Enter your sodium, chloride, bicarbonate, and CO2 levels into the calculator to determine your anion gap.

Anion Gap Calculation Formula

The following formula is used to calculate the anion gap from your electrolyte levels.

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

Variables:

  • Na+ is the sodium concentration (mEq/L)
  • Cl– is the chloride concentration (mEq/L)
  • HCO3– is the bicarbonate concentration (mEq/L)

To calculate the anion gap, subtract the sum of chloride and bicarbonate concentrations from the sodium concentration.

What is Anion Gap Calculation?

Anion gap calculation is a crucial diagnostic tool used to identify the causes of metabolic ac idosis. The anion gap measures the difference between primary measured cations (sodium) and the primary measured anions (chloride and bicarbonate) in serum. A high anion gap indicates the presence of unmeasured anions in the blood, often suggesting conditions such as lactic acidosis, ketoacidosis, or ingestion of toxins. Conversely, a normal anion gap suggests hyperchloremic acidosis or non-anion gap metabolic acidosis, which can be due to gastrointestinal bicarbonate loss or renal tubular acidosis.

How to Calculate Anion Gap with CO2?

The following steps outline how to calculate the anion gap using CO2 levels along with other electrolytes.

  1. First, determine your sodium, chloride, bicarbonate, and CO2 levels.
  2. Use the modified formula: Anion Gap = Na+ – (Cl– + HCO3– + CO2).
  3. Calculate the anion gap by plugging in the values.
  4. Compare your result with normal reference ranges to understand any deviations.
  5. Consult with a healthcare professional to interpret the results accurately.

Example Problem:

Use the following variables as an example problem to test your knowledge.

Sodium (Na+) = 140 mEq/L

Chloride (Cl–) = 100 mEq/L

Bicarbonate (HCO3–) = 24 mEq/L

CO2 = 5 mEq/L

Anion Gap = 140 – (100 + 24 + 5) = 11 mEq/L

FAQ

1. What is the normal range for anion gap?

The normal range for anion gap is typically 8-16 mEq/L, though this can vary slightly based on the laboratory standards.

2. How is the anion gap used in clinical practice?

The anion gap is used to identify the cause of metabolic acidosis. A high anion gap suggests the presence of unmeasured anions, whereas a normal anion gap suggests a hyperchloremic acidosis.

3. Can anion gap be used to monitor treatment?

Yes, the anion gap can be used to monitor the effectiveness of treatment for conditions like diabetic ketoacidosis or lactic acidosis.

4. Is the anion gap affected by albumin levels?

Yes, hypoalbuminemia can lower the anion gap, so albumin levels should be considered when interpreting the anion gap.

5. Are there other causes of high anion gap besides acidosis?

Yes, other causes can include renal failure, ingestion of toxins (e.g., methanol, ethylene glycol), and certain medications.