Hyperosmolar Hyperglycemic State
Endocrinology
Illness script · Endocrinology
Hyperosmolar Hyperglycemic State
Life-threatening diabetic emergency with extreme hyperglycemia, profound dehydration, and hyperosmolality WITHOUT significant ketoacidosis.
This illness script for Hyperosmolar Hyperglycemic State covers predisposing factors, classic presentation, mechanism, workup, management, and the clinical pivots that separate it from look-alikes—written for USMLE Step 1 and clerkship reasoning.
01
Predisposing factors
- Type 2 DM (classic); rare in T1DM
- Elderly patients with limited thirst/access to fluids
- Precipitants: infection (#1), MI, stroke, medications (steroids, thiazides, antipsychotics)
- Poor medication compliance or new-onset T2DM
- Renal insufficiency impairing glucose clearance
02
Presentation
- Insidious onset over days to weeks (slower than DKA)
- Extreme hyperglycemia (glucose often >600 mg/dL, frequently >1000)
- Profound dehydration: tachycardia, hypotension, dry mucous membranes
- Altered mental status, stupor, or coma (correlates with degree of hyperosmolality)
- Focal neurologic signs or seizures possible; Kussmaul breathing absent
- Minimal or no nausea/vomiting (contrast with DKA)
03
Pathophysiology
- Enough residual insulin to suppress lipolysis/ketogenesis, but insufficient to control glucose
- Severe hyperglycemia → osmotic diuresis → massive free water loss (8–12 L deficit)
- Serum osmolality rises >320 mOsm/kg, causing cellular dehydration and neurologic dysfunction
- No significant anion-gap acidosis (distinguishes from DKA)
04
Diagnostics
- Glucose >600 mg/dL (often 900–1200); DKA threshold is typically >250
- Serum osmolality >320 mOsm/kg (calculated: 2[Na] + glucose/18 + BUN/2.8)
- pH >7.3, bicarbonate >18 mEq/L, minimal/no ketonemia — key DKA differentiator
- BMP, urinalysis, cultures, ECG, CXR to identify precipitant
- Corrected Na: add 1.6 mEq/L Na per 100 mg/dL glucose above 100
05
Management
- Aggressive IV fluid resuscitation: normal saline first (1–2 L/hr initially), then 0.45% NaCl
- Replace free water deficit slowly (correct over 24–48 h to avoid cerebral edema)
- Insulin: start ONLY after fluids initiated and K+ ≥3.5 mEq/L; lower rate than DKA
- Potassium repletion: hypokalemia develops as glucose/insulin drive K+ intracellularly
- Identify and treat precipitating cause; ICU admission; mortality 5–20%
06
Clinical pivots
How to separate this script from the look-alikes that show up on exams and on the wards.
Diabetic Ketoacidosis
DKA has pH <7.3, anion-gap acidosis, ketosis, Kussmaul breathing; HHS has none of these
Hypoglycemic coma
Glucose is critically LOW in hypoglycemia; HHS glucose is extremely HIGH (>600)
Nonketotic hyperosmolar state from other cause (e.g., enteral feeds)
HHS requires known/new DM context; other hyperosmolar states lack hyperglycemia as driver
Alcoholic ketoacidosis
AKA has ketosis with normal or low glucose and ethanol history, not extreme hyperglycemia
Keep reading
Full library- HyperkalemiaSerum potassium >5.5 mEq/L causing life-threatening cardiac and neuromuscular dysfunction via altered membrane potential.
- Infective EndocarditisMicrobial infection of native or prosthetic heart valves producing vegetations, bacteremia, and systemic embolic phenomena.
Educational use only. This illness script is a study framework, not medical advice. Confirm decisions with current guidelines and your clinical supervisors.