Preferred biochemical markers in patients presenting with myocardial infarction September 2008
**Core Concept**
Troponin and creatine kinase (CK)-MB are highly sensitive and specific biochemical markers for diagnosing myocardial infarction (MI). These markers are released from damaged cardiac myocytes into the bloodstream, allowing for early detection and diagnosis of MI.
**Why the Correct Answer is Right**
The release of troponin and CK-MB into the bloodstream is a result of the breakdown of cardiac myocytes due to ischemia and necrosis. Troponin, specifically troponin T and troponin I, is a complex of three proteins that regulate muscle contraction in cardiac myocytes. CK-MB, a subunit of the creatine kinase enzyme, is also released from damaged cardiac myocytes. Elevated levels of these markers indicate cardiac damage and are highly specific for MI.
**Why Each Wrong Option is Incorrect**
**Option A:** Although lactate dehydrogenase (LDH) is an enzyme released from damaged cardiac myocytes, it is not as specific or sensitive as troponin and CK-MB for diagnosing MI.
**Option B:** Aspartate aminotransferase (AST) is an enzyme released from damaged liver and cardiac myocytes, but it is not specific for MI and can be elevated in various other conditions.
**Option C:** Myoglobin is a protein released from damaged cardiac myocytes, but it is not specific for MI and can be elevated in other conditions such as rhabdomyolysis.
**Option D:** Lipase is an enzyme released from the pancreas, and elevated levels are associated with acute pancreatitis, not MI.
**Clinical Pearl / High-Yield Fact**
Remember that troponin is the most sensitive and specific marker for MI, and a single elevated value can be diagnostic. However, CK-MB is still used in combination with troponin to confirm the diagnosis and assess the extent of cardiac damage.
**Correct Answer:** C. Myoglobin