, or glucose solutions; eat candy or other foods; or chew on glucose tablets when symptoms occur.

The rule of 15s should be followed for treatment of hypoglycemia. Typically, 15 g of glucose or sucrose should be ingested. Patients should check their glucose levels 15 minutes after glucose or sucrose ingestion and ingest an additional 15 g if their glucose level is not > 80 mg/dL (> 4.4 mmol/L). After glucose levels improve to > 80 mg/dL, a snack containing a complex carbohydrate and protein may be ingested to prevent the glucose level from dropping again.

Adults and children unable to eat or drink can be given glucagon 0.5 mg (< 25 kg body weight) or 1 mg ( 25 kg) subcutaneously or intramuscularly. Glucagon nasal spray, 3 mg or subcutaneous dasiglucagon, 0.6 mg subcutaneously (available in an autoinjector) may also be used.

For hypoglycemia management in the hospital setting, infants and younger children may be given 10% dextrose solution 2 to 3 mL/kg IV bolus. Adults or older children can be treated with 50% dextrose 50 to 100 mL IV bolus, with or without a continuous infusion of 5 to 10% dextrose solution sufficient to resolve symptoms.

The efficacy of glucagon depends on the size of hepatic glycogen stores; glucagon has little effect on plasma glucose in patients who have been fasting or who are hypoglycemic for long periods.

Hyperglycemia may follow hypoglycemia either because too much sugar was ingested or because hypoglycemia caused a surge in counter-regulatory hormones (glucagon, epinephrine, cortisol, growth hormone).

Treatment in patients not taking antihyperglycemic drugs

Hypoglycemia in patients not taking insulin or a sulfonylurea should also be corrected with oral sugar, IV dextrose or glucagon. Underlying disorders causing hypoglycemia must also be treated. Islet cell and non–islet cell tumors must first be localized, then removed by enucleation or partial pancreatectomy; about 6% recur within 10 years. Diazoxide and octreotide can be used to control symptoms while the patient is awaiting surgery or when a patient refuses or is not a candidate for a procedure.

Non-insulinoma pancreatogenous hypoglycemia syndrome (NIPH) is most often a diagnosis of exclusion after an islet cell tumor is sought but not identified. Diazoxide or octreotide have been used, and partial pancreatectomy may be required for refractory cases.

Patients with hypoglycemia following gastric bypass can sometimes be treated with frequent low carbohydrate meals, but other treatments such as acarbose or diazoxide may be needed.

Drugs that cause hypoglycemia, including alcohol, must be stopped.

Key Points

  • In patients on drug treatment for diabetes, hypoglycemia is a plasma glucose level < 70 mg/dL.

  • Most hypoglycemia is caused by drugs used to treat diabetes mellitus (including surreptitious use); insulin-secreting tumors are rare causes.

  • To diagnose a hypoglycemic disorder not due to diabetes treatment requires a low plasma glucose level (< 55 mg/dL [< 3 mmol/L]) plus simultaneous hypoglycemic symptoms that reverse with dextrose administration.

  • If the etiology of hypoglycemia is unclear, do a 48- or 72-hour fast with measurement of plasma glucose at regular intervals and whenever symptoms occur.

  • Measure serum insulin, C-peptide, and proinsulin at times of hypoglycemia to distinguish endogenous from exogenous (factitious) hypoglycemia.

  • Treat patients with hypoglycemia due to insulin or antihyperglycemic drugs with oral or parenteral glucose and glucagon, depending upon clinical severity.

  • In patients with hypoglycemia not due to insulin or other antihyperglycemic medications, give glucose and glucagon and treat underlying cause.

Drugs Mentioned In This Article

Drug Name Select Trade
Afrezza, Exubera
NebuPent, Pentam
Advocate Glucose SOS, BD Glucose, Dex4 Glucose, Glutol , Glutose 15 , Glutose 45 , Glutose 5
baqsimi, GlucaGen, Glucagon, Gvoke, Gvoke HypoPen, Gvoke PFS
Hyperstat, Proglycem
Bynfezia, Mycapssa, Sandostatin, Sandostatin LAR
NOTE: This is the Professional Version. CONSUMERS: View Consumer Version
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