When to repeat Troponin (Trop) I testing in patients with suspected acute myocardial infarction?

From the Guidelines

Troponin I testing should be repeated 3 to 6 hours after symptom onset in all patients who present with symptoms consistent with acute coronary syndromes (ACS) to identify a rising and/or falling pattern. This recommendation is based on the 2014 AHA/ACC guideline for the management of patients with non-ST-elevation acute coronary syndromes 1. The guideline suggests that cardiac-specific troponin levels should be measured at presentation and 3 to 6 hours after symptom onset.

Key Points to Consider

• The timing of repeat testing is crucial because troponin levels may not be elevated immediately after cardiac injury, as it takes time for the protein to be released into the bloodstream following myocardial damage.
• Additional troponin levels should be obtained beyond 6 hours after symptom onset in patients with normal troponins on serial examination when electrocardiographic changes and/or clinical presentation confer an intermediate or high index of suspicion for ACS 1.
• If the time of symptom onset is ambiguous, the time of presentation should be considered the time of onset for assessing troponin values 1.
• For patients presenting very early after symptom onset (less than 2 hours), an initial negative result should always be followed by repeat testing even if symptoms resolve.

Clinical Considerations

• Troponin typically begins to rise 3-4 hours after myocardial injury, peaks at 24-48 hours, and can remain elevated for 7-14 days.
• Serial measurements help distinguish between acute and chronic elevations and capture the dynamic changes characteristic of AMI.
• When interpreting results, it's essential to consider both the absolute values and the delta change between measurements, as a significant rise or fall (typically >20% change) supports the diagnosis of AMI.

High-Sensitivity Troponin Assays

• For high-sensitivity troponin assays, testing can be done at 0 and 2-3 hours, with some protocols allowing for even shorter intervals (0 and 1 hour) 1.

Conclusion Not Needed, Direct Answer Provided Above

From the Research

Timing of Troponin I Repeated Measurement

The decision to repeat Troponin I (Trop I) testing in patients with suspected acute myocardial infarction (AMI) depends on several factors, including the initial troponin level, the presence of chest pain or other symptoms, and the results of electrocardiogram (ECG) tests.

• If the initial troponin level is elevated, the measurement should be repeated within 3-6 hours 2.
• A twofold or higher increase in troponin levels implies a higher risk of AMI, with an 8-times odds ratio for troponin I 2.
• The use of sensitive troponin I assays can improve early diagnosis and risk stratification of AMI, regardless of the time of chest-pain onset 3, 4.
• A single sensitive troponin I assay on admission can have 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 1-hour rule-in and rule-out algorithm using high-sensitivity cardiac troponin I can safely rule out AMI in 50.5% of patients and accurately rule in AMI in 19% of patients 5.

Considerations for Repeated Measurement

When deciding whether to repeat Trop I testing, consider the following:

• The patient's accompanying diseases, which can cause chronic cardiac damage and elevate troponin levels 2.
• The presence of chest pain or other symptoms, which can indicate AMI 2, 3.
• The results of ECG tests, which can help diagnose AMI 2, 5.
• The initial troponin level, which can help determine the risk of AMI 2, 3.