# Anion Gap & Delta Ratio Calculator
> Free anion gap calculator with optional albumin correction and delta ratio. Based on Kraut & Madias (Nat Rev Nephrol 2012). Clinician decision support for metabolic-acidosis workup.

## Overview

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.

## 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 | Meaning |
|---|---|
| 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. |

## Cited source

**Kraut & Madias, Nat Rev Nephrol 2012** (2012) — Nature Reviews Nephrology

_Primary publication:_ Kraut JA, Madias NE. Nat Rev Nephrol 2012

## FAQs

### When is albumin correction needed?

Whenever albumin is below ~3.5 g/dL, the uncorrected anion gap underestimates the true gap. Critical illness frequently warrants the correction.

### What is the MUDPILES differential?

Methanol, uraemia, DKA, propylene glycol, isoniazid/iron, lactate, ethylene glycol, salicylates. GOLDMARK is a more modern variant.

### How is the delta ratio interpreted?

A delta ratio < 1 suggests a coexisting non-AG acidosis; 1–2 suggests pure high-AG acidosis; > 2 suggests an additional metabolic alkalosis or chronic respiratory acidosis.

### Does an osmolal gap add information?

Yes — when toxic ingestion is suspected, an elevated osmolal gap (measured − calculated osmolality > 10) supports methanol, ethylene glycol, propylene glycol, or alcohol toxicity.

### Can the anion gap be falsely normal?

Yes. Hypoalbuminaemia, lithium toxicity, multiple myeloma, and bromide intoxication can all narrow or distort the apparent gap.

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_Rounds AI is a citation-first clinical AI assistant. It supports clinical reasoning by surfacing cited information and is not a substitute for independent clinical judgement._