Anion Gap Calculator
The anion gap helps doctors find the cause of acid-base problems (acidosis) using routine electrolyte results.
These health tools are still being tested and are updated regularly to give you a better experience. Results are estimates for information only — please confirm important results with a doctor. Read the medical disclaimer
ProfessionalThis tool is meant for doctors, nurses and pharmacists. It supports, but does not replace, clinical judgement. Medicine doses must only be decided by a doctor or pharmacist.
Anion Gap Calculator
Next steps
- Kidney Function Test Reference GuideUnderstand creatinine, urea, uric acid, electrolytes and eGFR on your KFT report.
- Corrected Calcium CalculatorAdjust your total calcium for low albumin to get a truer picture of blood calcium.
- Blood Sugar Level Reference GuideNormal, prediabetes and diabetes ranges for fasting, after-meal, random and HbA1c tests.
- Signs of Dehydration and How to Prevent Water Deficiency in the BodyHealth guide
About the Anion Gap Calculator
This is a clinical tool mainly used by doctors and students. A high anion gap can point to conditions like diabetic ketoacidosis, kidney failure or certain poisonings.
How to use the Anion Gap Calculator
- Take sodium, chloride and bicarbonate from the same blood test (mEq/L = mmol/L).
- Optionally add albumin (g/dL) for the corrected gap, and potassium if your lab includes it.
- Press Calculate.
Formula explained
Anion gap = Na⁺ − (Cl⁻ + HCO₃⁻)
All values in mEq/L (mmol/L). A typical range is about 8–12 mEq/L, but it depends on the lab.
Albumin-corrected gap = anion gap + 2.5 × (4.0 − albumin g/dL)
Worked example: Anion Gap
Sodium 138, chloride 100 and bicarbonate 16 mEq/L give an anion gap of 138 − (100 + 16) = 22 mEq/L — high. With albumin 3.0 g/dL the corrected gap is 22 + 2.5 × 1.0 = 24.5 mEq/L.
Important limitations
- Normal ranges depend on the analyser used by the lab.
- Interpreted by doctors together with blood gases, glucose, ketones, lactate and kidney tests.
Frequently asked questions
What does a high anion gap mean?
It suggests extra acids in the blood, as in ketoacidosis, lactic acidosis, kidney failure or some poisonings. It always needs a doctor’s assessment.
Why correct for albumin?
Albumin is a major unmeasured anion. Low albumin lowers the anion gap and can hide a real problem, so the corrected value is more reliable.
What does “MUDPILES” mean?
It is a memory aid doctors use for causes of a high anion gap acidosis: methanol, uraemia (kidney failure), diabetic ketoacidosis, paraldehyde/propylene glycol, iron/isoniazid, lactic acidosis, ethylene glycol and salicylates. Newer versions include others.
Is a low anion gap serious?
Usually not. The most common cause is low albumin; lab error is another. Rarely, it is linked with conditions such as multiple myeloma, so doctors may check further if it persists.
Sources
- Figge J et al. Anion gap and hypoalbuminemia. Crit Care Med 1998;26:1807-10.
- Kraut JA, Madias NE. Serum anion gap: its uses and limitations. Clin J Am Soc Nephrol 2007;2:162-74.
Medical disclaimer: Acid–base problems can be serious. This tool supports, but cannot replace, assessment by a doctor. These tools give general information and estimates only. They are not a diagnosis and do not replace advice from a qualified doctor. Always talk to your doctor about your results, and seek urgent medical help in an emergency. In an emergency call 112. Medical disclaimer · Terms of use · Privacy policy
