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Anion Gap Calculator

Calculate the serum anion gap to evaluate acid-base disorders.

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Formula

Anion Gap = Sodium - (Chloride + Bicarbonate)

Measures the difference between measured cations and anions in the blood.

Worked Example

Sodium 140, Chloride 104, Bicarbonate 24 -> Anion Gap 12.

Understanding the Anion Gap

The anion gap is a calculated value used to identify the cause of metabolic acidosis. It represents the "unmeasured anions" in the serum.
  • Standard formula: AG = Na+ - (Cl- + HCO3-)
  • Normal range is typically 8 to 12 mEq/L (if potassium is not included in the formula)
  • A "High Anion Gap Metabolic Acidosis" (HAGMA) suggests the presence of extra acids like lactate, ketones, or toxins (MUDPILES)
  • Low albumin can falsely lower the anion gap; for every 1 g/dL drop in albumin, the normal anion gap decreases by about 2.5 mEq/L

The anion gap is a diagnostic tool, not a diagnosis itself. It must be interpreted in the context of the patient's clinical presentation and other lab values.

You can also calculate changes using our Corrected Calcium Calculator or Creatinine Clearance Calculator.

Frequently Asked Questions

What is a normal anion gap range?

A common reference range is 8 to 12 mEq/L, though this can vary by laboratory and whether potassium is included in the calculation.

What does a high anion gap mean?

A high anion gap usually indicates metabolic acidosis caused by the addition of unmeasured acids, such as in diabetic ketoacidosis, lactic acidosis, or certain toxic ingestions.

Should I include potassium?

Most clinical practices use the formula without potassium. If you include it, the normal range shifts higher (typically 12 to 16 mEq/L).

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