Q&A for How to Calculate Anion Gap

The anion gap is the difference between primary measured cations (sodium Na+ and potassium K+) and the primary measured anions (chloride Cl- and bicarbonate HCO3-) in serum. If the urine anion gap is zero or negative but the serum AG is positive, the source is most likely gastrointestinal (diarrhea or vomiting).

If your results show a low anion gap, it may mean you have a low level of albumin, a protein in the blood. Low albumin may indicate kidney problems, heart disease, or some types of cancer. Since low anion gap results are uncommon, retesting is often done to ensure the results are accurate.

You can't calculate the anion gap without bicarbonate (HCO3) levels. The formula for anion gap is AG = (Na + K) - (Cl + HCO3). Since you're missing HCO3, you won't get an accurate result. Anion gap helps in diagnosing certain conditions like metabolic acidosis. If you're missing a lab value, it's best to get it before making calculations for accurate diagnosis.

The anion gap is a calculated value derived from the concentrations of certain electrolytes in the blood, typically sodium (Na+), chloride (Cl-), and bicarbonate (HCO3-). It is used to help identify the cause of metabolic acidosis and other conditions. A normal anion gap ranges from 8 to 12 mEq/L, though this can vary slightly depending on the laboratory. If your anion gap is above normal and increases with each test, that suggests an accumulation of unmeasured anions in the blood.

To calculate the anion gap, use the formula: Anion Gap = Na⁺ - (Cl⁻ + HCO₃⁻). For example, with Sodium (Na⁺) = 140 mEq/L, Chloride (Cl⁻) = 100 mEq/L, and Bicarbonate (HCO₃⁻) = 24 mEq/L, the calculation is Anion Gap = 140 - (100 + 24) = 16 mEq/L. This value is slightly above the normal range of 8 to 12 mEq/L, which can vary depending on the lab.

You can calculate the anion gap from a CMP using the electrolytes sodium, chloride, and bicarbonate. A blood gas test is not necessary for this calculation.