Anion Gap Calculator – Formula & Albumin Correction

This calculator uses the common serum formula without potassium: anion gap = sodium − (chloride + bicarbonate/chemistry total CO₂). The result is derived arithmetic, not a directly measured analyte.

Sources: [1, 2]

No. This page uses the sodium-only formula. Potassium-inclusive results are numerically different and must be compared with a potassium-inclusive reference interval; the calculator does not mix the two definitions.

Sources: [1, 6]

There is no single universal interval for every laboratory and method. Historical and contemporary published examples differ, so compare the result with the interval supplied by the laboratory that measured the electrolyte panel. This calculator does not assign a dynamic normal category.

Sources: [6, 7, 8]

A value above the source laboratory's interval can reflect additional unmeasured anions, but it does not by itself establish acidemia, metabolic acidosis, cause, or severity. Direct measurements and the wider clinical record remain necessary.

Sources: [3, 9]

The term applies only after metabolic acidosis has been independently established. Broad mechanisms include gastrointestinal bicarbonate loss, especially diarrhea; renal tubular acidosis; and chloride-associated states such as chloride loading or other bicarbonate–chloride balance disturbances. Mixed disorders occur, and a normal-range serum gap is not a diagnosis by itself.

Sources: [3, 9]

Published explanations include measurement error, hypoalbuminemia, positively charged proteins or other cations, chloride overestimation, and sodium underestimation. An unexpected result should be confirmed and interpreted with its laboratory context; the number does not identify a cause.

Sources: [8]

Albumin is an important unmeasured anion. Hypoalbuminemia lowers the observed gap and may mask an increase in other unmeasured anions, which is why the optional albumin-adjusted value is shown separately from the raw result.

Sources: [3, 4]

The optional Figge 2.5 calculation is adjusted AG = raw AG + 2.5 × (4 − albumin in g/dL). It is a formula-derived estimate, not a direct measurement or a universally applicable correction.

Sources: [3, 4]

Chemistry total CO₂ is mostly bicarbonate, while blood-gas bicarbonate is generally calculated from pH and PCO₂. They are related but not completely interchangeable; use a clinically coherent chemistry state rather than combining unrelated samples or times.

Sources: [5]

No. Serum AG here is serum Na − (serum Cl + serum HCO₃/total CO₂). Urine AG is urine Na + urine K − urine Cl. They use different specimens, answer different clinical questions, and are not interchangeable; the separate Urine Anion Gap calculator handles the urine calculation.

Sources: [2, 9]