Anion Gap Calculator
Calculate the serum anion gap from sodium, chloride and bicarbonate, with an optional albumin-corrected value. Example: sodium 140, chloride 104, bicarbonate 24 gives an anion gap of 12 mEq/L.
Show steps
How to use the Anion Gap Calculator
- Enter the values in the fields.
- Press Calculate to see the result with the steps shown.
Formula and method
Anion gap = Na – (Cl + HCO3). Albumin-corrected gap = anion gap + 2.5 x (4.0 – albumin in g/dL).
Reading the anion gap
| Anion gap | Meaning |
|---|---|
| Below 3 | Unusually low; check labs, albumin, paraproteins |
| 3 to 12 | Normal |
| 13 to 20 | Mildly raised |
| Above 20 | Strongly suggests a gap acidosis |
Causes of a high anion gap (MUDPILES)
| Letter | Cause |
|---|---|
| M | Methanol |
| U | Uremia |
| D | Diabetic and other ketoacidosis |
| P | Paraldehyde, propylene glycol |
| I | Isoniazid, iron |
| L | Lactic acidosis |
| E | Ethylene glycol |
| S | Salicylates |
Why correct for albumin
Albumin is the main unmeasured anion. When it is low the gap falls, so a seemingly normal gap can hide a real acidosis. This calculator is for education and is not medical advice. Lab and clinical decisions belong with a qualified clinician who sees the whole picture.
Whether potassium is included
Some labs include potassium, which adds roughly 4 mEq/L to the normal range. This calculator uses the common form without potassium.
Frequently asked questions
What is a normal anion gap?
About 3 to 12 mEq/L without potassium.
What causes a high anion gap?
Ketoacidosis, lactic acidosis, kidney failure and some poisonings.
What does a low anion gap mean?
Often low albumin, lab error or rarely paraproteins.
Do I include potassium?
Usually no; follow your lab.
Why correct for albumin?
Because low albumin lowers the gap.
Is this diagnostic?
No, it is a screening clue.
Sources
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