Biomarker to rise earliest in myocardial infarction is: March 2010
**Core Concept**
The question is testing the knowledge of biomarkers used in the diagnosis of myocardial infarction (MI), specifically which one rises earliest. Biomarkers are molecules whose presence or concentration level in the blood can indicate a particular disease or condition. In the context of MI, biomarkers are used to confirm the diagnosis and assess the extent of cardiac damage.
**Why the Correct Answer is Right**
Troponin is a biomarker that is highly specific for cardiac muscle damage. It is released into the bloodstream within 2-3 hours after the onset of MI and peaks at 12-24 hours. Troponin is composed of three subunits (TnI, TnC, and TnT), and the TnT subunit is the most commonly measured. The TnT assay is highly sensitive and specific for MI, making it the preferred biomarker for diagnosing cardiac damage.
**Why Each Wrong Option is Incorrect**
**Option A:** Myoglobin is a biomarker that rises earlier than troponin, but it is less specific for cardiac muscle damage. Myoglobin is released from damaged skeletal muscle as well, so it is not a reliable marker for MI.
**Option B:** Creatine kinase (CK) is an enzyme that is released from damaged cardiac muscle, but it is not as sensitive or specific as troponin. CK-MB is the isoform of CK that is specifically measured in the context of MI, but it still has limitations compared to troponin.
**Option C:** Lactate dehydrogenase (LDH) is an enzyme that is released from damaged cardiac muscle, but it is not specific for MI. LDH is elevated in many conditions, including skeletal muscle damage, liver disease, and hemolysis.
**Option D:** Aspartate aminotransferase (AST) is an enzyme that is primarily associated with liver damage, but it can also be elevated in cardiac muscle damage.
**Clinical Pearl / High-Yield Fact**
Remember the "3-hour rule" for troponin: it takes at least 3 hours for troponin to rise significantly after the onset of MI. This delay is important to keep in mind when interpreting troponin levels in patients with suspected MI.
**Correct Answer: A. Myoglobin**