What is the optimal timing for collecting troponin (cardiac biomarker) levels?

From the Guidelines

Troponin levels should be collected at presentation (0 hours) and then 3-6 hours later for patients with suspected acute coronary syndrome. For high-sensitivity troponin assays, a 0-hour and 1-3 hour protocol is often used, with some centers implementing rapid rule-out protocols using measurements at 0 and 1 hour 1. In patients with an initially negative troponin but strong clinical suspicion, a third sample at 6-12 hours may be warranted. Serial measurements are essential because troponin levels may not be elevated immediately after cardiac injury, as the protein takes time to leak into the bloodstream. The timing of peak troponin elevation varies by assay type, with conventional assays typically peaking at 12-24 hours and remaining elevated for 7-14 days, while high-sensitivity assays can detect elevations earlier 1. This serial testing approach helps distinguish acute myocardial injury from chronic elevations and provides information about the timing and extent of cardiac damage.

Some key points to consider when interpreting troponin levels include:

• The 99th percentile of the upper reference level is the appropriate cutpoint for considering myocardial necrosis 1
• A rise and/or fall of troponin measurements is essential to the diagnosis of acute myocardial infarction 1
• Troponin values may remain elevated for 7-14 days following the onset of infarction 1
• High-sensitivity troponin assays can detect elevations earlier than conventional assays 1

It's also important to note that troponin elevations can be due to various conditions other than acute coronary syndrome, such as cardiac contusion, congestive heart failure, and severe noncardiac conditions like sepsis or respiratory failure 1. Therefore, clinical correlation and consideration of other diagnostic factors are crucial in interpreting troponin levels.

In terms of specific protocols, the American College of Cardiology/American Heart Association (ACC/AHA) guidelines recommend measuring cardiac-specific troponin levels at presentation and 3-6 hours after symptom onset in all patients with suspected acute coronary syndrome 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 acute coronary syndrome 1.

From the Research

Optimal Timing for Collecting Troponin Levels

The optimal timing for collecting troponin levels can be determined based on the 0/2-hour algorithm, which uses high-sensitivity cardiac troponin I (hs-cTnI) assay to rapidly triage patients with suspected acute myocardial infarction (AMI) [ 2 ].

• The 0/2-hour algorithm measures hs-cTnI concentrations at presentation and after 2 hours, allowing for rule-out or rule-in of AMI [ 2 ].
• The rule-out criteria include a 0-hour hs-cTnI-Access concentration <4 ng/L in patients with an onset of chest pain >3 hours, or a 0-hour hs-cTnI-Access concentration <5 ng/L and an absolute change within 2 hours <5 ng/L in all other patients [ 2 ].
• The introduction of high-sensitivity cardiac troponin T (hs-cTnT) has been shown to improve the rule-out process, reducing the need for stress testing and time to discharge [ 3 ].

Diagnostic Process and Timing

The diagnostic process for suspected AMI should start as soon as possible, with elevation of a marker of myocardial necrosis, such as troponin T or I, being mandatory for diagnosis [ 4 ].

• Repeated measurements of markers of myocardial damage, including troponin, are necessary for diagnosis in patients without ST-segment elevation on admission [ 4 ].
• The 0/1-hour algorithm with a high-sensitivity cardiac troponin (hs-cTnI) assay has also been evaluated, showing high diagnostic sensitivity and negative predictive value for AMI [ 5 ].

Clinical Implications

The clinical introduction of high-sensitivity cardiac troponin assays has been associated with improved patient outcomes, including reduced time to discharge and lower costs [ 3 ].

• However, troponin elevation is commonly found in patients without AMI, and its association with greater use of echocardiography, coronary angiography, and percutaneous coronary intervention has been reported [ 6 ].
• The role of cardiac testing in the 3 zones (rule-out, observation, and rule-in) of the 0/1-hour algorithm has been evaluated, showing low diagnostic yield of noninvasive testing in rule-out zone patients [ 5 ].