Which cardiac marker is raised first in myocardial infarction?

TMC Staff Nurse - 2019

Medical & Surgical Nursing

Easy

Appeared in: TMC Staff Nurse - 2019

Explanation

Myoglobin is the correct answer as it is the earliest cardiac biomarker to be released into the bloodstream following myocardial injury.
Due to its small molecular size, myoglobin is released rapidly from damaged cardiac muscle cells.
Its levels typically begin to rise within 1 to 4 hours after the onset of symptoms of an acute myocardial infarction (AMI).
This early appearance makes it a sensitive marker for detecting MI in the first few hours, although it lacks cardiac specificity.

Option A: CK-MB (Creatine Kinase-MB) begins to rise later than myoglobin, typically 3-6 hours after the onset of myocardial injury.
Option B: SGOT (Serum Glutamic-Oxaloacetic Transaminase), also known as AST (Aspartate Aminotransferase), is an outdated and non-specific cardiac marker. It rises much later, typically 6-12 hours after an MI, and is also found in many other tissues like the liver.
Option D: Troponin (T or I) is the most cardiac-specific biomarker, but it rises later than myoglobin, typically appearing in the blood 3-6 hours after the onset of an MI.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain The sequence and timeline of cardiac biomarker elevation following a myocardial infarction (MI) as background academic context rather than a clinical decision trigger.
Nurses must understand the different time courses of cardiac markers to correctly interpret lab results in the context of a patient's symptom timeline and report critical values promptly.
While myoglobin is the earliest marker, its low specificity means a positive result must be confirmed with a more specific marker like troponin. However, a negative myoglobin result in the early hours can be useful for ruling out an MI.
Troponin is the cornerstone of MI diagnosis. Serial troponin measurements (e.g., at presentation, 3 hours, and 6 hours) are standard practice to detect a rise and/or fall pattern, which confirms acute myocardial injury.

How to Approach the Question

First, identify the key phrase in the question: 'raised first'. This indicates the question is about the chronological sequence of events.
This is a factual recall question that requires knowledge of the pathophysiology of myocardial infarction and the associated biomarkers.
Mentally review the timeline of release for the common cardiac markers provided in the options.
Recall that smaller molecules are released more quickly from damaged cells. Myoglobin is a much smaller protein than CK-MB or Troponin.
Compare the onset times: Myoglobin (1-4 hours), CK-MB (3-6 hours), Troponin (3-6 hours), and SGOT (6-12 hours).
Select the marker with the earliest onset time, which is Myoglobin.

Concept Tested & Keywords

Concept Tested: The sequence and timeline of cardiac biomarker elevation following a myocardial infarction (MI).
Stem keywords: cardiac marker, myocardial infarction
Lead-in keywords: raised first

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