A new, highly-sensitive troponin I assay may prove to be more effective than a conventional troponin I assay at ruling in a diagnosis of myocardial infarction within 3 hours after admission to the emergency department, according to a report published in the Dec. 28 issue of JAMA.
Changes in the results of the highly-sensitive assay between admission and 3 hours ruled in the diagnosis of MI with a positive predictive value of 83% compared with the 58% PPV of the conventional troponin assay, said Dr. Till Keller of the University Heart Center Hamburg (Germany) and associates (JAMA 2011;306:2684-93).
The researchers noted that the results need to be independently validated.
The study compared the performance of the new, highly-sensitive assay (ArchitectSTATHigh Sensitive Troponin, Abbott Diagnostics) with that of one currently in clinical use (Architect STAT troponin-I assay, Abbott Diagnostics) in a study of 1,818 adults who presented consecutively to three German chest pain units with suspected acute coronary syndromes during a 2-year period. A total of 413 of these subjects (23%) received a final discharge diagnosis of MI.
Blood for the troponin I assays and assays for 10 other biomarkers was drawn at admission, and 3 hours later, and ECGs were performed at the same intervals.
For ruling out MI, the highly sensitive troponin I assay taken at admission (with the diagnostic cutoff value at the 99th percentile of 30 pg/mL) had a sensitivity of 82% and a negative predictive value of 95%. At 3 hours after admission, this assay had a sensitivity of 98% and a negative predictive value of 99%. The results for the conventional troponin I assay were comparable at admission and at 3 hours, the investigators said.
For ruling in MI, changes in the results of the highly sensitive troponin I assay were instructive. There were 951 patients with levels that were well below the 99th percentile at admission that increased above this cutoff point within 3 hours. This change, combined with a positive troponin level after 3 hours, had a positive predictive value of 83% – considerably greater than the 58% PPV for similar results on the conventional troponin assay.
A further analysis showed that the optimized relative change for the highly sensitive assay was a cutoff of 266%. "Using such a change of 266% in combination with the 99th percentile cutoff on admission, the specificity and the positive predictive value of [the highly sensitive assay] increased to over 99% and nearly 96%, respectively," Dr. Keller and colleagues said.
The assay was even more accurate at both ruling out and ruling in MI in the subgroup of 1,176 patients who had ST-elevation or clearly elevated troponin levels at admission. The highest negative predictive value to rule out MI, over 99%, was attained in these patients, as was the highest PPV, over 96%, to rule in MI.
This study was funded by the Johannes Gutenberg-University of Mainz, Brahms AG and Abbott Diagnostics. Dr. Keller and several of his associates reported grant support from Brahms AG and Abbott Diagnostics.