Anion Gap Calculator — Free Online Calculator
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Anion Gap
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About This Calculator
The anion gap helps evaluate the cause of metabolic acidosis. It represents the difference between measured cations and anions in serum. An elevated anion gap suggests the presence of unmeasured anions, such as lactate, ketoacids, or toxic alcohols.
Formula
Interpretation
| Anion Gap (mEq/L) | Interpretation |
|---|---|
| < 8 | Low |
| 8 – 12 | Normal |
| > 12 | Elevated |
References
Frequently Asked Questions
What does a high anion gap indicate?
A high anion gap (>12 mEq/L) suggests the presence of unmeasured anions, typically from metabolic acidosis. Common causes include lactic acidosis, diabetic ketoacidosis (DKA), renal failure, and toxic ingestions (methanol, ethylene glycol, salicylates).
What is a normal anion gap?
The normal anion gap is typically 8–12 mEq/L when calculated as Na − (Cl + HCO₃). If potassium is included, the normal range shifts to 10–14 mEq/L. Labs using ion-selective electrodes may have slightly different reference ranges.
What is a non-anion-gap metabolic acidosis?
A non-anion-gap (or hyperchloremic) metabolic acidosis has a normal anion gap with low bicarbonate. Causes include diarrhea, renal tubular acidosis (RTA), and use of carbonic anhydrase inhibitors.
Should I correct the anion gap for albumin?
Yes. Albumin is the major unmeasured anion. In hypoalbuminemia, the anion gap may appear falsely normal. The corrected anion gap adds approximately 2.5 mEq/L for each 1 g/dL decrease in albumin below 4.0 g/dL.
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⚠ Medical Disclaimer
This tool is for educational and informational purposes only. It is not intended to replace professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare professional for clinical decisions.