Anion Gap Calculator

The anion gap estimates the difference between unmeasured serum cations and anions, helping to identify the underlying cause of metabolic acidosis. The standard formula is expressed as Anion Gap = [Na⁺] - ([Cl⁻] + [HCO₃⁻]), though some clinical settings incorporate potassium by using Anion Gap = [Na⁺] + [K⁺] - ([Cl⁻] + [HCO₃⁻]). Because abnormal serum albumin levels can artificially skew these results, a corrected anion gap is frequently calculated using the formula: Corrected AG = Anion Gap + 2.5 × (4.4 - Albumin), assuming a standard albumin concentration of 4.4 g/dL.

Consider a patient with the following basic metabolic panel and albumin laboratory results: Sodium ([Na⁺]) = 140 mEq/L, Chloride ([Cl⁻]) = 104 mEq/L, Bicarbonate ([HCO₃⁻]) = 22 mEq/L, and Serum Albumin = 2.4 g/dL. First, compute the standard anion gap: 140 - (104 + 22) = 140 - 126 = 14 mEq/L. Next, adjust for the low albumin level using the correction formula: 14 + 2.5 × (4.4 - 2.4) = 14 + 2.5 × (2.0) = 14 + 5.0 = 19 mEq/L. This reveals a significantly elevated corrected anion gap that might have been hidden by hypoalbuminemia.

Always verify the units of your laboratory measurements before running the calculation to avoid compounding errors. Keep in mind that hypoalbuminemia can mask high anion gap metabolic acidosis, making the albumin-corrected anion gap calculation an essential step for accurate diagnosis. Finally, remember that calculators serve as supplementary aids and must always be interpreted within the full context of a patient's clinical presentation and history.