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Last updated: March 22, 2021

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Hypoglycemia, or low blood glucose, has many causes, but it most commonly occurs in diabetic patients as a consequence of insulin therapy or other drugs. The onset of hypoglycemic symptoms depends largely on the individual's physiological adaptation mechanisms, although symptoms can start to occur when blood glucose falls below 70 mg/dL. Hypoglycemia manifests with autonomic symptoms (i.e., hunger, sweating, tachycardia) and neuroglycopenic symptoms (i.e., confusion, behavioral changes, somnolence). Since prolonged hypoglycemia can result in acute brain damage, changes in a patient's mental status should prompt immediate fingerstick blood glucose measurement and treatment. Treatment in patients who are still conscious consists of a fast-acting carbohydrate such as glucose tablets, candy, or juice. Unresponsive patients are treated with intravenous dextrose or intramuscular glucagon.

  • Defining cutoff: There is no specific cutoff that defines hypoglycemia, as there is considerable variability in the serum glucose level at which a person will experience symptoms of hypoglycemia.
  • In patients with diabetes: generally described as 70 mg/dL (≤ 3.9 mmol/L). [1]
  • Whipple triad [1][2]
    1. Low plasma glucose concentration
    2. Signs or symptoms consistent with hypoglycemia (see “Clinical features” below)
    3. Relief of symptoms when plasma glucose increases after treatment

Diabetic patients [2][3]

Causes of hypoglycemia in diabetic patients
Acute illness

(Relative) overdose of insulin or a noninsulin drug is by far the most common cause of hypoglycemia.

Consider factitious disorder in patients with access to insulin and other diabetes medications (e.g., healthcare professionals), for whom there is no other obvious explanation for hypoglycemia.

Nondiabetic patients [2][3]

Threshold for symptoms

  • Varies greatly; , but symptoms have usually occurred by the time serum glucose concentration is < 50 mg/dL (2.8 mmol/L)
  • The threshold at which symptoms may appear in patients with chronic diabetes is especially variable due to hypoglycemia-associated autonomic failure (HAAF). [1]
    • Recurrent hypoglycemia → changes in the counterregulatory response (e.g., decreased epinephrine release) → lower glucose threshold needed to trigger symptoms → asymptomatic hypoglycemia
    • For this reason, the initial symptom of hypoglycemia in patients with HAAF is often confusion.
  • The threshold can also vary due to medication: Beta blockers can mask signs of hypoglycemia.

Signs and symptoms

Beta blockers can mask signs of hypoglycemia.

Educating patients about hypoglycemia awareness can help them to recognize the onset of autonomic symptoms and minimize the risk of severe hypoglycemia.

General diagnostic approach

  1. Confirm low blood glucose (via fingerstick or BMP) and check for Whipple triad.
  2. Rule out acute illness as a cause (e.g., infection, sepsis, burns).
  3. Review the patient's medications to rule out medication as a cause (see drugs that cause hypoglycemia).
  4. Perform diagnostic workup based on the leading differential diagnosis and whether the patient has diabetes or not.

If the Whipple triad is not confirmed, no further workup is indicated.

Diabetic patients [1]

Nondiabetic patients [2]

  • Rule out acute illness and medication as a cause.
  • Further diagnostic testing should only be pursued if the cause is not evident based on history and examination (and with the guidance of an endocrinologist).
  • The goal is to determine if the hypoglycemia is due to hyperinsulinemia (e.g., insulinoma).

Laboratory studies

72-hour fast [2]

  • Procedure: The patient fasts for 72 hours, only drinking noncaloric beverages, and all nonessential medications are discontinued.
    • Measure insulin, C-peptide, and glucose every 4–6 hours.
    • Once plasma glucose < 45 mg/dL or < 55 mg/dL with documented Whipple triad, obtain serum studies (see “Laboratory studies” above).
    • After serum studies have been obtained, continue with a glucagon tolerance test and end the fast.
    • This should be done on an inpatient basis and under the guidance of an endocrinologist.
  • Limitations
    • Results may be inaccurate if the physiological glucose level is low.
    • Rarely, insulinomas may suppress insulin release in response to hypoglycemia.
    • Insulin levels can be artificially elevated in the presence of circulating anti-insulin antibodies.

The 72-hour fast is only necessary if a spontaneous hypoglycemic episode does not occur.

Glucagon tolerance test

Interpreting the results of fasting labs and the glucagon tolerance test [1][2]

Serum levels Hypoglycemia without hyperinsulinism Hyperinsulinism (or ↑ IGF)
  • Low
  • Low
  • Low/normal
  • Elevated
Proinsulin, C peptide
  • Low/normal
  • Normal
  • Low
Glucose response to glucagon
  • Diminished response
  • Normal response

Nonsuppressed serum insulin concentrations with decreased serum C-peptide and proinsulin concentrations are consistent with exogenous insulin use.


  • If the patient is conscious:
    • Oral glucose 15–20 g
    • Fast-acting carbohydrates (such as glucose tablets, candy, or juice)
  • If the patient is unconscious (or unable to ingest glucose): [2]
    • IV dextrose
      • Subsequent dextrose infusions (D5NS or D10NS infusion) may be needed to maintain glucose levels.
      • Monitor glucose every 2 hours and titrate infusion to maintain serum glucose > 100 mg/dL.
    • IM glucagon: if neither oral or IV routes of administering glucose are feasible
    • Monitoring
      • Recheck POC glucose after 15 minutes.
      • Consider ICU admission with hourly glucose monitoring if hypoglycemia is refractory.

Suspected severe hypoglycemia should be treated immediately, without waiting for the results of blood glucose testing!

  • Treat suspected hypoglycemia with oral glucose, IV dextrose, or IM glucagon.
  • Confirm hypoglycemia (BMP).
  • Recheck glucose after 15 minutes and repeat treatment as needed.
  • Start dextrose infusion if hypoglycemia is refractory.
  • Rule out acute illness as cause.
  • Rule out medications as cause.
  • Consider further diagnostic workup if no clear cause identified.
  • Consider endocrinology consult.
  • Consider ICU admission if the patient is critically ill or requires a dextrose infusion.
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  2. Cryer et al.. Evaluation and Management of Adult Hypoglycemic Disorders: An Endocrine Society Clinical Practice Guideline. The Journal of Clinical Endocrinology & Metabolism. 2009; 94 (3): p.709-728. doi: 10.1210/jc.2008-1410 . | Open in Read by QxMD
  3. Desimone et al.. Non-Diabetic Hypoglycemia. Endotext. 2000 .
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  5. Okabayashi T. Diagnosis and management of insulinoma. World Journal of Gastroenterology. 2013; 19 (6): p.829. doi: 10.3748/wjg.v19.i6.829 . | Open in Read by QxMD
  6. Herold G. Internal Medicine. Herold G ; 2014
  7. Emanuele NV, Swade TF, Emanuele MA. Consequences of Alcohol Use in Diabetics. Alcohol Health Res World. 1998; 22 (3): p.211-219.
  8. Service FJ, Cryer PE. Hypoglycemia in adults: Clinical manifestations, definition, and causes. In: Post TW, ed. UpToDate. Waltham, MA: UpToDate. updated: June 16, 2015. Accessed: February 14, 2017.
  9. Hypoglycemia Diagnosis, A three-step approach: Whipple's Triad. Updated: May 10, 2014. Accessed: February 14, 2017.
  10. Tomky D. Detection, prevention, and treatment of hypoglycemia in the hospital. Diabetes Spectr. 2005; 18 (1): p.39-44. doi: 10.2337/diaspect.18.1.39 . | Open in Read by QxMD