About this calculator
The anion gap helps frame metabolic acidosis by estimating unmeasured anions. Albumin correction can be important when albumin is low.
Anion gap = Na − (Cl + HCO3), or Na + K − (Cl + HCO3) when potassium is included. Albumin correction = AG + 2.5 × (4 − albumin).
Source-mapped educational formula
Educational estimate only; not a diagnosis, prescription, or treatment plan.
Formula and method
AG = Na − (Cl + HCO3), optionally AG = Na + K − (Cl + HCO3). Corrected AG = AG + 2.5 × (4 − albumin g/dL).
Limitations and when not to rely on this result
- Educational estimate only; not a diagnosis, prescription, or treatment plan.
- Result depends on accurate inputs and may not apply to complex medical situations.
- Use clinician judgment, local guidance, and urgent care pathways when symptoms are severe.
Frequently asked questions
Should potassium be included in the anion gap? +
Some formulas include potassium and some do not. Use the same method as your local lab or teaching reference.
Why correct for albumin? +
Albumin is a major unmeasured anion, so low albumin can hide an elevated anion gap.
What is a normal anion gap? +
Normal ranges vary by lab and by whether potassium is included. Interpret against local reference ranges.
Can this diagnose metabolic acidosis? +
No. Diagnosis requires pH, bicarbonate, clinical context, lactate/ketones, renal function, and other data.
What if albumin is above 4? +
The correction formula can lower the corrected result, but clinical interpretation should follow local practice.