From the Guidelines
Troponin levels should be measured at presentation and then repeated 3-6 hours later in patients with suspected acute coronary syndrome. This recommendation is based on the highest quality evidence available, including the 2014 AHA/ACC guideline for the management of patients with non-ST-elevation acute coronary syndromes 1.
Key Considerations
- If the initial troponin is negative but clinical suspicion remains high, a third measurement at 6-12 hours may be necessary, as troponin levels may not be elevated immediately following cardiac injury.
- High-sensitivity troponin assays may allow for more rapid protocols with measurements at 0 and 2-3 hours.
- For patients presenting very early after symptom onset (less than 2 hours), an additional measurement beyond the 3-6 hour mark might be required since troponin can take time to rise.
- Serial measurements are important because troponin levels may not be elevated immediately following cardiac injury, as the protein takes time to leak into the bloodstream after myocardial damage.
Clinical Context
The timing of these measurements helps clinicians distinguish between acute myocardial infarction and other causes of chest pain, while also allowing them to observe the characteristic rise and/or fall pattern of troponin that is diagnostic of acute myocardial injury. If using point-of-care troponin tests with lower sensitivity, more conservative timing with measurements spaced further apart may be necessary. The evidence from the guidelines 1 supports the use of troponin measurements as a key diagnostic tool in the management of patients with suspected acute coronary syndrome.
Diagnostic Approach
The diagnostic approach should consider the clinical presentation, electrocardiographic changes, and the results of serial troponin measurements. The guidelines recommend measuring cardiac-specific troponin (troponin I or T) at presentation and 3 to 6 hours after symptom onset in all patients who present with symptoms consistent with ACS to identify a rising and/or falling pattern of values 1. 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.
From the Research
Frequency of Troponin Checks
The frequency of troponin checks in patients with suspected acute coronary syndrome (ACS) can vary depending on the clinical presentation and risk factors.
- Studies have shown that high-sensitivity cardiac troponin I assays can be used to identify low-risk patients who can be discharged from the hospital early 2.
- A study published in 2017 found that a 2-hour troponin check can be safe and effective in evaluating high-risk patients with suspected ACS, with a negative predictive value of 98.7% 3.
- Another study published in 2016 found that high-sensitivity troponin T (HsTnT) can be used to exclude non-ST elevation myocardial infarction (NSTEMI) within 3-4 hours of presentation in elderly patients, but cannot be used to rule in NSTEMI during this time period 4.
Timing of Troponin Checks
The timing of troponin checks is also important in diagnosing ACS.
- A study published in 2012 found that a point-of-care troponin I assay can be used to diagnose acute myocardial infarction (AMI) within 3 hours of presentation, with a sensitivity of 84.1% and a specificity of 93.4% 5.
- Another study published in 2011 found that a twofold or higher increase in troponin levels within 3-6 hours can indicate a high risk of AMI, with an odds ratio of 19 for troponin T and 8 for troponin I 6.
Clinical Implications
The frequency and timing of troponin checks have important clinical implications for patients with suspected ACS.
- Early identification of low-risk patients can lead to reduced hospital admissions and improved patient outcomes 2.
- The use of high-sensitivity troponin assays can help to exclude or confirm ACS, but requires careful interpretation of results in the context of clinical presentation and risk factors 3, 4, 5, 6.