Interpretations

Serial measurements may be necessary to confirm or exclude the diagnosis of acute coronary syndrome. Repeat testing in 2 hours if clinically indicated.

Cardiac Troponin I (cTnI) is very specific to myocardium and not expressed during any developmental stage in skeletal muscle. Increased levels of cTnI are detected with myocardial injury. Detection of rise and/or fall of cTnI are essential to establish the diagnosis of acute myocardial infarction (MI). An increased cTnI concentration is defined as a value exceeding the upper reference limit of the 99th percentile of a normal reference population and is designated as the decision limit for the diagnosis of acute MI (Third Universal definition of Myocardial infarction, ESC/ACCF/AHA/WHF Expert consensus document. Circulation 2012; 126: 2020). Demonstration of rising and/or falling pattern is required to distinguish acute from elevations of cTnI levels that are associated with chronic heart diseases.

A positive cTnI result therefore, is not always indicative of ischemia. Other conditions resulting in myocardial cell damage can contribute to elevated cTnI include, but are not limited to:

Elevated Tnl Values in Patients Without AMI

Cardiac conditions

•  Angina/Unstable Angina

•  Atrial fibrillation

•   Cardiac surgery

•  Cardiomyopathy

•  Congestive heart failure

•  Coronary artery disease

•   Heart failure

•   Hypertensive urgency

•   Myocarditis

•   Pericarditis

•  Pulmonary emoblism

•   Recent cardiac intervention

•   Severe valvular heart disease

•   Tachycardia

Non-cardiac conditions

•   Chronic lung disease

•   Cardiac contusion related to a traumatic injury

•   Renal failure

•   Pneumonia

•   Pulmonary embolism

For assessing acute MI, blood samples should be drawn at the time of admission and repeated at 3 to 6 hours intervals. On certain occasions additional samples between 12 and 24 hours may be required if earlier measurements are not elevated and clinical suspicion is high for MI.

Nationally, there is no consensus on whether elevated troponin ought to be called to the ordering clinician as a critical value. It is widely acknowledged that laboratory results requiring critical value callback take longer to appear in the medical record. As Marshfield Clinic was an early adopter of electronic medical records, it is not surprising that reporting efficiency has taken precedence over person-to-person contact for elevated troponin levels. In other words, when myocardial injury or infarction is suspected, the ordering provider is awaiting the troponin value, and patients are generally not released before a result is reported. This is in contrast to critical values such as low platelet count or potassium level (placement of a CBC or electrolyte order does not mean that a clinician is expecting a medically emergent result, so the critical value policy ensures information is received in a timely manner). The laboratory has optimized assay workflow for rapid reporting of troponins and therefore will not call abnormal TNI results.

At the request of an inquiring clinician, the policy was reviewed July 2022 with laboratory professionals and practicing physicians, including clinicians in leadership roles Clinic-wide (Institution for Quality, Innovation and Safety and Board of Directors). The consensus opinion is that in standard of care medical practice, providers ordering a troponin in the outpatient setting, based on concern for myocardial injury, and should monitor patients in the clinic until a result is available. As such, the laboratory's role in optimizing patient care is to strive for highest accuracy and turn-around time, and to be available to answer clinician questions about the troponin assay and results, rather than interfering with the efficiency of the current reporting process.