Serum Anion Gap with Albumin Correction
Updated October 2026
The anion gap is a calculated value that helps make sense of metabolic acidosis — a state where the blood is too acidic. Your blood contains positively charged ions (mainly sodium) and negatively charged ions (mainly chloride and bicarbonate). Labs routinely measure these, but not every charged particle is measured. The anion gap estimates the "unmeasured" anions by subtracting the main measured anions from sodium: Na − (Cl + HCO₃).1
A normal gap runs about 8–12 mEq/L when potassium is left out of the calculation. Some clinicians include potassium — (Na + K) − (Cl + HCO₃) — which shifts the normal range up to roughly 10–16. This calculator supports both; enter a potassium value to include it, or leave it blank to use the more common sodium-only version.
When metabolic acidosis is present, the anion gap splits the differential into two camps. A high anion gap means unmeasured acids are accumulating — think diabetic ketoacidosis, lactic acidosis, kidney failure, or certain toxic ingestions. A normal gap acidosis points instead toward bicarbonate loss, as in severe diarrhea or certain kidney conditions. That fork in the road is why the anion gap is one of the first things calculated when acidosis appears on a metabolic panel.2
Albumin is itself a negatively charged protein and a major contributor to the "normal" gap. When albumin is low — common in critically ill patients — the baseline gap falls, and a dangerously high-gap acidosis can hide inside a deceptively normal-looking number. The correction adds roughly 2.5 mEq/L to the gap for every 1 g/dL that albumin sits below 4.0. Enter an albumin value and this calculator shows the corrected gap, which can unmask hidden acidosis. For patients with low albumin, this adjustment is genuinely important.
The anion gap is a pointer, not an answer. A high gap tells you to go looking for an unmeasured acid; it doesn't say which one. Interpreting it sits within a full acid-base assessment alongside pH, bicarbonate, the clinical picture, and often a check of kidney function. This tool does the arithmetic accurately; the diagnosis belongs to a clinician.
In critically ill or low-albumin patients, always enter albumin. The corrected gap can reveal a high-gap acidosis that the raw number hides.
Pick one formula and stick with its range: 8–12 for the sodium-only version, 10–16 if you include potassium. Mixing them up is the most common interpretation error.
A high gap is a starting point, not a diagnosis. It tells you an unmeasured acid is present — the next step is identifying which one, alongside the full clinical picture.
Use electrolytes from a single panel, and interpret the gap together with pH and bicarbonate. The anion gap is one piece of a complete acid-base assessment.