Anion Gap Calculator

Formula

AG = Na - (Cl + HCO3) | Corrected AG = AG + 2.5 × (4.0 - Albumin) | Delta Ratio = (Corrected AG - 12) / (24 - HCO3)

The anion gap measures unmeasured anions. Normal AG is 8-12 mEq/L. Corrected AG adjusts for hypoalbuminemia (2.5 mEq/L per 1 g/dL below 4.0). The delta-delta ratio identifies mixed acid-base disorders: <1 = concurrent NAGMA, 1-2 = pure HAGMA, >2 = concurrent metabolic alkalosis.

Worked Examples

Example 1: Normal Anion Gap

Problem: Na 140, Cl 103, HCO3 24, Albumin 4.0 g/dL.

Solution: AG = 140 - (103 + 24) = 13\nCorrected AG = 13 + 2.5(4.0 - 4.0) = 13\nNormal AG (close to upper limit)\nNo HAGMA

Result: AG 13, Corrected AG 13 — Normal, no metabolic acidosis

Example 2: DKA with HAGMA

Problem: Na 138, Cl 98, HCO3 10, Albumin 3.0 g/dL.

Solution: AG = 138 - (98 + 10) = 30\nCorrected AG = 30 + 2.5(4.0 - 3.0) = 32.5\nDelta ratio = (32.5 - 12)/(24 - 10) = 1.46\nPure HAGMA (ratio 1-2)

Result: AG 30, Corrected AG 32.5 — HAGMA, delta ratio 1.46 (pure HAGMA)

Frequently Asked Questions

What is the anion gap?

The anion gap is the difference between measured cations (sodium) and measured anions (chloride + bicarbonate) in the blood. It represents unmeasured anions such as albumin, phosphate, sulfate, and organic acids. The normal anion gap is approximately 8-12 mEq/L (when not corrected for albumin). An elevated anion gap indicates accumulation of unmeasured acids, as seen in conditions like DKA, lactic acidosis, and toxic ingestions.

What causes a high anion gap metabolic acidosis?

The mnemonic MUDPILES helps remember causes: Methanol, Uremia, Diabetic ketoacidosis (DKA), Propylene glycol, Isoniazid/Iron, Lactic acidosis (type A from tissue hypoperfusion, type B from medications or metabolic causes), Ethylene glycol, Salicylates. Other causes include starvation ketosis, alcoholic ketoacidosis, and toxic alcohol ingestions.

What is the anion gap and how is it calculated?

Anion gap = Sodium - (Chloride + Bicarbonate). Normal range is 8-12 mEq/L. An elevated anion gap indicates metabolic acidosis from conditions like diabetic ketoacidosis, lactic acidosis, renal failure, or toxic ingestions (MUDPILES mnemonic). A normal anion gap acidosis suggests GI or renal bicarbonate loss.

How do I interpret the result?

Results are displayed with a label and unit to help you understand the output. Many calculators include a short explanation or classification below the result (for example, a BMI category or risk level). Refer to the worked examples section on this page for real-world context.

Can I share or bookmark my calculation?

You can bookmark the calculator page in your browser. Many calculators also display a shareable result summary you can copy. The page URL stays the same so returning to it will bring you back to the same tool.

How do I get the most accurate result?

Enter values as precisely as possible using the correct units for each field. Check that you have selected the right unit (e.g. kilograms vs pounds, meters vs feet) before calculating. Rounding inputs early can reduce output precision.