Diabetic ketoacidosis — USMLE Step 2 CK MCQ

Correct answer: A — Begin potassium replacement and defer insulin until potassium exceeds 3.5 mEq/L

Although total-body potassium is depleted in diabetic ketoacidosis, the initial serum concentration may be normal or high because insulin deficiency and acidosis shift potassium extracellularly. This patient is already hypokalemic at 3.1 mEq/L. Insulin would drive potassium into cells and could precipitate life-threatening arrhythmia and respiratory muscle weakness. Current consensus guidance recommends beginning potassium replacement and delaying insulin until the serum potassium is above 3.5 mEq/L, with frequent monitoring. Isotonic fluid resuscitation continues while potassium is corrected. Routine bicarbonate is not indicated unless acidosis is extreme, and it can worsen hypokalemia. Dextrose is generally added later when glucose falls below the treatment threshold so insulin can continue until ketoacidosis resolves; it is not a reason to stop fluids. Long-acting subcutaneous insulin alone cannot replace controlled acute fluid, electrolyte and insulin management.

Reference: American Diabetes Association et al. Hyperglycemic Crises in Adults With Diabetes: A Consensus Report. Diabetes Care. 2024. https://diabetesjournals.org/care/article/47/8/1257/156808/Hyperglycemic-Crises-in-Adults-With-Diabetes-A