Investigations

• bicarbonate ^c

Calculate the anion gap (Na- + KHC0 ₃ ) ^c

Why?

A normal anion gap makes DKA unlikely, and a low bicarbonate makes it very likely

Patient	Target Disorder and Reference Standard	Diagnostic Test	LR+ (95% CI)	Post-test Probability	LR- (95% CI)	Post-test Probability
suspected diabetic ketoacidosis c (pre-test probability: 14%)	diabetic ketoacidosis (elevated glucose, metabolic acidosis and ketonaemia)	anion gap > 16 mmol/l	6.3 (5.1 to 7.6)	51%	0.096 (0.049 to 0.19)	15%
		serum bicarbonate < 15 mmol/l	100 (42 to 240)	94%	0.16 (0.11 to 0.26)	2.6%