From the Guidelines
Repeat troponin testing is recommended at 0 and 3 hours from presentation for most patients with suspected acute coronary syndrome (ACS) in the emergency department, as supported by the 2021 AHA/ACC/ASE/CHEST/SAEM/SCCT/SCMR guidelines 1. For high-sensitivity troponin assays, the 0-3 hour protocol is most common, though some institutions may use a 0-2 hour or 0-1 hour protocol depending on the specific assay used. The rationale for serial testing is that troponin release may be delayed after the onset of myocardial injury, and a single negative result cannot reliably exclude ACS, particularly if the patient presented early after symptom onset 1. Some key points to consider when interpreting troponin results include:
- A troponin value above the 99th percentile of the upper reference level is required for the diagnosis of acute myocardial necrosis, along with evidence of a serial increase or decrease ≥20% if the initial value is elevated 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
- Troponin elevations may persist for up to 14 days or occasionally longer, and an increase of >20% of previous troponin levels or an absolute increase of high-sensitivity cardiac troponin T values may indicate reinfarction 1 If the initial troponin is negative but clinical suspicion remains high, a repeat test should be obtained even if symptoms have resolved. Patients with negative serial troponins but concerning symptoms may still require additional testing such as stress testing or coronary CT angiography before discharge. It is also important to note that solitary elevations of troponin cannot be assumed to be due to MI, as troponin elevations can be due to other conditions such as tachyarrhythmia, hypotension or hypertension, cardiac trauma, acute HF, myocarditis and pericarditis, acute pulmonary thromboembolic disease, and severe noncardiac conditions 1. Overall, the use of high-sensitivity cardiac troponin assays and clinical decision pathways can help to improve the diagnosis and management of patients with suspected ACS.
From the Research
Emergency Medicine Repeat Troponin
- The use of troponin levels is crucial in the diagnosis of acute coronary syndrome (ACS) 2, 3, 4, 5, 6
- Troponin levels greater than 99th percentile of the upper reference limit are consistent with ACS 2
- For patients with suspected ACS, electrocardiography should be performed immediately, and troponin levels should be measured using one of several recommended protocols 2, 3, 6
- High-sensitivity troponin measurements are the preferred test to evaluate for non-ST-segment elevation myocardial infarction (NSTEMI) 3
- Elevated troponin levels without ST-segment elevation on electrocardiography suggest non-ST-segment elevation ACS 6
- The diagnosis of ACS is based on a combination of clinical assessment, electrocardiogram, and cardiac troponin levels, as well as a review of past medical history 4
- Repeat troponin testing is necessary to confirm the diagnosis of ACS, as troponin levels may not be elevated at the time of presentation 5
Timing of Troponin Testing
- Troponin levels start to rise approximately 4-6 hours after the onset of acute myocardial infarction and peak at approximately 24 hours 5
- Troponin levels remain elevated for 7-10 days, giving a longer diagnostic window than creatine kinase 5
- Repeat troponin testing should be performed at intervals of 2-3 hours to confirm the diagnosis of ACS 2
Clinical Decision Making
- The use of clinical decision tools, such as the Thrombosis in Myocardial Infarction (TIMI) or HEART score, can help clinicians determine the risk of ACS and guide management decisions 2
- Patients with ACS should receive coronary angiography with percutaneous or surgical revascularization, as well as initiation of dual antiplatelet therapy and parenteral anticoagulation 3, 6