A critically ill patient has Na 136 mEq/L, Cl 104 mEq/L, HCO3 24 mEq/L, glucose 110 mg/dL and albumin 1.6 g/dL. What is the ALBUMIN-CORRECTED anion gap?

• A 8 mEq/L, indicating no occult metabolic acidosis
• B 2 mEq/L, indicating laboratory error
• C 20 mEq/L, indicating high anion gap acidosis
• D 14 mEq/L, indicating an unmeasured anion process ✓

Explanation

The calculated anion gap is 136 minus (104 plus 24), which is 8 mEq/L. Each 1 g/dL fall in albumin below 4 g/dL lowers the observed gap by about 2.5 mEq/L because albumin is an unmeasured anion. Correction adds 2.5 times (4 minus 1.6), that is 6, giving a corrected gap of 14 mEq/L. Without correction a genuine lactic or ketoacidosis would be masked by hypoalbuminaemia, a common trap in malnourished and cirrhotic surgical patients.

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

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