Cardiac Medicine Certification (CMC) Practice Exam

Which laboratory test is less specific for heart muscle damage compared to troponin?

1. C-reactive protein

2. CK-MB

3. Myoglobin

4. Hematocrit

The correct answer is: CK-MB

The correct choice focuses on CK-MB, which stands for creatine kinase-MB. While CK-MB is a cardiac enzyme used in the diagnosis of myocardial infarction, it is less specific to heart muscle damage compared to troponin. Troponin is a protein associated specifically with cardiac muscle contraction, and its elevated levels are strongly indicative of cardiac injury, particularly myocardial infarction. In contrast, CK-MB can be elevated in various situations, including skeletal muscle damage or conditions that affect muscles outside the heart. This broader applicability reduces its specificity for diagnosing heart muscle damage compared to troponin, which remains highly specific. Other options, such as C-reactive protein and myoglobin, have their own roles and contexts in which they are utilized. Myoglobin, for instance, can be elevated in a variety of muscle injuries, not solely from the heart, although it does rise earlier than troponin in acute settings. C-reactive protein is predominantly a marker of inflammation and does not specifically indicate heart muscle damage. Hematocrit is related to blood volume and does not provide information about cardiac muscle injury.