CARDIAC ENZYMES - plasma or serum

---

This term is sometimes used to denote CREATINE KINASE (CK) with its MB isoenzyme (CKMB), ASPARTATE AMINOTRANSFERASE (AST) and LACTATE DEHYDROGENASE (LD). This combination of tests is not recommended for the diagnosis of uncomplicated myocardial infarction (MI). Cardiac troponin T or I is the test of choice. It is normally undetectable in plasma, but is reliably elevated after myocardial infarction. About 20% of patients with MI have elevated levels within 4-6 hours, and >95% after 12 hours. In MI, the level remains elevated for about 7 days. In unstable angina, the level is usually elevated, although to a lesser degree, and more transiently.

If the onset of pain is 4-8 hours prior to blood collection, myoglobin, if available, is a very sensitive but non-specific test. It can be used to exclude MI but, if elevated, definitive diagnosis with cardiac troponin T or I is needed.

Reference: Hamm CW. N Engl J Med 1994; 331: 607-608.

---