Serum Anion Gap CalculatorFree online fitness & health calculator — instant results, no sign-up
Calculate the serum anion gap without potassium.
For general information only. This is not medical advice, diagnosis, dosing guidance or a treatment recommendation. Talk to a doctor or other qualified health professional about your health, pregnancy, or diet.
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About the Serum Anion Gap Calculator
The Serum Anion Gap Calculator estimates the adult serum anion gap from sodium, chloride, and bicarbonate concentrations, without including potassium. This calculated difference helps clinicians assess acid–base disturbances, but it cannot establish a diagnosis by itself.
- Sodium (mmol/L)
- The sodium concentration in your blood sample, entered in mmol/L, with a default value of 140.
- Chloride (mmol/L)
- The chloride concentration in your blood sample, entered in mmol/L, with a default value of 104.
- Bicarbonate (mmol/L)
- The bicarbonate concentration in your blood sample, entered in mmol/L, with a default value of 24.
Formula and method
AG = Na⁺ − (Cl⁻ + HCO₃⁻); with the default inputs: AG = 140 − (104 + 24) = 12 mmol/L.
- AGSerum anion gap without potassium, in mmol/L.
- Na⁺Serum sodium concentration, in mmol/L.
- Cl⁻Serum chloride concentration, in mmol/L.
- HCO₃⁻Serum bicarbonate concentration, in mmol/L.
The calculator adds chloride and bicarbonate, then subtracts their sum from sodium. It does not include potassium or adjust for albumin. With the default inputs, chloride plus bicarbonate is 104 + 24 = 128 mmol/L, and the anion gap is 140 − 128 = 12 mmol/L.
Worked example
These are the calculator's starting values and the results it actually produces for them.
Inputs
- Sodium140 mmol/L
- Chloride104 mmol/L
- Bicarbonate24 mmol/L
Results
- Anion gap (without potassium)12 mmol/L
- NoteEducational estimate for adults; not a diagnosis or treatment recommendation.
How to use the Serum Anion Gap Calculator
- 1Find sodium, chloride, and bicarbonate results from the same blood sample and confirm that they are reported in mmol/L.
- 2Enter sodium in the Sodium (mmol/L) field; the default is 140.
- 3Enter chloride in the Chloride (mmol/L) field; the default is 104.
- 4Enter bicarbonate in the Bicarbonate (mmol/L) field; the default is 24.
- 5Read the calculated anion gap and educational note, and compare the result with your laboratory’s reference interval for an anion gap calculated without potassium.
Reading your result
The “Anion gap (without potassium)” row reports the calculated difference in mmol/L; the default inputs produce 12 mmol/L. Whether this falls within the expected range depends on the laboratory’s method and reference interval. An elevated gap can suggest increased unmeasured anions, but interpretation requires other findings, including bicarbonate, albumin, and clinical context. The “Note” row states: “Educational estimate for adults; not a diagnosis or treatment recommendation.”
Limitations
This tool assumes accurate electrolyte measurements from the same blood sample and consistent units. It does not correct for albumin; low albumin can lower the measured anion gap and obscure an elevation. Reference intervals vary by laboratory, and ranges for formulas that include potassium are not interchangeable with this result. The calculator does not assess pH, identify the cause of an abnormal gap, or exclude an acid–base disorder when the gap is within the laboratory’s reference interval. It is an educational tool for adults, not a guide to changing diet, supplements, or treatment.
Common questions
Why does this serum anion gap calculator leave out potassium?+
This tool uses the common formula sodium minus chloride plus bicarbonate: AG = Na⁺ − (Cl⁻ + HCO₃⁻). Some laboratories include potassium, which produces a higher calculated value and requires a different reference interval.
Is the default result of 12 mmol/L normal?+
A result of 12 mmol/L falls within some commonly used reference intervals, but it is not universally normal. Use your laboratory’s interval for an anion gap without potassium and consider albumin and other clinical findings.
Can I use the total CO₂ result on my chemistry panel for bicarbonate?+
Serum total CO₂ on a routine chemistry panel mainly represents bicarbonate and is commonly used for this calculation. Confirm that the result is serum total CO₂ in mmol/L, not the partial pressure of CO₂ from a blood gas.
Does a normal anion gap rule out metabolic acidosis?+
No. Metabolic acidosis can occur with a normal anion gap, and low albumin can mask an increased gap. Assessment requires bicarbonate and other clinical information, sometimes including blood gas measurements.
Does the calculator save my information?+
Calculations run in your browser. While signed in, inputs and results are automatically recorded in account history; saving a result creates a separate saved record.
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Results are estimates for informational purposes and are not financial, medical or legal advice.