Anion gap
A number calculated from your electrolytes that helps make sense of acid problems in the blood. When the blood is too acidic (metabolic acidosis), a high anion gap points to added acids — like the ketones of diabetes or lactate — narrowing down the cause.
What it measures
The anion gap is not measured directly but calculated from the routine electrolytes — essentially sodium minus the sum of chloride and bicarbonate. It reflects the balance of charged particles in the blood that aren't routinely measured. Its value is almost entirely in working out the cause of a metabolic acidosis — a state where the blood has become too acidic, usually detected first as a low bicarbonate. Acidosis splits into two useful groups based on the anion gap. A high anion gap acidosis means an acid has been added to the blood: the classic causes are the ketones of diabetic ketoacidosis, lactate (from poor tissue oxygen, as in shock or sepsis), the toxins from kidney failure, and certain poisonings (like aspirin overdose or antifreeze). A normal anion gap acidosis instead usually reflects a loss of bicarbonate — for example from severe diarrhoea or certain kidney tubular problems. So the anion gap is a simple, powerful sorting tool that turns 'the blood is acidic' into a shortlist of specific causes.
What a high value can mean
- High-anion-gap metabolic acidosis — an acid has been added to the blood.
- Diabetic ketoacidosis — ketones; often with high glucose.
- Lactic acidosis — poor tissue oxygen, as in shock, sepsis or severe illness.
- Kidney failure — retained acids.
- Certain poisonings — aspirin (salicylate) overdose, methanol, ethylene glycol (antifreeze).
What a low value can mean
- A low anion gap is uncommon and usually not clinically important — occasionally seen with a low albumin or certain blood conditions.
- A normal gap with acidosis — points instead to bicarbonate loss (e.g. diarrhoea, kidney tubular problems).
When to discuss with a doctor
The anion gap is a doctor's calculation used to interpret a metabolic acidosis, not something to act on by itself. Its importance is that it narrows a low bicarbonate down to a cause: a high anion gap points toward serious, treatable problems such as diabetic ketoacidosis, lactic acidosis from severe illness, kidney failure, or a poisoning — several of which are emergencies. It is always interpreted with the clinical picture and the rest of the electrolytes and blood gases. If you have a metabolic acidosis with a high anion gap, the underlying cause needs prompt identification and treatment. Mediora.AI shows the anion gap alongside bicarbonate, chloride and sodium so the acid-base pattern is read together; the clinical interpretation belongs with your doctor.