Causes of Hypoglycemia in Adults
Drugs are the most common cause of hypoglycemia in adults without diabetes, with insulin and insulin secretagogues being the primary offenders, followed by alcohol. 1
Primary Etiologic Categories
The Endocrine Society Clinical Practice Guideline 1 provides a systematic framework for understanding hypoglycemia causes:
1. Drug-Induced Hypoglycemia (Most Common)
- Insulin and insulin secretagogues (sulfonylureas, meglitinides) in diabetic patients account for 90% of episodes in this population 2
- Alcohol - impairs gluconeogenesis 1, 3
- Other medications that can precipitate hypoglycemia
- Iatrogenic causes during treatment of hyperkalemia or total parenteral nutrition 2
Clinical Pitfall: In hospitalized diabetic patients, hypoglycemia frequently occurs due to decreased caloric intake related to illness or hospital routine, not just excessive insulin dosing 2.
2. Critical Illnesses
- Sepsis and severe infections 1, 4
- Renal failure - second most frequent diagnosis after drugs; present in 49% of hospitalized hypoglycemic patients 2
- Hepatic failure 1, 3
- Shock states
- Burns
- Cardiac insufficiency 3
3. Hormone Deficiencies
- Cortisol deficiency (including hypopituitarism) 1, 5
- Glucagon deficiency 5
- Other endocrine insufficiencies 3
4. Endogenous Hyperinsulinism (Rare)
- Insulinoma - inappropriate insulin secretion from pancreatic β-cell tumor 1, 3
- Noninsulinoma pancreatogenous hypoglycemia syndrome (NIPHS) 1
- Genetic causes:
5. Non-Islet Cell Tumors
- NICTH (Non-Islet-Cell Tumor Hypoglycemia) - large tumors secreting Big-IGF2 5, 3
- Characterized by low insulin, C-peptide, and IGF-1 levels 5
6. Autoimmune Causes (Rare)
- Insulin autoantibodies (Hirata syndrome) - especially with Graves' disease 5, 3
- Insulin receptor antibodies 5, 3
7. Post-Surgical
- Post-gastric bypass/bariatric surgery - can cause both fasting and postprandial hypoglycemia 1
- Post-gastrectomy reactive hypoglycemia 3
- Pancreas transplantation 5
8. Inborn Errors of Metabolism (IEM)
These may present in adulthood 5:
- Fasting hypoglycemia: Glycogen storage disorders (types 0, I, III), fatty acid oxidation defects, gluconeogenesis disorders
- Postprandial hypoglycemia: Hereditary fructose intolerance
- Associated findings: rhabdomyolysis, hepatomegaly, cardiomyopathy
9. Factitious/Surreptitious Hypoglycemia
10. Multifactorial (Underdiagnosed)
- Common in hospitalized, underfed elderly patients with severe disease 3
- Associated with 27% hospital mortality when present 2
Diagnostic Algorithm Framework
The guideline 1 recommends this systematic approach:
Step 1: Review history, physical findings, and laboratory data for clues to specific disorders—drugs first, then critical illnesses, hormone deficiencies, and tumors.
Step 2: In seemingly well individuals, during a spontaneous hypoglycemic episode, measure:
- Plasma glucose, insulin, C-peptide, proinsulin, β-hydroxybutyrate
- Screen for oral hypoglycemic agents
- Measure insulin antibodies
- Observe glucose response to 1.0 mg IV glucagon
Step 3: If spontaneous episodes cannot be observed, recreate circumstances with supervised 72-hour fast or mixed meal challenge.
Critical Laboratory Thresholds for Endogenous Hyperinsulinism 1:
- Glucose <55 mg/dL (3.0 mmol/L)
- Insulin ≥3.0 μU/mL (18 pmol/L)
- C-peptide ≥0.6 ng/mL (0.2 nmol/L)
- Proinsulin ≥5.0 pmol/L
- β-hydroxybutyrate ≤2.7 mmol/L
Important Clinical Context
Mortality Association: Hypoglycemia correlates with high mortality in severely ill patients (27% hospital mortality), related to both the degree of hypoglycemia and number of risk factors 2, 4. This reflects disease severity rather than direct causation in most cases.
Timing Matters: The relationship to meals helps narrow the differential—fasting hypoglycemia suggests different etiologies (insulinoma, metabolic disorders, hormone deficiencies) than postprandial hypoglycemia (post-bariatric surgery, genetic hyperinsulinism, reactive causes) 5.