Corrected Anion Gap Calculator

Corrected AG = AG + 2.5 × (4.0 − Albumin)

Low albumin hides a high anion gap. This calculator adjusts for albumin to reveal the true anion gap. Enter your lab values below for instant results with clinical interpretation.

Calculate Now ↓ Learn More
Interactive Tool

Calculate Your Corrected Anion Gap

Enter electrolyte values and albumin to get the albumin-corrected anion gap with clinical interpretation.

Lab Values

All electrolytes in mEq/L, Albumin in g/dL

Results

Enter values and click Calculate to see your results

Formula & Calculation

Corrected Anion Gap Formula

How to adjust the anion gap when albumin is low.

Standard Correction

Corrected AG = AG + 2.5 × (4.0 − Albumin)

For every 1 g/dL drop in albumin below the normal of 4 g/dL, add 2.5 mEq/L to the calculated anion gap. This accounts for the lost negative charge that albumin normally contributes.

Why 2.5?

Each 1 g/dL albumin ≈ 2.5 mEq/L charge

At physiological pH, each gram of albumin carries about 2.5 mEq of negative charge. When albumin drops, those charges disappear from the unmeasured anion pool, and the baseline anion gap falls. The correction adds them back.

Step-by-Step Calculation

1
Calculate the standard anion gap. AG = Na⁺ − (Cl⁻ + HCO₃⁻). For example: 140 − (104 + 24) = 12 mEq/L.
2
Check the albumin level. Normal albumin is about 4.0 g/dL. If the patient's albumin is 2.0 g/dL, the deficit is 2.0 g/dL.
3
Apply the correction. Multiply the deficit by 2.5: 2.5 × (4.0 − 2.0) = 5.0 mEq/L.
4
Add to the AG. Corrected AG = 12 + 5.0 = 17 mEq/L. This patient actually has a high anion gap that the standard formula missed.

Live Calculation Preview

Updates in real-time as you change values in the calculator above.

Understanding the Basics

What is the Corrected Anion Gap?

Why albumin matters for anion gap interpretation.

Definition

The corrected anion gap adjusts the standard anion gap for the patient's albumin level. Albumin is the largest contributor to the unmeasured anion pool. When albumin is low, the baseline anion gap drops — a patient with hypoalbuminemia can have a "normal" anion gap despite having significant metabolic acidosis.

Clinical Importance

Critically ill patients, cirrhotics, and those with nephrotic syndrome often have low albumin. Without correction, you might miss a high anion gap acidosis entirely. Studies show that up to 50% of elevated anion gaps are missed in patients with albumin below 2.5 g/dL when the correction isn't applied.

Uncorrected AG
Albumin Correction
Corrected AG
Reference Values

Corrected Anion Gap Normal Range

Same reference range as standard AG — the correction brings values back to a normal-albumin baseline.

ParameterNormal RangeUnitNotes
Albumin3.5 – 5.0g/dLMain unmeasured anion
Standard AG8 – 12mEq/LNa⁺ − (Cl⁻ + HCO₃⁻)
Corrected AG8 – 12mEq/LAfter albumin adjustment
Correction Factor2.5 per 1 g/dLmEq/L per g/dLAdded for each g/dL below 4.0

Where Does Your Corrected AG Fall?

This gauge shows your corrected anion gap. Change values above to see the needle move.

Clinical Interpretation

Corrected Anion Gap Interpretation

What different corrected anion gap values mean after albumin adjustment.

🔴

High Corrected AG

Corrected AG > 12 mEq/L
  • True high AG acidosis unmasked by correction
  • DKA in a malnourished patient
  • Lactic acidosis in sepsis with low albumin
  • Toxic ingestion in cirrhotics
  • Uremic acidosis in nephrotic syndrome
🟢

Normal Corrected AG

Corrected AG 8–12 mEq/L
  • True normal — no hidden gap acidosis
  • If acidosis present, consider non-AG causes
  • Diarrhea or RTA in hypoalbuminemic patient
  • Saline overload
  • Confirms low AG was purely from low albumin
🔵

Low Corrected AG

Corrected AG < 8 mEq/L
  • Rare after correction
  • Consider lab error
  • Multiple myeloma (cationic IgG)
  • Lithium toxicity
  • Severe hypercalcemia or hypermagnesemia
When to Use

When to Correct the Anion Gap

Clinical scenarios where albumin correction changes management.

Key Indications

  • ICU patients — Most critically ill patients have low albumin. Always correct the AG in the ICU.
  • Liver disease — Cirrhotics have chronically low albumin and are at risk for lactic acidosis and toxin exposure.
  • Nephrotic syndrome — Massive albumin loss through the kidneys lowers the baseline AG significantly.
  • Malnutrition — Elderly and malnourished patients may have albumin below 2.5 g/dL.
  • Sepsis workup — Don't miss lactic acidosis because albumin is low.
  • Any "borderline normal" AG — If the standard AG is 10–12 in a hypoalbuminemic patient, correct it to check for a hidden elevation.
Common Questions

Frequently Asked Questions

Answers to common questions about the corrected anion gap.

Albumin is the main unmeasured anion in the blood. It carries a negative charge at physiological pH. When albumin drops, the total unmeasured anions decrease, and the anion gap falls with them. A patient with low albumin might have a "normal" AG of 10 — but after correction, the true AG could be 15 or higher, revealing a hidden metabolic acidosis.
Corrected AG = Calculated AG + 2.5 × (4.0 − measured albumin). First calculate the standard AG (Na⁺ − Cl⁻ − HCO₃⁻), then add 2.5 mEq/L for every 1 g/dL that albumin is below 4.0 g/dL. If albumin is 2.0 g/dL, you add 2.5 × 2 = 5.0 mEq/L.
Use it whenever the patient's albumin is below 4.0 g/dL. This is especially important in ICU patients, cirrhotics, patients with nephrotic syndrome, the elderly, and anyone with malnutrition. In these populations, the standard AG alone can miss up to half of all elevated AG acidoses.
The normal corrected anion gap is 8–12 mEq/L — the same as the standard AG. The correction is designed to bring the value back to what it would be if albumin were normal (4.0 g/dL). Values above 12 after correction suggest a true high anion gap metabolic acidosis.
Yes, the formula works in both directions. If albumin is above 4.0 g/dL (rare), the correction will subtract from the AG. But in practice, high albumin is uncommon, and the correction is almost always used to adjust upward for low albumin.
Yes. In fact, using the corrected AG in the delta-delta ratio gives a more accurate assessment of mixed acid-base disorders. Use the corrected AG instead of the standard AG: Delta Ratio = (Corrected AG − 12) / (24 − HCO₃⁻). This helps avoid misclassifying a mixed disorder in hypoalbuminemic patients.