What laboratory test becomes abnormal at the earliest stage of acute coronary syndrome?

The test that becomes abnormal at the earliest stage of acute coronary syndrome is myoglobin. Myoglobin is a small, oxygen-binding protein found in heart and skeletal muscle. In the event of myocardial injury, myoglobin is released into the bloodstream quickly, leading to detectable levels within hours of an acute coronary event.

This rapid increase in myoglobin levels makes it a useful marker for early diagnosis of acute coronary syndrome, allowing for prompt clinical decision-making. Other markers, such as CK-MB isoforms, take longer to rise post-injury, typically appearing several hours after the event. High-sensitivity C-reactive protein is a marker of inflammation and can indicate cardiovascular risk but is not specific for acute coronary syndromes and does not rise immediately in response to myocardial injury.

Myosin light chain 1 may be associated with cardiac events, but it is not commonly used as a frontline marker for diagnosing acute coronary syndromes and does not rise as promptly as myoglobin. Thus, myoglobin is the most useful and early biomarker in the context of acute coronary syndrome.