Hypoglycemia
Plasma glucose low enough to cause neuroglycopenic or autonomic symptoms; medical emergency if severe.
Also known as: hypoglycemia, low blood sugar, insulin reaction, neuroglycopenia
Overview
Plasma glucose level sufficiently low to produce symptoms or impair physiologic function. ADA Level 1: glucose <70 mg/dL (alert value); Level 2: <54 mg/dL (clinically significant); Level 3: severe event requiring external assistance for recovery regardless of glucose value.
Epidemiology
Most common acute complication of insulin therapy. In T1DM, average ~2 symptomatic episodes per week and 1 severe event per year. Severe hypoglycemia affects ~25% of insulin-treated T2DM patients annually. Increases mortality and is associated with cognitive decline.
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Risk factors
- Insulin or sulfonylurea therapy (most common iatrogenic cause)
- Missed meals, exercise without carb adjustment, alcohol use
- Renal or hepatic impairment (reduced insulin/sulfonylurea clearance)
- Adrenal insufficiency, hypopituitarism
- Tight glycemic control with A1c <6%
- Hypoglycemia unawareness (prior episodes blunt autonomic response)
- Sepsis, malignancy, post-bariatric surgery
- Insulinoma, factitious (surreptitious insulin or sulfonylurea use)
Pathophysiology
Glucose is the obligate fuel of the CNS. When plasma glucose falls below ~70 mg/dL, insulin secretion suppresses, then glucagon and epinephrine rise (autonomic symptoms). Below ~54 mg/dL, cortisol and growth hormone respond, and neuroglycopenia develops. Repeated hypoglycemia blunts the counter-regulatory response, producing hypoglycemia unawareness.
Clinical presentation
Symptoms
- Autonomic (early, glucose ~55-70): tremor, palpitations, anxiety, sweating, hunger, paresthesias
- Neuroglycopenic (lower, <54): confusion, slurred speech, behavioral change, vision blur, weakness, seizure, coma
- Whipple triad: (1) symptoms consistent with hypoglycemia, (2) low measured glucose, (3) resolution after glucose administration
Signs / physical exam
- Diaphoresis, pallor, tachycardia, tremor
- Decreased mental status, focal neurologic deficits (can mimic stroke)
- Hypothermia in prolonged severe episodes
- Seizure activity, posturing in severe cases
Classic findings
Insulin-treated diabetic with sudden diaphoresis, tremor, and confusion that resolves rapidly after oral glucose or IV dextrose.
Differential diagnosis
- Insulinoma — Recurrent fasting hypoglycemia with documented elevated insulin AND C-peptide AND proinsulin; localizing imaging (EUS, MRI); Whipple triad
- Factitious hypoglycemia (insulin) — Elevated insulin with LOW C-peptide; access to insulin (healthcare worker, relative of diabetic)
- Sulfonylurea ingestion (accidental or surreptitious) — Elevated insulin AND C-peptide; positive urine sulfonylurea screen; differentiates from insulinoma
- Adrenal insufficiency — Fatigue, hyperpigmentation, hyponatremia, hyperkalemia; low AM cortisol, abnormal cosyntropin stim
- Reactive (postprandial) hypoglycemia — Symptoms 2-4 h post-meal, especially after gastric bypass; OGTT or mixed-meal tolerance test reproduces; insulin/C-peptide appropriately suppressed
- Non-islet cell tumor hypoglycemia — Large mesenchymal tumors producing big IGF-2; low insulin, low C-peptide, elevated IGF-2:IGF-1 ratio
- Alcohol-induced — Heavy intake without food; impaired gluconeogenesis; treat with glucose + thiamine
- Seizure, stroke, syncope (mimics) — Neurologic events without low glucose; check fingerstick in any acute neurologic presentation
Diagnostic workup
Diagnostic criteria
Documented hypoglycemia (Whipple triad). Etiologic differentiation requires the critical sample: elevated insulin + elevated C-peptide → endogenous (insulinoma, sulfonylurea); elevated insulin + low C-peptide → exogenous insulin; low insulin + low C-peptide + elevated IGF-2 → non-islet cell tumor.
Labs
- POC fingerstick glucose — confirm low value before treating in non-emergent setting
- Serum glucose to confirm
- If etiology unclear, draw a 'critical sample' at the time of hypoglycemia: insulin, C-peptide, proinsulin, beta-hydroxybutyrate, sulfonylurea screen, cortisol, growth hormone
- BMP, LFTs, TSH (rule out adrenal, hepatic, hypothyroid contribution)
- Consider 72-hour supervised fast for insulinoma workup if no other cause identified
Imaging
- Not needed for acute event
- CT, MRI, or endoscopic ultrasound for insulinoma localization once biochemical diagnosis confirmed
- Selective arterial calcium stimulation testing if imaging negative
Diagnostic algorithm
| Etiology | Insulin | C-peptide | Proinsulin | β-OHB | Sulfonylurea screen |
|---|---|---|---|---|---|
| Insulinoma | High | High | High | Low | Negative |
| Sulfonylurea (oral hypoglycemic) | High | High | Normal/high | Low | Positive |
| Exogenous insulin (factitious) | High | LOW (suppressed) | Low | Low | Negative |
| Non-islet cell tumor (IGF-2) | Low | Low | Low | Low | Negative |
| Adrenal insufficiency | Low | Low | Low | Elevated | Negative |
| Alcohol / starvation | Low | Low | Low | Elevated | Negative |
Complications
- Seizure, coma, anoxic brain injury, death (especially nocturnal episodes)
- Cardiovascular events: arrhythmia (QT prolongation), MI, sudden cardiac death — 'dead-in-bed' syndrome
- Cognitive decline with recurrent severe episodes
- Trauma from falls or motor vehicle accidents
- Hypoglycemia unawareness — perpetuates the cycle
- Anxiety, fear of hypoglycemia leading to deliberate hyperglycemia
PANCE pearls
- Whipple triad confirms true hypoglycemia — don't chase asymptomatic 'low' readings on CGM or fingerstick in non-diabetics.
- Critical sample drawn at the time of low glucose is the highest-yield test for diagnostic workup — once glucose normalizes, hormone levels lose interpretability.
- Glyburide is long-acting and renally cleared — admit ALL elderly or CKD patients with glyburide-induced hypoglycemia for at least 24 hours.
- Octreotide suppresses sulfonylurea-induced insulin release and is the antidote of choice for refractory sulfonylurea hypoglycemia.
- Recurrent fasting hypoglycemia in a non-diabetic is insulinoma until proven otherwise.
References
- ADA 2025 — American Diabetes Association Standards of Care in Diabetes—2025: Glycemic Goals and Hypoglycemia (Diabetes Care 2025; 48 Suppl 1)
- Endocrine Society 2009 — Evaluation and Management of Adult Hypoglycemic Disorders: An Endocrine Society Clinical Practice Guideline (Cryer et al., J Clin Endocrinol Metab 2009)
- ADA/EASD 2017 — International Hypoglycaemia Study Group: Glucose Concentrations of Less than 3.0 mmol/L Should Be Reported in Clinical Trials
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