The Most sensitive marker of cardiac injury is
**Core Concept**
The question is testing the knowledge of biomarkers for cardiac injury. Cardiac biomarkers are substances produced by the heart that can be measured in the blood to diagnose or monitor cardiac conditions. The most sensitive marker of cardiac injury is a biomarker that can detect even small amounts of cardiac damage.
**Why the Correct Answer is Right**
The correct answer is Troponin. Troponin is a protein complex that plays a crucial role in muscle contraction. In the heart, troponin is released into the bloodstream when cardiac muscle is damaged, such as in the case of a heart attack. Troponin is highly specific to the heart and can detect even small amounts of cardiac damage, making it the most sensitive marker of cardiac injury. This is because troponin is not found in significant amounts in other tissues, unlike other cardiac biomarkers such as creatine kinase (CK).
**Why Each Wrong Option is Incorrect**
**Option A:** CK-MB is a subunit of the enzyme creatine kinase, which is found in the heart and other tissues. While CK-MB is a useful marker of cardiac damage, it is not as sensitive as troponin because it can also be elevated in other conditions, such as muscle damage.
**Option B:** Myoglobin is a protein that is found in all muscle tissue, including the heart. While myoglobin can be elevated in cardiac damage, it is not as specific or sensitive as troponin because it can also be elevated in other conditions, such as muscle strain or rhabdomyolysis.
**Option C:** LDH (lactate dehydrogenase) is an enzyme that is found in many tissues, including the heart. While LDH can be elevated in cardiac damage, it is not as specific or sensitive as troponin because it can also be elevated in other conditions, such as liver or muscle damage.
**Clinical Pearl / High-Yield Fact**
Remember that troponin is the most sensitive marker of cardiac injury, but it can remain elevated for up to 2 weeks after a heart attack. This is why serial measurements of troponin are often used to diagnose or monitor cardiac conditions.
**Correct Answer:** T. Troponin.