What Does Anion Gap Mean on a Blood Test?

What it means

The anion gap is not measured directly. The lab works it out from electrolytes on the same sample, usually sodium minus the total of chloride and bicarbonate, sometimes with potassium added. Blood contains positively and negatively charged particles that should balance. The gap stands for the negatively charged particles the standard panel does not measure, such as albumin and certain acids.

Labs print the anion gap because it helps doctors sort out acid-base problems. When extra acids build up in the blood, as in diabetic ketoacidosis, lactic acidosis, kidney failure or some poisonings, the gap tends to widen. A low gap is less common and is often linked to low albumin or to a measurement issue. In hospital it may be checked often because it can change quickly.

The anion gap is different from the pH or bicarbonate on a blood gas report, though they are related. Labs use slightly different formulas, so the range printed on your own report is the one to compare with.

Where you may see it

• Basic and comprehensive metabolic panels, after sodium, chloride and bicarbonate
• Emergency department and hospital blood results
• Hospital notes about diabetic ketoacidosis or other acid problems