Adjustment of Anion Gap (AG) for albumin

Adjustment of Anion Gap (AG) for albumin

A big majority of patients particularly in medical-ICU are hypoalbumenic

Albumin is a major unmeasured anion and its lower level may give false normal anion gap (means normal calculated anion gap despite actual high anion gap).

The formula to adjust anion gap with albumin is as follows:

Adjusted AG = calculated AG + 2.5 (4.5 - measured albumin)
Calculated AG = Na - (Cl + HCO3)
4.5 = normal albumin level

Example: Patient has following data:
Na = 144
Cl = 102
HCO3 = 18
Albumin = 2.6

Calculated AG = 144 - (102 + 18) = 24 mEq/L
Adjusted AG = 24 + 2.5 (4.5 - 2.6) = 24 + 2.5(1.9) = 28.75 mEq/L

Reference:

Anion gap and hypoalbuminemia - Critical Care Medicine. 26(11):1807-1810, November 1998.