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Anion Gap Calculator

Compute the serum anion gap with optional potassium and albumin correction. Includes delta-gap analysis for mixed acid-base disorders.

Serum anion gap

mEq/L
mEq/L
mEq/L
g/dL

Anion gap

12 mEq/L

normal

AG = Na - (Cl + HCO3)

Medical disclaimer

This tool is for educational use only. The anion gap is one piece of an acid-base workup and never replaces clinical judgment, arterial blood gas analysis, or treatment by a qualified clinician. Reference ranges vary by lab and by whether potassium is included.

Anion Gap Reference Ranges

The selected formula is sodium minus chloride and bicarbonate, with potassium added only when requested.

InterpretationWithout potassiumWith potassiumFormula
LowBelow 8 mEq/LBelow 12 mEq/LNa − (Cl + HCO₃)
Normal8-12 mEq/L12-16 mEq/LSelected convention
ElevatedAbove 12 to 16 mEq/LAbove 16 to 20 mEq/LSelected convention
HighAbove 16 mEq/LAbove 20 mEq/LSelected convention

Anion gap patterns require the full laboratory and clinical picture. Do not use this table to self-diagnose metabolic acidosis.

Frequently Asked Questions about the Anion Gap Calculator

What is the anion gap?
The anion gap (AG) is the difference between measured cations (sodium, optionally potassium) and measured anions (chloride and bicarbonate). It estimates the unmeasured anions (mostly albumin, phosphate, sulfate, and organic acids like lactate and ketoacids) in plasma.
What is a normal anion gap?
Most labs report 8 to 12 mEq/L for the standard formula (without potassium). Values above 12 suggest a high-AG metabolic acidosis; values below 8 are uncommon and can point to hypoalbuminemia or paraproteinemias.
What are the MUDPILES causes of a high anion gap?
MUDPILES is a mnemonic for the major causes of high-anion-gap metabolic acidosis: Methanol, Uremia, Diabetic ketoacidosis, Propylene glycol (or Paraldehyde), Iron or Isoniazid, Lactic acidosis, Ethylene glycol, Salicylates. The calculator flags AG above 16 as suggestive.
Why correct the anion gap for albumin?
Albumin contributes most of the unmeasured anion charge. A low albumin (common in critically ill or chronically ill patients) lowers the measured AG by about 2.5 mEq/L for every 1 g/dL drop, which can mask a real high-gap acidosis. The albumin-corrected AG adjusts back to a normal albumin of 4.0 g/dL.
Is this a medical diagnosis tool?
No. Educational only. Real acid-base interpretation requires an arterial blood gas, the clinical context, and physician judgment. Do not change patient care based on this calculator.

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