A 22-year-old man with type 1 diabetes presents with diabetic ketoacidosis: glucose 540 mg/dL, pH 7.12, bicarbonate 8 mEq/L, ketones strongly positive, and serum potassium 3.1 mEq/L on admission. What is the correct immediate step regarding insulin therapy?
- A Start regular insulin IV bolus of 0.1 U/kg immediately along with saline
- B Give subcutaneous glargine first, then start the infusion
- C Withhold insulin until serum potassium is corrected above 3.3 mEq/L ✓
- D Start insulin only after the anion gap normalises
Correct answer: C. Withhold insulin until serum potassium is corrected above 3.3 mEq/L
Explanation
In DKA with hypokalaemia, insulin drives potassium into cells and can precipitate fatal arrhythmias or respiratory muscle weakness. Standard protocol gives 20 to 30 mEq potassium per litre of fluids and defers insulin until potassium exceeds 3.3 mEq/L. The distractor C-killer is option A: a bolus in this setting is specifically contraindicated because total body potassium is depleted even when the measured value is only mildly low.
Reference: Harrison's Principles of Internal Medicine, 21st ed.
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