Investigations

• serial creatine kinase (CK) ^{b c} , aspartate transaminase (AST) ^a , lactate dehydrogenase (LDH) ^a taken over 24 hours ^a

Why?

• 96% of MI can be diagnose at 24 hours using CK-MB, LDH, CK and ECG changes (95% CI: 95% to 98%) ^a  

Elevated creatine kinase levels diagnose myocardial infarction

Patient	Target Disorder and Reference Standard	Diagnostic Test	LR+ (95% CI)	Post-test Probability
suspected myocardial infarction c (pre-test probability: 64%)	myocardial infarction (ECG changes)	highest CK 280 IU/ or more	54 (7.7 to 380)	99%
		CK 80 to 279 IU/l	4.5 (2.7 to 7.3)	89%
		CK 40 to 79 IU/l	0.30 (0.16 to 0.56)	35%
		CK < 40 IU/l	0.013 (0.0032 to 0.051)	2.0%

Elevated AST levels taken 12 hours or more after symptom onset help diagnose myocardial infarction

Patient	Target Disorder and Reference Standard	Diagnostic Test	LR+ (95% CI)	Post-test Probability
central or left-sided chest pain a (pre-test probability: 41%)	myocardial infarction (ECG, cardiac enzymes, stress tests)	AST taken more than 12 hours after chest pain onset:100 IU/l or more	30	89%
		80 IU/l	2.3	39%
		60 IU/l	5.6	60%
		50 IU/l	0.40	10%
		40 IU/l	0.59	14%
		30 IU/l	0.32	8%
		< 30 IU/l	0.078	2%

• CK ^{a b} , AST ^a or LDH ^a taken within 12 hours of symptom onset cannot safely exclude a myocardial infarction.

Cardiac enzymes taken in the emergency department cannot diagnose or exclude a myocardial infarction

Patient	Target Disorder and Reference Standard	Diagnostic Test	LR+ (95% CI)	Post-test Probability	LR- (95% CI)	Post-test Probability
central or left-sided chest pain a (pre-test probability: 17%)	myocardial infarction (ECG, cardiac enzymes)	CK > 180	1.8 (1.3 to 2.5)	27%	0.77 (0.65 to 0.91)	14%
		AST > 60	6.1 (3.5 to 10)	56%	0.43 (0.29 to 0.64)	8%
		AST > 47	3.4 (2.3 to 5.1)	41%	0.44 (0.29 to 0.68)	8%
		LDH > 200	2.0 (- to -)	29%	0.59 (- to -)	11%
		CK or AST abnormal	1.7 (1.3 to 2.2)	26%	0.65 (0.51 to 0.82)	12%

CK levels alone taken at 24 hours cannot safely diagnose or exclude myocardial infarction

Patient	Target Disorder and Reference Standard	Diagnostic Test	LR+ (95% CI)	Post-test Probability	LR- (95% CI)	Post-test Probability
central or left-sided chest pain b (pre-test probability: 18%)	myocardial infarction (CK-MB at 24 hours)	elevated creatine kinase	6.0 (3.7 to 9.8)	57%	0.62 (0.50 to 0.76)	12%