A 55-year-old man with diabetic ketoacidosis has blood glucose of 600 mg/dL and serum Na+ of 128 mEq/L. Using the standard correction factor, what is the approximate corrected serum sodium level?

• A 128 mEq/L (no correction needed)
• B 136 mEq/L
• C 120 mEq/L
• D 140 mEq/L ✓

Explanation

The standard correction factor is that serum Na+ decreases by 1.6 mEq/L for every 100 mg/dL rise in glucose above normal. Here glucose is elevated by 500 mg/dL, so Na+ falls by approximately 8 mEq/L. Corrected Na+ = 128 + 8 = 136 mEq/L. Some references use 2.4 mEq/L per 100 mg/dL, which would give 140 mEq/L. The widely taught Indian exam convention uses 1.6 mEq/L, making 136 the expected answer.

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

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