The serum anion gap needs to be adjusted for changes in serum albumin. Hypoalbuminemia can mask a significant metabolic acidosis.

observed anion gap =

= ((sodium in mEq/L) + (potassium in mEq/L)) - ((chloride in mEq/L) + (HCO3 in mEq/L))


corrected anion gap =

= (observed anion gap) + (0.25 * ((normal serum albumin in g/L) – (observed albumin in g/L)) =

= (observed anion gap) + (0.25 * (44 – (observed albumin in g/L))



• The molecular weight of albumin is 66,500.

• 44 g/L albumin is 0.66 mmol/L.

• Albumin has a high negative charge, so the mEq/L = (mmol/L) * (number of negative charge). According to Jurado et al, 1 mmol/L albumin is 18 mEq/L. So 44 g/L albumin is equivalent to 11.9 mEq/L. Each reduction of 1 g/dL (10 g/L) reduces anion gap by 2.5 mEq/L.

• I am not sure if the same equation can be used with hyperalbuminemia.

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