There is no such thing as a routine Troponin

(Aotea News, December 2009)

Michael Crooke
Chemical Pathologist

Over the last year there have been increasing numbers of requests for troponin T in what appears to be a ‘screening’ mode. That is, the test is requested together with fasting glucose, lipids and other routine tests, with no clinical details provided and no indication of urgency.

This is an improper use of the test for troponin T.

The correct use is as a diagnostic aid in the context of a patient who has symptoms suggestive of an acute coronary syndrome (ACS). Even then, the usefulness of troponin testing in primary care is limited. Because of the time course of release of troponin T, a negative result cannot be used as a rule out test soon after symptoms. Even in those subjects who prove to have confirmed myocardial infarction, troponin will not have 100% sensitivity for up to 10 hours.

Thus, a clinical plan that includes measuring only a single early troponin is not recommended practice in the assessment of a patient with acute chest pain or other acute symptoms which may suggest an evolving ACS. Such patients should immediately be referred to A&E for evaluation in a formal chest pain protocol.

The best use for troponin in primary care is in the evaluation of a clinically stable patient who presents up to several days after symptoms that may have been atypical but which are still consistent with ACS. This is as stated in current bpac guidelines and a more detailed review of the role of troponins in primary care is pending.

http://www.bpac.org.nz/resources/campaign/cardiovascular/lab_cardio.asp

Although the prior probability of myocardial infarction will be low in most of these patients, raised troponin is found occasionally and can present the laboratory with a dilemma. When the result emerges after 5pm practices are often closed and sometimes we have no way to contact the requesting doctor with the information. Since a positive result indicates that a significant clinical event has occurred, we believe that the doctor should have the information to allow immediate reassessment and possible change of management. Even if the raised Troponin does not represent myocardial infarction, many of the other causes of raised Troponin, such as myocarditis, pericarditis or pulmonary embolism, may present with similar symptoms and also have significant morbidity and mortality.

When Troponin is correctly requested, it is not a routine request and the contact number of the requesting doctor or their deputy should be provided with the request, especially if it is likely that the result will become available only ‘after hours’.