Investigations

• troponin T ^{a b c} or troponin I ^c  

Why?

A normal troponin T at 20 hours makes an MI unlikely

Patient c	Target Disorder and Reference Standard	Diagnostic Test	LR+ (95% CI)	Post-test Probability	LR- (95% CI)	Post-test Probability
suspected myocardial infarction (pre-test probability: 18%)	myocardial infarction (history, ECG, CK-MB act )	elevated troponin T at 3 hours after symptom onset	6 (4 to 9)	57%	0.67 (0.59 to 0.76)	13%
		at 4 hours	11 (7 to 16)	71%	0.59 (0.52 to 0.67)	9%
		at 6 hours	7 (4 to 10)	61%	0.37 (0.31 to 0.43)	8%
		at 8 hours	9 (6 to 13)	66%	0.23 (0.19 to 0.27)	5%
		at 12 hours	9 (7 to 12)	66%	0.078 (0.064 to 0.94)	2%
		at 20 hours	9 (6 to 13)	66%	0.022 (0.019 to 0.027)	0.5%

Normal CK-MB and troponin I can help rule out MI

Patient c	Target Disorder and Reference Standard	Diagnostic Test	LR+ (95% CI)	Post-test Probability	LR- (95% CI)	Post-test Probability
chest pain lasting for at least 15 minutes within previous 24 hours (pre-test probability: 37%)	myocardial infarction (CK-MBmass at 24 hours)	troponin I at 6 hours	10 (7.3 to 14)	59%	0.45 (0.37 to 0.56)	6%
		at 18 hours	15 (11 to 19)	67%	0.045 (0.019 to 0.11)	1%