What is the proper use of troponin (cardiac biomarker) tests?

From the Guidelines

Troponin tests should be used to diagnose heart attacks by measuring troponin levels at presentation and 3 to 6 hours after symptom onset, with additional measurements beyond 6 hours if the initial results are normal and there is a high index of suspicion for acute coronary syndrome (ACS) 1. The proper use of troponin tests involves collecting a blood sample from the patient and sending it to a laboratory for analysis.

Key Points to Consider

• The test should be ordered when a patient presents with symptoms suggestive of a heart attack, such as chest pain, shortness of breath, or discomfort in the upper body.
• Multiple troponin measurements are typically taken over time (usually at presentation, then 3-6 hours later, and sometimes at 12 hours) to detect changes in levels, as troponin may not rise immediately after heart damage begins.
• Normal troponin levels are very low or undetectable in healthy individuals; elevated levels indicate heart muscle damage.
• The specific cutoff values for what constitutes "elevated" depend on the particular assay used by your laboratory.
• High-sensitivity troponin tests can detect smaller amounts of troponin and show abnormalities earlier than standard tests.
• When interpreting results, remember that while troponin elevation strongly suggests heart damage, it doesn't always mean a heart attack has occurred, as other conditions like severe infections, heart failure, or kidney disease can also cause elevated levels 1.

Clinical Considerations

• The diagnosis of acute myocardial infarction (AMI) includes the increase and/or decrease in the biomarker troponin; therefore, numerous studies have evaluated the effectiveness of different timelines for ruling in an AMI by using various troponin assays 1.
• The accuracy and test characteristics of troponins for ruling out an AMI is an area of interest, given the relatively new high-sensitivity troponin tests available.
• In patients with STEMI, reperfusion therapy should not be delayed pending results of biomarkers, and biomarkers are not useful in the prehospital setting 1.

Important Notes

• If biomarkers are initially negative within 6 hours of symptom onset, it is recommended that biomarkers should be remeasured between 6 to 12 hours after symptom onset.
• Clinicians should take into account the timing of symptom onset and the sensitivity, precision, and institutional norms of the assay, as well as the release kinetics and clearance of the measured biomarker.

From the Research

Proper Use of Troponin Tests

The proper use of troponin tests involves understanding their role in diagnosing and risk-stratifying patients with suspected acute coronary syndrome (ACS) [ 2, 3 ]. Key points to consider include:

• Troponin testing should be limited to patients presenting with ischemic symptoms that occurred more than 24 hours previously, and who have no high-risk clinical features and a normal electrocardiogram (ECG) [ 2 ].
• In patients presenting with symptoms of possible ACS within the preceding 24 hours, or with high-risk clinical features or ECG abnormalities, a serum troponin test should not be ordered, and patients should be referred immediately to an emergency department [ 2, 3 ].
• When a single troponin assay is appropriate, the test should be labeled as urgent, and systems must be in place to ensure the result is conveyed immediately to the medical practitioner [ 2 ].

Interpretation of Troponin Results

Interpreting troponin results requires clinical acumen, as elevated troponin levels can be seen in several non-coronary ischemia presentations [ 4 ]. Considerations include:

• Elevated troponin levels in the setting of ACS are diagnostic of acute myocardial infarction and provide guidance for intensive medical and revascularization therapies [ 4 ].
• The timing of troponin testing is fundamental to its clinical utility, and general practitioners should have a sufficient understanding of the test for use in primary care [ 5 ].

Role of Troponin Testing in Primary Care

The role of troponin testing in primary care is limited, and patients with symptoms suggestive of ACS should be referred to the hospital for early diagnosis and specialist care [ 3, 5 ]. Key points include:

• A single troponin test may be reasonable in primary care to exclude the possibility of acute myocardial infarction in asymptomatic low-risk patients whose symptoms resolved at least 12 hours prior [ 5 ].
• General practitioners should factor in the complex logistics of troponin testing in the community, including ensuring accurate and timely results [ 5 ].