Which biomarker is not an enzyme but rises earlier than CK-MB in AMI?

• A. Myoglobin
• B. CK-MB
• C. Troponin I
• D. LDH

Answer: (A)

The key idea is biomarker timing after heart injury and how enzymes differ from non-enzymes. Myoglobin is not an enzyme; it’s a small heme protein released quickly from damaged muscle, including the heart. Because of its rapid release, myoglobin becomes detectable in blood about 1–3 hours after onset of myocardial infarction, peaks around 6 hours, and returns toward baseline within about a day. CK-MB, in contrast, is an enzyme specific to heart muscle that rises later—typically around 4–6 hours after onset, peaks around 18–24 hours, and remains elevated longer. LDH is another enzyme that rises even later. Troponin I is not an enzyme either, but its rise occurs after injury and commonly overlaps with or follows CK-MB elevations.

So, among non-enzymes, myoglobin is the earliest marker to rise before CK-MB, making it the best answer for this question. Remember, its lack of cardiac specificity is a limitation, which is why clinicians use it in combination with troponin measurements for a reliable diagnosis.