Anion Gap Calculator

How it is calculated

The tool subtracts the two main measured anions from the main measured cation: AG = Na − (Cl + HCO₃). Na is serum sodium, Cl is serum chloride and HCO₃ is serum bicarbonate, all in mEq/L (the same numeric value as mmol/L for these monovalent ions). Potassium is not included. The result is rounded to one decimal and labelled Low if below 8, Normal from 8 to 12 inclusive, and High above 12. Labs use different analysers and reference ranges, so treat these cut-offs as a rule of thumb and compare against your own laboratory's range.

Common mistakes

• Adding potassium to the formula. This tool uses the version without K⁺; mixing versions shifts the result by about 4 and changes the reference range.
• Entering bicarbonate from a blood gas and chloride from a different draw or time point; the three values should come from the same sample.
• Mixing units, for example entering sodium in mg/dL. All three fields expect mEq/L (mmol/L).
• Ignoring low albumin. Low albumin lowers the true gap, so a result that looks normal can hide a real elevation.
• Treating the label as a diagnosis. It only classifies the number; interpretation depends on the clinical picture.