Anion Gap & Delta Ratio Calculator
The anion gap differentiates causes of metabolic acidosis. The standard formula is sodium minus the sum of chloride and bicarbonate; normal values fall around 8–12 mmol/L. Hypoalbuminaemia lowers the apparent gap, so an albumin-corrected gap (adds 2.5 per 1 g/dL below 4) is recommended when albumin is reduced. The delta ratio compares the rise in anion gap to the fall in bicarbonate to detect mixed acid-base disorders. This calculator returns the uncorrected gap, the albumin-corrected gap, the delta ratio, and a differential framework consistent with the Kraut & Madias review in Nature Reviews Nephrology.
This tool is for educational and decision-support use only. It does not replace independent clinical judgement. Always verify against the current guideline, FDA label, or specialty reference cited below before acting. Do not enter patient identifiers (name, MRN, dates of service).
Tool
Who this is for
- Internal medicine residents on inpatient services
- Critical care and emergency medicine clinicians
- Toxicology and nephrology consultations
How to interpret the result
| Score / band | Interpretation |
|---|---|
| AG ≤ 12 | Normal — investigate non-AG metabolic acidosis (RTA, GI losses) if HCO₃⁻ low. |
| AG 13–20 | Elevated — common differentials include lactate, DKA, uraemia, toxic ingestions. |
| AG > 20 | Markedly elevated — urgent toxic / metabolic workup commonly considered. |
| Delta ratio < 1 | Mixed AG and non-AG metabolic acidosis. |
| Delta ratio 1–2 | Pure high-AG metabolic acidosis. |
| Delta ratio > 2 | Pre-existing metabolic alkalosis or chronic respiratory acidosis. |