Anion Gap (Albumin-Corrected)
Anion gap calculation for differential diagnosis of metabolic acidosis.
Updated · Methodology
About this calculator
The anion gap is the difference between measured cations and anions in plasma. It reflects unmeasured anions (phosphates, sulfates, proteins, organic acids). Formula: AG = Na – (Cl + HCO3). Normal range – 8-12 mmol/L. With hypoalbuminemia an albumin-corrected value is used: AG corrected = AG + 2.5 × (4.4 – albumin g/dL). Clinical application. Differential diagnosis of metabolic acidosis. Elevated AG (>12) – accumulation of unmeasured anions: lactic acidosis (sepsis, shock, metformin), ketoacidosis (diabetic, alcoholic, starvation), ethylene glycol, methanol, salicylate poisoning, uremia, rhabdomyolysis. Normal AG – bicarbonate loss: diarrhea, renal tubular acidosis, carbonic anhydrase inhibitors. Delta gap. For diagnosis of mixed acid-base disorders use delta-gap: (AG – 12) / (24 – HCO3). Around 1 – pure high AG acidosis. >2 – concurrent metabolic alkalosis. <0.4 – concurrent normal AG acidosis. Limitations. Lithium, bromide, iodide can falsely lower AG. Hypoalbuminemia drops baseline by about 2.5 mmol/L per 1 g/dL albumin deficit – without correction, true AG can be missed in septic and oncology patients.
Source
Emmett M, Narins RG. Clinical use of the anion gap. Medicine (Baltimore). 1977;56(1):38-54.
Formula version: 2024-v1
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