# Anion Gap Calculator

Calculate serum anion gap and albumin-corrected anion gap from lab values. Includes interpretation and delta-delta ratio for mixed acid-base disorders.

## What this calculates

The anion gap is a key lab value used to evaluate metabolic acidosis. Enter your sodium, chloride, and bicarbonate values to calculate the anion gap, and optionally add albumin for a corrected result.

## Inputs

- **Sodium (Na⁺)** (mEq/L) — min 100, max 180 — Normal range: 136-145 mEq/L
- **Chloride (Cl⁻)** (mEq/L) — min 70, max 130 — Normal range: 98-106 mEq/L
- **Bicarbonate (HCO₃⁻)** (mEq/L) — min 5, max 50 — Normal range: 22-28 mEq/L
- **Albumin (optional)** (g/dL) — min 0.5, max 7 — Normal: 3.5-5.0 g/dL. Enter to calculate corrected AG.

## Outputs

- **Anion Gap** — AG = Na⁺ - (Cl⁻ + HCO₃⁻)
- **Corrected Anion Gap** — formatted as text — Anion gap adjusted for albumin level
- **Interpretation** — formatted as text — Clinical interpretation of the anion gap
- **Delta-Delta (Δ/Δ)** — formatted as text — Delta ratio when AG is elevated (helps identify mixed disorders)

## Details

The anion gap is calculated as: **AG = Na+ - (Cl- + HCO3-)**. The normal range is 8-12 mEq/L. An elevated anion gap (above 12) suggests the presence of unmeasured anions, which points toward anion gap metabolic acidosis.

The classic mnemonic for elevated anion gap causes is MUDPILES: Methanol, Uremia, Diabetic ketoacidosis, Propylene glycol, Isoniazid/Iron, Lactic acidosis, Ethylene glycol, and Salicylates.

Albumin correction is important because albumin is a major unmeasured anion. Low albumin (common in hospitalized patients) artificially lowers the anion gap, potentially masking a true anion gap acidosis. The correction formula adds 2.5 mEq/L for every 1 g/dL that albumin is below 4.0. For example, if a patient has an AG of 10 but albumin of 2.0, the corrected AG is 10 + 2.5 x (4.0 - 2.0) = 15 mEq/L, revealing an elevated gap.

The delta-delta ratio helps identify mixed acid-base disorders when the AG is elevated. A ratio below 1 suggests an additional non-AG acidosis, 1-2 indicates a pure AGMA, and above 2 suggests a concurrent metabolic alkalosis.

**Disclaimer:** This calculator is for educational reference only. Always interpret lab values in the full clinical context. Do not use this tool as a substitute for professional medical judgment.

## Frequently Asked Questions

**Q: What is a normal anion gap?**

A: The traditional normal range is 8-12 mEq/L. Some labs use slightly different ranges (like 10-14) depending on their analyzers and whether potassium is included in the calculation. Always check your lab's specific reference range. An anion gap above 12 generally warrants investigation for anion gap metabolic acidosis.

**Q: Why correct the anion gap for albumin?**

A: Albumin carries a negative charge and is the largest unmeasured anion in the standard AG calculation. When albumin is low (very common in hospitalized, critically ill, or malnourished patients), the baseline anion gap drops. Without correction, you might miss a true anion gap acidosis. The rule of thumb: for every 1 g/dL drop in albumin below 4.0, the anion gap decreases by about 2.5 mEq/L.

**Q: What does a low anion gap mean?**

A: A low anion gap (below 8) is less common but can indicate hypoalbuminemia (the most frequent cause), lithium intoxication, multiple myeloma (where cationic paraproteins increase unmeasured cations), or laboratory error. If you see a low AG, check the albumin level first and calculate the corrected AG.

**Q: How do I use the delta-delta ratio?**

A: The delta-delta ratio compares the change in anion gap to the change in bicarbonate: (AG - 12) / (24 - HCO3). A ratio below 1 suggests the bicarbonate dropped more than the AG rose, meaning there is an additional non-anion-gap acidosis on top of the AGMA. A ratio above 2 means the AG rose more than bicarbonate dropped, suggesting a concurrent metabolic alkalosis is raising the bicarbonate. A ratio of 1-2 indicates a pure anion gap metabolic acidosis.

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Source: https://vastcalc.com/calculators/health/anion-gap
Category: Health & Fitness
Last updated: 2026-04-08