Anion Gap Calculator
Calculate the serum anion gap to help diagnose and evaluate metabolic acidosis. This calculator includes optional albumin correction for more accurate assessment in patients with low albumin levels. The anion gap helps identify the cause of acid-base disturbances and is essential for diagnosing high anion gap metabolic acidosis (MUDPILES).
Normal range: 135-145 mEq/L
Normal range: 96-106 mEq/L
Normal range: 22-28 mEq/L
Normal range: 3.5-5.5 g/dL
What is anion gap and why is it important?
Anion gap is a calculated value that represents the difference between measured cations (sodium) and measured anions (chloride and bicarbonate) in the blood. It helps diagnose and evaluate metabolic acidosis, identifying the cause of acid-base disturbances. A normal anion gap is typically 8-16 mEq/L (or 3-11 mEq/L when corrected for albumin).
How is anion gap calculated?
The standard formula is: Anion Gap = Na+ - (Cl- + HCO3-). Some formulas include potassium: (Na+ + K+) - (Cl- + HCO3-), but this is less common. The result represents unmeasured anions in the blood, such as proteins, phosphates, sulfates, and organic acids.
What does a high anion gap indicate?
A high anion gap (>16 mEq/L) indicates metabolic acidosis and can be caused by: lactic acidosis, ketoacidosis (diabetic, alcoholic, or starvation), renal failure, toxins (methanol, ethylene glycol, aspirin), or severe dehydration. The mnemonic MUDPILES helps remember causes: Methanol, Uremia, Diabetic ketoacidosis, Paraldehyde/Propylene glycol, Isoniazid/Iron, Lactic acidosis, Ethylene glycol, Salicylates.
Why correct anion gap for albumin?
Albumin is a major unmeasured anion. Low albumin levels can falsely lower the anion gap, potentially masking metabolic acidosis. For every 1 g/dL decrease in albumin below 4 g/dL, the anion gap decreases by approximately 2.5 mEq/L. Correcting for albumin provides a more accurate assessment, especially in patients with hypoalbuminemia.