Clinical tool
Anion Gap
Anion gap, with optional potassium and albumin correction.
Standard calculation leaves potassium out.
What this calculates
The anion gap: sodium minus chloride and bicarbonate, with potassium optionally included, and an optional correction for albumin.
When to use it
When assessing a metabolic acidosis, to help separate raised-gap from normal-gap causes.
How to interpret it
Without potassium the usual range is about 8 to 12 mmol/L, and with potassium about 12 to 16. A raised gap suggests added unmeasured anions such as lactate, ketones, uraemia or toxins. A normal gap with acidosis suggests bicarbonate loss or chloride excess.
Important limitations
- Low albumin lowers the gap and can hide a true raised gap, which is why the albumin-corrected value is shown when albumin is entered.
- Reference ranges depend on the analyser, so use your laboratory's range where it differs.
- A negative or very low gap is unusual. Consider measurement error, paraproteins or severe hypoalbuminaemia.
For practising medics only. Clinical tools support judgement, they do not replace it. Always verify results against current guidelines and the patient in front of you.