A patient in diabetic ketoacidosis has measured serum sodium of 128 mEq/L and blood glucose of 600 mg/dL. What is the corrected serum sodium?

• A 128 mEq/L
• B 132 mEq/L
• C 136 mEq/L ✓
• D 144 mEq/L

Explanation

Hyperglycemia draws water into the extracellular compartment and dilutes sodium. Using the conventional correction of 1.6 mEq/L per 100 mg/dL of glucose above 100: 128 + 1.6 x 5 = 136 mEq/L, indicating near-normal tonicity rather than true hyponatremia. Option B underestimates the correction, and option D would require a correction factor far larger than any accepted formula provides.

Reference: Harrison's Principles of Internal Medicine, 21st ed.

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