Hypoglycemia Summary

Hypoglycemia Definition

  • Hypoglycemia is defined as a blood glucose concentration below the fasting value.
  • The most widely suggested cutoff is 50 mg/dL (2.8 mmol/L), but some suggest 60 mg/dL (3.3 mmol/L).

Symptoms of Hypoglycemia

  • Symptoms vary among individuals.
  • Epinephrine produces classic signs: trembling, sweating, nausea, rapid pulse, lightheadedness, hunger, and epigastric discomfort.
  • Rapid decrease in blood glucose may trigger symptoms even if glucose levels are not hypoglycemic.
  • Very low glucose concentrations (<20 30 or mg/dL; <1.1 1.7 mmol/L) cause severe CNS dysfunction (Neuroglycopenia).

Causes of Hypoglycemia

  • Can be classified by age of onset.

  • Neonates:

    • Lower glucose concentrations than adults (mean <35 mg/dL; <2.0 mmol/L).
    • Common causes: prematurity, maternal diabetes, gestational diabetes mellitus, eclampsia.

  • Adults:

    • May result from decreased hepatic glucose production or increased glucose use.
    • Symptoms usually begin below 55 mg/dL (3.1 mmol/L), cerebral impairment below 50 mg/dL (2.8 mmol/L).

Fasting Hypoglycemia in Adults

  • Drugs: Pentamidine, gatifloxacin, quinine, oral hypoglycemic agents, ethanol.
  • Hepatic failure: Impaired gluconeogenesis or glycogen storage.
  • Hormonal deficiency: Growth hormone, glucocorticoids, thyroid hormone, or glucagon deficiency.
  • Insulin-producing pancreatic islet cell tumor: High insulin with low glucose.
    • Diagnostic criteria when fasting plasma glucose is below 55 mg/dL (3.1 mmol/L):
    • Plasma insulin >= 18 pmol/L
    • Plasma C-peptide >= 0.2 nmol/L
    • Plasma proinsulin >= 5.0 pmol/L
  • Spontaneous production of antibodies to insulin: Low C-peptide, very high insulin.
  • Non-pancreatic neoplasms: Overuse glucose or produce insulin-like growth factor (IGF) 2.
  • Septicemia: Depleted glycogen, impaired gluconeogenesis.
  • Renal failure: Occurs in end-stage renal failure.

Postprandial Hypoglycemia

  • Occurs in the fed state; may be due to drugs, antibodies to insulin/receptor, or inborn errors.
  • Reactive hypoglycemia (functional hypoglycemia): No scientific evidence supports its existence.
  • Whipple’s triad: Low blood glucose with typical symptoms alleviated by glucose administration.

Hypoglycemia in Diabetes Mellitus

  • Common in type 1 and type 2 diabetes.
  • Two main mechanisms:
    • Defective glucose counterregulation: Impaired glucagon and epinephrine response.
    • Hypoglycemia unawareness: Reduced or absent neurogenic warning symptoms.

Evaluation of Hypoglycemia

  • Evaluate only if Whipple triad is documented.
  • Prolonged fast (up to 72 hours) in a hospital setting.
  • Blood samples every 6 hours for glucose, insulin, C-peptide