A 58-year-old man with nephrotic syndrome has serum albumin 2.0 g/dL and total serum calcium 8.0 mg/dL. Ionized calcium measured directly is normal. What is his corrected total calcium?

• A 7.2 mg/dL
• B 8.0 mg/dL
• C 9.6 mg/dL ✓
• D 10.4 mg/dL

Explanation

Corrected calcium = measured total calcium + 0.8 × (4 minus measured albumin). Here: 8.0 + 0.8 × (4 − 2) = 8.0 + 1.6 = 9.6 mg/dL, which is normal, matching the normal ionized level. Each 1 g/dL fall in albumin lowers measured total calcium by roughly 0.8 mg/dL without changing ionized calcium, so option B ignores the correction entirely.

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

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