This anion gap calculator allows you to compute the AG value and delta gap for the sodium, chloride and bicarbonate values you input in the Na Cl and HCO3 fields. You can discover more on the implications of the anion gap below the form.

Sodium (Na):*
Chloride (Cl):*
Bicarbonate (HCO3-):*
Sodium (Na):*
Chloride (Cl):*
Bicarbonate (HCO3-):*

How does this anion gap calculator work?

This is a health tool that can prove useful when analyzing the result of certain medical tests. It helps anyone quickly calculate the anion gap in mEq/L based on the Na (Sodium), Cl (Chloride) and HCO3 (Bicarbonate) values. The first two should be no lower than 80mEq/L for Na and 60mEq/L for Cl. The reference range for AG is 3-11 mEq/L.

This anion gap calculator is based on the following formulas that allow to identify the cause of metabolic acidosis:

- Anion gap (mEq/L) = [Na] – ([Cl] + [HCO3])

- Delta gap (mEq/L) = Anion Gap – Baseline gap (here 12)

- Delta ratio = Delta gap / (24 – [HCO3])

The two measurement units supported are:

- milliequivalents/liter abbreviated as mEq/L;

- millimole/liter abbreviated as mmol/L.

Example calculation

Let’s take into account that we are presented with the following data:

Na = 145 mEq/L; Cl = 104 mEq/L; HCO3 = 26 mEq/L

Anion gap = 145 – (104 +26) => AG = 15 mEq/L

Delta gap = 15 - 12 = 3

Delta ratio = 3 / (24 – 26) => Delta ratio = -1.5 

About the anion gap

This is an indicator allowing us to give measure to the undetermined ions in plasma or serum. Anion gap is basically the difference between primary measured cations and anions in serum. What results is the unmeasured concentration of anions in the plasma. Then the result is then defined as low, normal or high.

While the serum anion gap complete formula is (Na + K) - (Cl + HCO3), the simpler version, presented above, which excludes K is commonly used.

Electrolytes serum range
Sodium 135-145 mEq/L
Chloride 95-105 mEq/L
Bicarbonate 22-28 mEq/L
Potassium 3.5-5.0 mEq/L

Clinical uses of the anion gap

- Representative for the presence of metabolic acidosis

- Differentiation between the causes of metabolic acidosis

- Severity assessment of the acidosis

- Monitoring the response to treatment

A low result, under 6 mEq/L is suggestive for hypoalbuminemia, albumin being the most relevant unmeasured anion. A normal value in the range of 3 to 11 mEq/L but accompanied by other symptoms may suggest a loss of bicarbonate, recovery from diabetic ketoacidosis or renal tubular acidosis. High levels, above 11mEq/L suggest uremia, diabetic ketoacidosis, lactic acidosis or renal failure.

About the delta gap and ratio

This is a concept related to the anion gap and is defined as the increase in AG (delta gap) divided by the decrease in bicarbonate (delta ratio). Low ratios occur when the HCl levels and although the rise in plasma of chloride is not seen in the anion gap, it is accompanied by the decrease in bicarbonate. High levels occur when there are elevated bicarbonate values, often at the onset of metabolic acidosis.

Delta ratio Guidelines
< 0.4 Hyperchloraemic acidosis with normal anion gap
0.4 - 0.8 High or normal anion gap acidosis
1 - 2 Lactic acidosis; Diabetic ketoacidosis
>2 Signals elevated HCO3 levels associated with metabolic alkalosis or compensated respiratory acidosis


1) Gabow PA, Kaehny WD, Fennessey PV, Goodman SI, Gross PA, Schrier RW. (1980) Diagnostic importance of an increased serum anion gap. N Engl J Med; 303(15):854-8.

2) Oh MS, Carroll HJ. (1977) The anion gap. N Engl J Med; 297(15):814-7.

19 May, 2015