The anion gap (AG) is calculated as Na+ - (Cl- + HCO3-). A patient has Na+ 138, Cl- 102, HCO3- 14, serum albumin 2 g/dL (normal 4 g/dL). The corrected anion gap reveals which type of metabolic acidosis?

• A Elevated anion gap metabolic acidosis after albumin correction ✓
• B Normal anion gap (hyperchloraemic) metabolic acidosis after albumin correction
• C Mixed elevated anion gap and normal anion gap metabolic acidosis
• D The albumin level does not affect anion gap calculation because albumin is not included in the formula

Explanation

Calculated AG = 138 - (102 + 14) = 22 mEq/L (appears borderline elevated, normal ~12 ± 2). However, albumin is the primary unmeasured anion; each 1 g/dL fall in albumin below 4 g/dL reduces AG by 2.5 mEq/L. Albumin is 2 g/dL (2 below normal), correction = +5 mEq/L. Corrected AG = 22 + 5 = 27 mEq/L, which is clearly elevated, indicating a high anion gap metabolic acidosis. Without albumin correction, the elevated AG from an organic acid might be masked by hypoalbuminemia, leading to misclassification as normal AG acidosis.

Reference: Harper's Illustrated Biochemistry, 32nd ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.