Anion Gap Calculator Formula

Understand the math behind the anion gap calculator. Each variable explained with a worked example.

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Formulas Used

Anion Gap

anion_gap_val = sodium - chloride - bicarbonate

Albumin-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

VariableDescriptionDefault
sodiumSodium (Na+)(mEq/L)140
chlorideChloride (Cl-)(mEq/L)104
bicarbonateBicarbonate (HCO3-)(mEq/L)24
albuminAlbumin(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.

sodium = 140chloride = 104bicarbonate = 24albumin = 4
  1. 01AG = 140 - 104 - 24 = 12 mEq/L
  2. 02Corrected AG = 12 + 2.5 x (4.0 - 4.0) = 12
  3. 03Normal anion gap (8-12)

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