Serum or plasma myoglobin levels are used as?

• A. An early marker of acute myocardial infarction
• B. Liver function tests
• C. Lead poisoning indicator
• D. Indicator of congestive heart failure

Answer: (A)

Myoglobin in serum or plasma is a signal of muscle injury, and its rapid release into the blood after muscle cell damage makes it an early indicator of myocardial infarction. After the heart muscle is injured, myoglobin levels rise very quickly—often within an hour or two of symptom onset and they peak within several hours—so it can help detect MI very early, before more specific markers rise. However, because myoglobin is found in both cardiac and skeletal muscle, it isn’t specific to the heart, so it’s not used alone to diagnose MI today; troponins are preferred for specificity, with myoglobin sometimes used as an adjunct in the very early window.

The other options don’t fit because myoglobin is not used to assess liver function, lead exposure, or congestive heart failure. Liver function tests rely on enzymes like AST/ALT, lead poisoning is assessed by measuring blood lead levels and related tests, and congestive heart failure is mainly evaluated using markers like BNP/NT-proBNP and imaging, not myoglobin.