Which cardiac marker is detected within 1-2 hours after an acute myocardial infarction (MI) and has low specificity?

Myoglobin is a small oxygen-binding protein found in muscle tissue, and its levels can increase in the blood within 1 to 2 hours following an acute myocardial infarction (MI). This rapid release makes myoglobin an early marker for diagnosing MI. However, its low specificity stems from the fact that myoglobin is not exclusive to cardiac tissue; it is also released from skeletal muscle during injury or stress. This characteristic means that elevated myoglobin levels may occur in conditions unrelated to heart attacks, such as muscle trauma, strenuous exercise, or rhabdomyolysis, leading to potential false-positive results in diagnosing an acute MI.

In contrast, troponin, while being a more specific marker for cardiac muscle injury, is typically detected later, usually about 3-4 hours after an MI onset. Creatine Kinase MB (CK-MB) and Lactate Dehydrogenase (LDH) also have their uses in cardiac diagnostics but share similar timing and specificity issues as troponin. CK-MB rises later than myoglobin, while LDH is more of a late indicator. Therefore, myoglobin is uniquely noted for its rapid increase and lower specificity, making it the correct choice in this context.