Anion Gap Calculator Formula
Understand the math behind the anion gap calculator. Each variable explained with a worked example.
Formulas Used
Anion Gap
anion_gap_val = sodium - chloride - bicarbonateAlbumin-Corrected AG
corrected_ag = (sodium - chloride - bicarbonate) + 2.5 * (4.0 - albumin)Delta Ratio (if AG elevated)
delta_delta = (sodium - chloride - bicarbonate - 12) / (24 - bicarbonate)Variables
| Variable | Description | Default |
|---|---|---|
sodium | Sodium (Na+)(mEq/L) | 140 |
chloride | Chloride (Cl-)(mEq/L) | 104 |
bicarbonate | Bicarbonate (HCO3-)(mEq/L) | 24 |
albumin | Albumin(g/dL) | 4 |
How It Works
Anion Gap Formula
AG = Na+ - Cl- - HCO3-
Normal Range
Normal anion gap: 8-12 mEq/L (without potassium)
Albumin Correction
Corrected AG = AG + 2.5 x (4.0 - Albumin)
Low albumin can mask an elevated anion gap.
Common Causes of Elevated Anion Gap (MUDPILES)
Methanol, Uremia, Diabetic ketoacidosis, Propylene glycol, Iron/Isoniazid, Lactic acidosis, Ethylene glycol, Salicylates
Worked Example
Na 140, Cl 104, HCO3 24, Albumin 4.0.
- 01AG = 140 - 104 - 24 = 12 mEq/L
- 02Corrected AG = 12 + 2.5 x (4.0 - 4.0) = 12
- 03Normal anion gap (8-12)
Frequently Asked Questions
What is the anion gap?
The anion gap represents the difference between measured cations and anions in the blood. It helps identify the cause of metabolic acidosis.
What causes a high anion gap?
Common causes include diabetic ketoacidosis (DKA), lactic acidosis, kidney failure, and toxic ingestions like methanol or ethylene glycol.
Why correct for albumin?
Albumin is a negatively charged protein. Low albumin levels reduce the anion gap, potentially masking an acidosis. The correction adds 2.5 for each g/dL albumin is below 4.0.
Ready to run the numbers?
Open Anion Gap Calculator