A 62-year-old man with type 2 diabetes and acute stroke presents with severe hyperglycemia (glucose 850 mg/dL), serum osmolality 340 mOsm/kg, pH 7.32, and HCO₃⁻ 18 mEq/L. Serum ketones are negative. Which of the following is NOT a feature that distinguishes this presentation from pure DKA?

Explanation

## DKA vs. HHS: Key Distinguishing Features ### Clinical and Biochemical Comparison | Feature | DKA | HHS (Hyperosmolar Hyperglycemic State) | |---------|-----|----------------------------------------| | **Glucose level** | 250–600 mg/dL | >600 mg/dL (often 800–1200) | | **Serum osmolality** | 300–320 mOsm/kg | >320 mOsm/kg (often >340) | | **Arterial pH** | <7.30 (anion gap acidosis) | >7.30 (normal or hyperosmolar without acidosis) | | **HCO₃⁻** | <15 mEq/L | >15 mEq/L | | **Ketones** | Positive (high β-hydroxybutyrate) | Negative or trace | | **Anion gap** | >12 mEq/L (high anion gap) | <12 mEq/L (normal or low anion gap) | | **Primary acid-base disturbance** | **Anion gap metabolic acidosis** | **Hyperosmolar state without significant acidosis** | | **Volume depletion** | Moderate | Severe (8–10 L fluid loss) | | **Mortality** | 1–5% | 5–15% | **Key Point:** The **primary acid-base disturbance in HHS is NOT anion gap metabolic acidosis**. Instead, HHS is characterized by **hyperosmolality without significant acidosis**. The pH may be normal or even slightly elevated despite hyperglycemia because ketone production is minimal (residual insulin prevents lipolysis). ### Why This Case Is HHS, Not DKA 1. **Extreme hyperglycemia** (850 mg/dL) — typical of HHS 2. **High osmolality** (340 mOsm/kg) — hallmark of HHS 3. **Negative serum ketones** — rules out DKA 4. **pH 7.32 with HCO₃⁻ 18** — suggests **non-anion gap acidosis** (likely from volume depletion and renal insufficiency), NOT the anion gap acidosis of DKA **High-Yield:** In HHS, if acidosis is present, it is typically **non-anion gap (hyperchloremic) acidosis** from renal hypoperfusion and loss of bicarbonate, NOT the anion gap acidosis from ketoacid accumulation seen in DKA. ### The Distractor Option C states "Presence of anion gap metabolic acidosis as the primary acid-base abnormality" — this is a **feature of DKA, not HHS**. In HHS: - Anion gap is normal or low - Acidosis (if present) is non-anion gap - The primary disturbance is **hyperosmolality**, not acidosis **Clinical Pearl:** A patient with extreme hyperglycemia, high osmolality, and **negative ketones** with **normal anion gap** has HHS until proven otherwise. The absence of significant ketosis distinguishes HHS from DKA despite both presenting with severe hyperglycemia. **Mnemonic: "HHS = High glucose, High osmolality, Subtle/no ketones"** vs. **"DKA = Acidosis, Ketones, Anion gap"** [cite:Harrison 21e Ch 417]