Current issues of ACP Journal Club are published in Annals of Internal Medicine


Diagnosis

Bedside serum cardiac troponin T analysis was sensitive for myocardial infarction

ACP J Club. 1995 Nov-Dec;123:72. doi:10.7326/ACPJC-1995-123-3-072


Source Citation

Antman EM, Grudzien C, Sacks DB. Evaluation of a rapid bedside assay for detection of serum cardiac troponin T. JAMA. 1995 Apr 26;273: 1279-82.


Abstract

Objective

To determine the test characteristics of a rapid, qualitative bedside immunoassay for cardiac-specific troponin T (cTnT) to diagnose myocardial infarction in patients admitted to the coronary care unit with chest pain.

Design

Blinded comparison of cTnT with clinical data and creatine kinase (CK) and creatine kinase-MB (CK-MB).

Setting

Coronary care and telemetry units of a U.S. tertiary care university medical center.

Patients

533 patients presenting to the hospital with chest pain suggestive of myocardial infarction were screened; 100 were included. Inclusion criteria were sufficient blood drawn at admission and adequate laboratory and electrocardiographic (ECG) results to establish a diagnosis of myocardial infarction.

Description of Test and Diagnostic Standard

Blood was taken and analyzed at admission and 8 and 16 hours later. cTnT was measured using a hand-held device containing specific monoclonal antibodies and was read by an experienced clinical chemistry technologist blinded to the other test results. Diagnosis of myocardial infarction was based on clinical evaluation, ECG readings, CK and CK-MB quantitative assays, and autopsy results by a blinded observer.

Main Outcome Measures

Test results were reported on the basis of time from onset of chest pain. Outcome measures were sensitivity, specificity, and likelihood ratios (LR) for myocardial infarction and the relative risk (RR) for development of serious cardiac events (death and nonfatal myocardial infarction).

Main Results

34 patients had myocardial infarction, and 28 patients subsequently died. At 4 time periods (0 to 2 h, > 2 to 4 h, > 4 to 8 h, and > 8 h), the sensitivity and specificity for cTnT were 33% and 95%, 50% and 100%, 75% and 100%, and 86% and 86%, respectively. At 0 to 2 hours, the likelihood ratio for myocardial infarction for a positive test result was 6.3 and the likelihood ratio for a negative test result was 0.8. At > 8 hours, the likelihood ratio for a positive test result was 6.0 and the likelihood ratio for a negative test result was 0.15. The RR for death and nonfatal myocardial infarction was 4.5 for a positive cTnT result on admission and 3.2 for patients with a CK-MB reading of > 6 ng/mL.

Conclusion

A rapid, qualitative bedside immunoassay for cardiac-specific troponin T was sensitive for the diagnosis of myocardial infarction in patients presenting to the hospital with chest pain.

Source of funding: Boehringer Mannheim (reagents and equipment).

For article reprint: Dr. E.M. Antman, Cardiovascular Division, Department of Medicine, Brigham and Women's Hospital, 75 Francis Street, Boston, MA 02115, USA. FAX 617-732-7134.


Commentary

The study by Antman and colleagues brings the rapidly expanding use of bedside (or "point-of-care") testing to diagnosis of myocardial infarction in patients presenting to the emergency department with chest pain. The authors show that the bedside assay for cTnT compares favorably with the diagnostic standard (a combination of clinical evaluation, electrocardiography, and CK and CK-MB) for diagnosing myocardial infarction. As the authors point out, however, sensitivity and specificity calculations must be interpreted cautiously because in certain instances, the new assay may be more sensitive or more specific (or both) than the current diagnostic standard.

The authors appropriately acknowledge the limited scope of the study, in that few patients with relatively circumscribed diagnoses and a relatively high risk were evaluated. This study did not compare the bedside assay with the quantitative laboratory assay for cTnT, nor were data gathered on other markers currently being evaluated, including cardiac troponin I, myoglobin, myosin components, and isoforms of CK-MB, all of which have promise as early or definitive markers (1). Evaluation is ongoing, and the clinical role of the bedside cTnT and other studies still needs to be defined for practice.

When fully evaluated, this and similar technologies are likely to further shorten the disposition of low-risk patients and speed the time to definitive therapy in high-risk patients with chest pain seen in the emergency department.

Steven Borzak, MD
Henry Ford Hospital Detroit, Michigan, USA