Anion Gap Calculator

Anion Gap Calculator for Nephrology. A high gap suggests additional unmeasured anions; it does not by itself establish acidemia or identify the cause. Albumin adjustment is an approximation, not a measurement of a 'true' gap.

For shared guidance on choosing a tool and documenting results, read the clinical calculator workflow.

How this calculator works

The potassium-excluding anion gap is sodium minus chloride minus bicarbonate, using matching electrolyte units. Optional albumin adjustment adds approximately 2.5 x (4 - albumin in g/dL).

When to use this calculator

To organize an acid-base assessment alongside pH, bicarbonate, lactate, ketones and clinical context. Compare with the reporting laboratory's reference interval.

Inputs used

  • Sodium
  • Chloride
  • Bicarbonate
  • Albumin when correcting the gap

Clinical interpretation

A high gap suggests additional unmeasured anions; it does not by itself establish acidemia or identify the cause. Albumin adjustment is an approximation, not a measurement of a 'true' gap.

Worked example

Sodium 140, chloride 100 and bicarbonate 12 give an anion gap of 28 mEq/L. With albumin 2 g/dL, the adjusted estimate is 28 + 2.5 x 2 = 33.

Limitations and safety notes

Laboratory methods and baseline albumin affect interpretation. The 2024 hyperglycemic-crisis consensus does not recommend anion gap as the preferred measure of DKA resolution.

Frequently asked questions

Does a normal gap exclude all metabolic acidosis?

No. Bicarbonate loss and other processes can produce metabolic acidosis without an elevated gap.

Can I use the adjusted gap to stop DKA treatment?

Not on its own. Follow the appropriate ketone and acid-base resolution criteria.

References

  • Figge J et al. Anion gap and hypoalbuminemia. 1998. PMID: 9824071. https://pubmed.ncbi.nlm.nih.gov/9824071/
  • Hyperglycemic Crises in Adults With Diabetes: A Consensus Report. Diabetes Care. 2024. https://diabetesjournals.org/care/article/47/8/1257/156808/Hyperglycemic-Crises-in-Adults-With-Diabetes-A

Editorial review and citation methodology

Maintained by the Quick Medical Calculator Editorial Team. Content record date: September 7, 2026. A content date is not evidence of independent clinical review. Individual clinical sign-off is not recorded on this page.

  • Prefer original validation studies for scoring systems and prediction tools.
  • Use current specialty society guidance, transplant allocation policy, public health guidance, or regulator resources when they govern clinical use.
  • Include limitations and safety notes when a calculator is population-specific, context-dependent, or unsuitable as a standalone decision tool.

Related reviewed calculators