A normal anion gap calculation can mask dangerous metabolic acidosis if clinicians overlook circulating protein levels. Serum albumin represents the vast majority of normal unmeasured anions. Each gram of albumin carries multiple negative electrical charges.
When a patient experiences malnutrition, cirrhosis, severe nephrotic syndrome, or systemic inflammatory response syndrome, serum albumin drops. For every 1.0 g/dL reduction in serum albumin below the baseline of 4.0 g/dL, the baseline AGAP drops by roughly 2.3 to 2.5 mEq/L.
$$\text{Adjusted AGAP} = \text{Calculated AGAP} + 2.5 \times (4.0 - \text{Serum Albumin in g/dL})$$
Consider an intensive care patient with a calculated AGAP of 10 mEq/L and an albumin level of 1.5 g/dL. On paper, 10 mEq/L appears completely normal. Applying the hypoalbuminemia correction reveals an adjusted gap of $10 + 2.5 \times (4.0 - 1.5) = 16.25\text{ mEq/L}$. Without accounting for protein levels, life-threatening lactic acidosis or occult sepsis can hide in plain sight behind deceptively normal numbers.
