From the Guidelines
The correct timing for measuring high-sensitivity troponin T (hs-TnT) levels in patients presenting with chest pain is at presentation (0 hours) and again at 1 to 3 hours after presentation, as recommended by the 2021 AHA/ACC/ASE/CHEST/SAEM/SCCT/SCMR guideline 1. This guideline suggests that for high-sensitivity troponin assays, repeat measurements should be taken 1 to 3 hours after the initial sample collection. The use of high-sensitivity troponin assays allows for earlier detection of myocardial injury and can help reduce the time to diagnosis and treatment. Key points to consider when interpreting hs-TnT levels include:
- A single hs-cTn concentration below the limit of detection on initial measurement can be used to exclude myocardial injury in patients with acute chest pain, a normal ECG, and symptoms suggestive of ACS that began at least 3 hours before ED arrival 1.
- The 0-hour and 1-hour or 2-hour measurements may be used in some centers with validated high-sensitivity assays, but the 1 to 3-hour protocol is the recommended standard 1.
- A significant rise or fall in troponin levels between measurements is more specific for acute myocardial infarction than a single elevated value.
- Patients with a strong clinical suspicion of acute coronary syndrome but negative initial troponin results should still undergo the complete testing protocol to ensure myocardial infarction is not missed. It's also important to note that the 2021 guideline recommends institutions to implement a chest pain diagnostic protocol (CDP) that includes a protocol for troponin sampling based on their particular assay 1. In clinical practice, the choice of timing for measuring hs-TnT levels should be guided by the individual patient's presentation and clinical suspicion of ACS, as well as the availability of validated high-sensitivity assays. However, the 1 to 3-hour protocol remains the recommended standard for measuring hs-TnT levels in patients presenting with chest pain, as it allows for sufficient time to detect changes in troponin levels and provides a balance between sensitivity and specificity for diagnosing myocardial injury 1.
From the Research
Correct Timing for Measuring High-Sensitivity Troponin T (hs-TnT) Levels
The correct timing for measuring high-sensitivity troponin T (hs-TnT) levels in patients presenting with chest pain is crucial for accurate diagnosis and treatment.
- Studies have shown that measuring hs-TnT levels at 0 and 2 hours after presentation, together with ECG results, can identify patients suitable for early stress testing with a false negative rate for AMI of 1.2% 2.
- Another study found that a single sensitive troponin I assay on admission had a negative predictive value of 84.1% and a positive predictive value of 86.7% in patients presenting within 3 hours after chest-pain onset 3.
- The use of a high-sensitive troponin T assay can improve the early diagnostic accuracy of acute myocardial infarction (AMI) compared to conventional troponins, with a sensitivity of 96% and specificity of 85% on admission 4.
- A 1-hour rule-out high-sensitive troponin T protocol has been implemented in European guidelines, which has been shown to be safe in low-risk patients, with no AMIs or deaths occurring after introducing the protocol 5.
- A recent study found that a high sensitivity troponin under the 99th percentile upper reference limit drawn at 6 h or greater from symptom onset could safely rule out acute coronary syndrome in patients who did not meet the rapid rule-out strategy 6.
Observing Dynamics of Change of Troponin Levels
To observe the dynamics of change of troponin levels, the following points should be considered:
- Measuring hs-TnT levels at 0 and 2 hours after presentation can help identify patients with AMI 2.
- A delta of ≥20% over the 2-hour period for 0-2 hour samples can increase specificity to 92.4%, but reduces sensitivity to 56.1% 2.
- The use of a high-sensitive troponin T assay can improve the early diagnostic accuracy of AMI, with a sensitivity of 96% and specificity of 85% on admission 4.
- Measuring high sensitivity troponin at 6 hours or greater from symptom onset can safely rule out acute coronary syndrome in patients who do not meet the rapid rule-out strategy 6.