What is the significance of repeating troponin (cardiac biomarker) levels in emergency medicine?

From the Guidelines

Repeat troponin testing in emergency medicine should be performed at 0,3, and 6 hours from presentation for patients with suspected acute coronary syndrome, with consideration of high-sensitivity troponin assays allowing for a 0 and 2-hour protocol. The specific timing depends on the assay used at your institution, with conventional troponin requiring longer intervals between measurements compared to high-sensitivity assays 1. When interpreting results, both absolute values and the delta change between measurements are important, with a significant delta (typically >20% for elevated values) suggesting acute myocardial injury 1.

Key Considerations

• The 99th percentile upper reference limit should be used to define myocardial injury, with sex-specific limits considered for optimal diagnosis and risk stratification 1.
• Clinical decision pathways should be integrated with high-sensitivity cardiac troponin (hs-cTn) results to facilitate diagnosis and risk stratification of patients with suspected acute coronary syndrome.
• Conditions such as type 2 myocardial infarction may become more common with the use of hs-cTn, while others like unstable angina may become less frequent but still occur 1.
• The limit of detection and the limit of quantitation of hs-cTn assays are crucial for clinical interpretation, especially in the single sample strategy to rule out acute myocardial infarction.

Interpretation of Results

• A troponin value above the 99th percentile of the upper reference level is required for the diagnosis of acute myocardial necrosis, along with evidence for a serial increase or decrease ≥20% if the initial value is elevated 1.
• For any troponin values below or close to the 99th percentile, evidence for acute myocardial necrosis is indicated by a change of ≥3 standard deviations of the variation around the initial value as determined by the individual laboratory 1.
• Absolute changes in nanograms per liter of high-sensitivity cardiac troponin T levels appear to have a significantly higher diagnostic accuracy for AMI than relative changes and may distinguish AMI from other causes of high-sensitivity cardiac troponin T elevations 1.

Clinical Implications

• Patients with negative serial troponins and low-risk features can often be safely discharged, while those with elevated or rising values require admission for further cardiac evaluation.
• The biological basis for serial testing relates to the delayed release of troponin after myocardial injury, with detectable levels appearing 3-4 hours after injury and peaking at 24-48 hours, necessitating repeat measurements to capture evolving myocardial damage that might be missed on a single test 1.

From the Research

Emergency Medicine Repeat Troponin

• The use of high-sensitivity troponin measurements is the preferred test to evaluate for non-ST-segment elevation myocardial infarction (NSTEMI) 2.
• Troponin levels are commonly used to diagnose acute coronary syndrome (ACS), which includes unstable angina, non-ST elevated myocardial infarction (MI), or ST-elevated MI 3.
• The presence of a cardiac-specific troponin in the circulation at levels above normal is good evidence of damage to cardiac muscle cells, such as myocardial infarction 4.
• Elevated troponin levels without ST-segment elevation on electrocardiography suggest non-ST-segment elevation ACS 5.
• In patients with acute stroke and elevated troponin levels, a thorough diagnostic workup is necessary to estimate the probability for a thrombotic myocardial infarction and to prevent cardiac and neurologic complications 6.

Troponin Assays

• Troponins are released as complexes leading to various cut-off values depending on the assay used, making them very sensitive and specific indicators of cardiac injury 4.
• The diagnostic window for troponin is longer than creatine kinase, remaining elevated for 7-10 days after acute myocardial infarction 4.
• Observation of a rise and fall in troponin levels in the appropriate time-frame increases the diagnostic specificity for acute myocardial infarction 4.

Clinical Use

• Early risk stratification can assist clinicians in determining whether an early invasive management strategy or an initial conservative strategy should be pursued, and can help determine appropriate pharmacologic therapies 3.
• Key components in the management of ACS include coronary revascularization when indicated, prompt initiation of dual antiplatelet therapy and anticoagulation, and consideration of adjuvant agents including β blockers, inhibitors of the renin angiotensin system, and HmG-coenzyme A reductase inhibitors 3.
• Patients with ACS should receive coronary angiography with percutaneous or surgical revascularization, as well as initiation of dual antiplatelet therapy and parenteral anticoagulation, statin therapy, beta-blocker therapy, and sodium-glucose cotransporter-2 inhibitor therapy 5.