Clinical significance of low-positive troponin I by AxSYM and ACS:180

Falsely elevated cardiac troponin I levels

The measurement of cardiac troponins (cTn) is of considerable usefulness in the diagnosis of acute coronary syndrome. Abnormal levels of serum cTn are occasionally found in patients who are not suffering a myocardial infarction. This may be observed in several well-known situations including pulmonary embolism, pericarditis, myocarditis, coronary vasospasm, sepsis, congestive heart failure, supraventricular tachycardia with hemodynamic compromise, re-nal insufficiency, and prolonged strenuous endurance exercise. Endogenous antibodies such as heterophile antibodies, rheumatoid factor, and other autoantibodies are known to interfere with the immunoassay measurements of many different analytes, including the widely used Abbot AxSYM cTnI analyzer. Other sources of circulating antibodies include immunotherapies, vaccinations, or blood transfusions that may interfere with these immunoassays as well. We examine the case of a 48-year-old man with a history of hypercholesterolemia and obesity who presented with chest pain and was found to have elevated Tn I levels on two separate occasions. Further work-up revealed that the Tn I levels were spuriously elevated because the patient's blood revealed a normal cTnI level when mixed with polyethylene glycol to inactivate any antibodies interfering with the cTnI assay.

British Cardiac Society Working Group on the definition of myocardial infarction

The British Cardiac Society commissioned this report to help address inconsistencies in the terminology for acute coronary syndromes and wide variations in the threshold for the diagnosis of myocardial infarction (MI) depending on the assay performed, the precision, and the sensitivity. In addition, several publications have highlighted potential problems with the application of the European Society of Cardiology(ESC)/American College of Cardiology (ACC) consensus document published in 2000. A revision process has been initiated under the guidance of the ESC, the ACC, and the American Heart Association (AHA). The purpose of this report is to help inform the next revision of the ESC/ACC/AHA guidelines for the diagnosis of MI.

Troponin I in Patients without Chest Pain

Background: Testing for troponin has important clinical value for patients who present with typical symptoms of acute coronary syndromes (ACS) such as chest pain (CP). Much less is known about the value of troponin testing for patients who present with other symptoms of ACS (anginal equivalent symptoms).

Methods: The utilization and prognostic value of cardiac troponin I (cTnI) were evaluated at a Veterans Affairs Acute Care Facility. Clinical charts of 1184 predominantly male patients, who submitted specimens for initial cTnI testing by AxSYM, were evaluated for demographic data, cardiovascular risk factors, major diseases, and complaints at the time of testing. The endpoint was defined as all-cause death during a 200-day period after initial testing.

Results: Sixty-one percent of cTnI tests were ordered for patients who did not present with CP. Patients presenting with symptoms other than CP did not have significantly lower plasma cTnI than patients with CP. However, patients with symptoms other than CP were rarely diagnosed with ACS unless cTnI was ≥2 μg/L. The mortality during the follow-up period was severalfold higher among patients presenting with symptoms other than CP (CP, 6%; without CP, 22%; P <0.0001, χ2 test). cTnI ≥0.2 μg/L provided significant additional predictive information for patients who presented with anginal equivalent symptoms such as shortness of breath or general weakness.

Conclusion: Patients with anginal equivalent symptoms of ACS and low-positive cTnI are less often diagnosed with ACS and have a higher mortality than patients with CP.

The measurement of cardiac markers: where should we focus?

Cardiac markers are presently a hot topic, with active debate on their use. They now have a major role for cost-effective management of acute chest pain and suspected acute coronary syndrome. The laboratory has a pivotal role in proper selection and interpretation of available markers, depending on the creation of evidence-based knowledge about test utilization and sources of variation. This article reviews this knowledge in the field of biomarkers determination and summarizes the major analytic and clinical issues, with reference to various recent recommendations of laboratory medicine and cardiology expert groups.