A 54 year old man comes to the emergency room four hours after the onset of severe chest pain radiating to the left arm. Examination of the levels of which of the following serum markers would best aid in the evaluation of this individual's chest pain?

Cardiac-specific forms of troponin-T and troponin-I are not normally detectable in the blood, but may increase 20-fold following a myocardial infarction. Slight amino acid differences between cardiac and skeletal muscle forms of troponin allow specific association of the troponin with hea muscle damage, rather than skeletal muscle damage. Troponin is the best serum marker for myocardial infarction for the first eight hours, and because levels of the cardiac troponins remain elevated for 7-10 days, it may be useful for evaluation of small, CK-negative infarctions for several days after the event. AST is a nonspecific marker for cardiac, liver, and skeletal muscle. Due to its lack of specificity, it is much less useful as a marker of myocardial infarction than CK-MB or troponin. Both total creatine kinase and its more cardiac specific form CK-MB are most useful from 8 to 24 hours after infarction, typically with peaks at 12-18 hours. LDH1, the cardiac specific form of lactic dehydrogenase, is the test of choice 2 to 7 days after a suspected myocardial infarction. Ref: Green G.B., Hill P.M. (2011). Chapter 52. Chest Pain: Cardiac or Not. In J.E. Tintinalli, J.S. Stapczynski, D.M. Cline, O.J. Ma, R.K. Cydulka, G.D. Meckler (Eds), Tintinalli's Emergency Medicine: A Comprehensive Study Guide, 7e.