Acid-Base & ElectrolytesEvidence-Based Golden Standard
Serum Anion Gap & Albumin-Corrected Anion Gap
Calculates serum anion gap with Figge albumin correction to unmask occult high-anion-gap metabolic acidosis in hypoalbuminemia.
AG = Na⁺ - (Cl⁻ + HCO₃⁻)
Corrected AG = AG + 2.5 × (4.0 - Albumin [g/dL])
Published Clinical Benchmark Cases
Clinical Parameters & Inputs
Unit: mEq/L
mEq/L
Unit: mEq/L
mEq/L
Unit: mEq/L
mEq/L
Unit: g/dL
g/dL
Normal: 4.0 g/dL (40 g/L). Hypoalbuminemia lowers the baseline normal AG by ~2.5 mEq/L per 1 g/dL drop.
Computed OutputNormal AG
12mEq/L
Diagnostic Interpretation
Normal Anion Gap (12 mEq/L). If metabolic acidosis is present, suspect Normal Anion Gap Metabolic Acidosis (NAGMA/hyperchloremic) such as diarrhea, renal tubular acidosis (RTA), ureteral diversion, or normal saline resuscitation.
Calculation Breakdown
Uncorrected Anion Gap
140 - (104 + 24) =12 mEq/L
Figge Albumin Correction
12 + 2.5 × (4.0 - 4) =12 mEq/L
Albumin dropped by 0 g/dL below reference normal of 4.0 g/dL.
Clinical Decision Pearls
- Always evaluate serum albumin when interpreting anion gap. For every 1.0 g/dL decrease in serum albumin, expected "normal" anion gap decreases by 2.5 mEq/L.
- A "normal" uncorrected AG of 11 in a critically ill patient with serum albumin 1.5 g/dL represents an occult HAGMA with corrected AG of 17.25 mEq/L.
- If corrected AG is elevated, immediately proceed to calculate the Delta-Delta ratio to check for mixed metabolic disorders.
Limitations & Confounders
- Severe hyperkalemia or profound hypercalcemia mildly blunts the anion gap.
- Immunoassay interference (e.g. bromide or iodide measured as chloride) can create pseudonegative anion gap.
Evidence & Citations
- Figge J, et al. Anion gap and hypoalbuminemia. Crit Care Med. 1998;26(11):1807-1810.
- Kraut JA, Madias NE. Serum anion gap: its uses and limitations in clinical medicine. Clin J Am Soc Nephrol. 2007;2(1):162-174.