Anion Gap Calculator
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What is the Anion Gap?
The anion gap is a clinical calculation that represents the difference between measured cations (positively charged ions like sodium) and measured anions (negatively charged ions like chloride and bicarbonate). It helps identify unmeasured anions in the blood.
Evaluating Metabolic Acidosis
A high anion gap suggests an excess of unmeasured acidic anions, characteristic of conditions like diabetic ketoacidosis (DKA), lactic acidosis, renal failure, or specific toxic ingestions. A normal anion gap acidosis occurs with bicarbonate loss (e.g., severe diarrhea).
The Importance of Albumin Correction
In critically ill patients, low albumin is highly common. Since albumin carries a negative charge, a drop of 1 g/dL in serum albumin decreases the baseline anion gap by approximately 2.5 mEq/L. Correcting for albumin prevents clinicians from missing acidosis.
When to Seek Urgent Medical Attention
- Rapid, deep breathing (Kussmaul breathing) or difficulty catching breath.
- Severe confusion, extreme drowsiness, lethargy, or loss of consciousness.
- Nausea, persistent vomiting, or severe abdominal pain in a person with diabetes.
Frequently Asked Questions
A typical serum anion gap without albumin correction is 3 to 11 mEq/L (when using modern ion-selective electrode analyzers), though clinical labs establish their own references.
Albumin is the major unmeasured anion in blood. If albumin is low (hypoalbuminemia), the measured anion gap will appear falsely low, masking metabolic acidosis.
