Anion Gap Calculator
What is Anion Gap Calculator
The anion gap calculator works out the difference between measured cations and anions in the blood, a quick screen for high anion gap metabolic acidosis. It uses Na minus the sum of chloride and bicarbonate, optionally adding potassium, and can correct the result for a low albumin, which otherwise hides a real acidosis. Values come out in mmol/L, the same as mEq/L for these ions.
How to use
- Enter sodium, chloride and bicarbonate in mmol/L.
- Add potassium if your lab reports the gap with it included.
- Enter albumin in g/dL to see the albumin-corrected gap.
- Read the anion gap and whether it sits low, normal or high.
When to use it
Reviewing a metabolic panel and want to know if there is a hidden acidosis? Enter sodium 140, chloride 100 and bicarbonate 10 and you get a gap of 30 mmol/L, clearly high and pointing to a high anion gap acidosis. Add an albumin of 2.0 g/dL and the corrected gap climbs further, which matters because a low albumin can mask an elevated gap on the raw numbers.
Frequently asked questions
What is a normal anion gap?
Without potassium a normal gap is roughly 3 to 11 mmol/L; when potassium is included it is about 7 to 16. Reference ranges vary slightly between labs because they depend on how chloride is measured.
Why correct for albumin?
Albumin is the main unmeasured anion, so a low albumin lowers the measured gap. For every 1 g/dL that albumin falls below 4.0, add about 2.5 to the gap, otherwise a real high anion gap acidosis can look normal.
Should I include potassium?
Both forms are valid. Including potassium raises the gap by the potassium value and shifts the reference range up. Use whichever convention your lab or protocol reports so your result matches the expected range.
Can I share this tool with my inputs pre-filled?
Yes. The URL updates automatically as you type. Copy it from the address bar or use the Copy link button, and anyone who opens the link will see your exact inputs ready to go.
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