The anion gap reflects unmeasured anions in the blood and is a useful screen for metabolic acidosis. It is calculated as sodium minus the sum of chloride and bicarbonate — the gap represents anions such as albumin, phosphate, sulphate, and organic acids that are not directly measured. An elevated gap suggests the presence of an unmeasured acid (lactate, ketones, uraemic acids, toxins). The albumin-corrected value is essential when albumin is low, since hypoalbuminaemia reduces the normal gap and can mask an elevated AG — using the Figge correction ensures the result is interpreted against an appropriate baseline.
This tool is for reference only. Clinical decisions should always involve a qualified healthcare professional.