Anion Gap Calculator

How to calculate Anion Gap calculator?

The anion gap estimates unmeasured serum anions and helps identify causes of metabolic acidosis.

Key formula: Anion Gap (AG) = [Na+] - ([Cl-] + [HCO3-]). For low albumin, correct using cAG = AG + 2.5 × (4.0 - albumin[g/dL]).

Using the Anion Gap calculator calculator: an example

Example input: Na+ 140 mEq/L, Cl- 100 mEq/L, HCO3- 24 mEq/L, albumin 3.0 g/dL.

Step-by-step calculation:

1. Calculate AG: AG = 140 - (100 + 24) = 16 mEq/L.
2. Calculate corrected AG for albumin 3.0 g/dL: cAG = 16 + 2.5 × (4.0 - 3.0) = 18.5 mEq/L.
3. Compare to typical normal range (≈8–12 mEq/L); values above this suggest excess unmeasured anions.
4. Interpret in clinical context and review other labs and patient history before concluding cause.

Frequently Asked Questions

What is a normal anion gap?

A typical reference range is about 8–12 mEq/L, but exact limits vary by laboratory and measurement method.

When should I use the corrected anion gap?

Use the corrected anion gap when albumin is below normal, as hypoalbuminemia lowers the measured AG and may mask an elevated gap.

Can medications or toxins change the anion gap?

Yes. Substances such as salicylates, methanol, ethylene glycol and some drugs can raise the anion gap by adding unmeasured anions.

Does an elevated anion gap always indicate metabolic acidosis?

An elevated AG suggests accumulation of unmeasured anions but should be interpreted with pH, bicarbonate and clinical context to confirm metabolic acidosis.