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Diabetic ketoacidosis — USMLE Step 3 MCQ

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HardEmergency MedicineDiabetic ketoacidosisUSMLE Step 3

A 29-year-old woman with type 1 diabetes presents with vomiting and Kussmaul respirations after an insulin-pump failure. Glucose is 468 mg/dL, beta-hydroxybutyrate is 7.2 mmol/L, pH is 7.12, bicarbonate is 9 mEq/L, and potassium is 2.9 mEq/L. Blood pressure improves after the first liter of crystalloid. Which treatment should occur next?

Educational content. Not a substitute for clinical judgement or local policy.

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Correct answer: B — Continue fluids and potassium; begin insulin after potassium exceeds 3.5 mEq/L

The best answer is “Continue fluids and potassium; begin insulin after potassium exceeds 3.5 mEq/L”. This is DKA with clinically important hypokalemia. Total-body potassium is depleted despite variable serum values, and insulin would drive potassium intracellularly and can trigger malignant arrhythmia. The 2024 consensus recommends fluid resuscitation and potassium replacement first, postponing insulin until potassium is above 3.5 mEq/L. Bicarbonate is not routinely indicated at this pH.

Reference: ADA/AACE Consensus Report: Hyperglycemic Crises in Adults: https://pmc.ncbi.nlm.nih.gov/articles/PMC11272983/