Anion Gap Calculator

Calculate serum anion gap to help assess metabolic acidosis and other electrolyte disturbances.

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

Quick Reference

Normal Range
8-12 mEq/L
Without potassium
Formula
Na - (Cl + HCO3)
High AG Causes
MUDPILES
Methanol, Uremia, DKA...
Low AG
< 3 mEq/L
Hypoalbuminemia, myeloma

Results

Calculated
Anion Gap
0
mEq/L

Interpretation

Understanding Anion Gap

The anion gap (AG) is the difference between measured cations and anions in the blood. It represents unmeasured anions in the serum and is a valuable tool for diagnosing metabolic acidosis and identifying its underlying cause.

Anion Gap Formula

Anion Gap = Na+ - (Cl- + HCO3-)

Normal Range: 8-12 mEq/L

Some laboratories include potassium in the calculation, which yields a normal range of 10-20 mEq/L.

Albumin-Corrected Anion Gap

Albumin is a major unmeasured anion. In hypoalbuminemia, the AG may be falsely low:

Corrected AG = AG + 2.5 x (4.0 - albumin in g/dL)

Causes of High Anion Gap Metabolic Acidosis

Remember the mnemonic MUDPILES:

  • Methanol
  • Uremia (renal failure)
  • Diabetic ketoacidosis (DKA)
  • Propylene glycol
  • Isoniazid, Iron
  • Lactic acidosis
  • Ethylene glycol
  • Salicylates

Causes of Normal Anion Gap Metabolic Acidosis

Remember the mnemonic HARDUPS:

  • Hyperalimentation (TPN)
  • Acetazolamide, Addison's disease
  • Renal tubular acidosis
  • Diarrhea
  • Ureteral diversion
  • Pancreatic fistula
  • Saline infusion (dilutional)

Low Anion Gap

An AG less than 3 mEq/L may indicate:

  • Hypoalbuminemia
  • Multiple myeloma (paraproteinemia)
  • Lithium toxicity
  • Laboratory error

Delta-Delta Ratio

The delta-delta ratio helps identify mixed acid-base disorders:

Delta Ratio = (AG - 12) / (24 - HCO3-)

  • < 1: Mixed high AG and normal AG metabolic acidosis
  • 1-2: Pure high AG metabolic acidosis
  • > 2: High AG metabolic acidosis with metabolic alkalosis

Medical Disclaimer

This calculator is provided for educational and informational purposes only. It should not be used as a substitute for clinical judgment or professional medical advice. Interpretation of anion gap results requires consideration of the complete clinical picture, including patient history, physical examination, and other laboratory values. Always consult with a qualified healthcare provider for medical decisions.