Anion gap (with albumin correction)

The unmeasured-anion window: Na − Cl − HCO3, corrected upward by 2.5 mmol/L for every 10 g/L of albumin below 40.

Sodium(mmol/L)Chloride(mmol/L)Bicarbonate(mmol/L)Albumin (optional, 40 if blank)(g/L)

Result

Fill the inputs to compute.

Interpretation: Roughly 4 to 12 mmol/L is expected. An elevated gap means unmeasured anions: lactate, ketones, toxins, uremia.
Limitations: Normal ranges depend on the analyzer. Hypoalbuminemia hides real gaps, which is what the correction repairs.
Reference: Figge J et al. Anion gap and hypoalbuminemia. Crit Care Med 1998;26:1807-10.

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