Investigations

Calculate the urea: creatinine ratio: 

urea (in mmol/L): creatinine (in mol/L) ^c  

Why?

A urea: creatinine ratio > 0.1 makes pre-renal failure more likely

Patient c	Target Disorder and Reference Standard	Diagnostic Test	LR+ (95% CI)	Post-test Probability	LR- (95% CI)	Post-test Probability
suspected pre-renal failure (pre-test probability: 20%)	pre-renal failure (clinical records)	urea: creatinine ratio > 0.1	3.4 (1.5 to 8.0)	46%	0.53 (0.38 to 0.74)	12%