Endocrinology · PANCE / PANRE

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

Hypoglycemia workup — critical sample interpretation (drawn AT the time of documented low glucose).

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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