Investigations

• serial cardiac enzymes, ideally CK-MB ^{b c}  

Why?

Early CK-MB rise diagnoses an MI and normal levels at 20 h rule it out

Patient	Target Disorder and Reference Standard	Diagnostic Test	LR+ (95% CI)	Post-test Probability	LR- (95% CI)	Post-test Probability
suspected myocardial infarction c (pre-test probability: 18%)	myocardial infarction (history, ECG, CK-MB act)	elevated CK-MB mass at 3 hours after symptom onset	infinity (16 to infinity)	100%	0.68 (0.61 to 0.75)	13%
		at 4 hours	28 (19 to 42)	86%	0.45 (0.39 to 0.52)	9%
		at 6 hours	29 (19 to 44)	86%	0.13 (0.11 to 0.16)	3%
		at 8 hours	19 (13 to 27)	81%	0.063 (0.053 to 0.076)	1%
		at 12 hours	14 (11 to 18)	75%	0.032 (0.027 to 0.039)	0.7%
		at 20 hours	11 (8 to 16)	71%	0.00 (0.0 to 0.020)	0%