NEW YORK (Reuter Health) – With the availability of more sensitive troponin I assays, lowering the diagnostic threshold for detection of myocardial necrosis from 0.20 to 0.05 ng/mL results in the detection of more MIs and more timely treatment, and consequently less morbidity and mortality, a Scottish team has shown.
In the March 23/30 issue of the Journal of the American Medical Association, Dr. Nicholas L. Mills, at the University of Edinburgh, and colleagues point out that lowering the cardiac troponin threshold is controversial, because of uncertainty “as to whether the benefits of small improvements in sensitivity will outweigh the problems that may arise as a result of reduced specificity.”
Furthermore, they add, “Whether lowering the threshold for detection of plasma troponin improves clinical outcomes in patients with suspected acute coronary syndrome (ACS) is unknown.”
To investigate these issues, the researchers conducted a two-phase study — validation and implementation — when a more sensitive troponin I assay became available.
Although the same troponin assay as used in both phases, only concentrations above the original diagnostic threshold (0.20 ng/mL) were reported to clinicians in the validation phase, while concentrations above the revised diagnostic threshold (0.05 ng/mL) were reported during the implementation phase, according to the report.
A total of 2092 patients with suspected ACS were studied. Whereas 28% had a troponin level of 0.20 ng/mL or higher, another 8% had troponin concentrations in the 0.05-0.19 ng/mL range, meaning that the lower diagnostic threshold resulted in a 29% increase in the rate of diagnosis of MI, the team reports.
As for outcomes, in the validation phase (when the 0.20 ng/mL threshold prompted treatment for MI), 39% of patients with troponin levels of 0.05-0.19 ng/mL had died or had a recurrent MI within 12 months compared with 24% of those with higher troponin levels.
In the implementation phase (when the 0.05 ng/ml cutoff prompted treatment for MI), the 12 month rates of death or recurrent MI were 21% in patients with troponin levels of 0.05-0.19 ng/mL compared with 24% in the group with higher levels.
In other words, lowering the diagnostic threshold for MI almost halved the rate of death or recurrent MI in the subgroup of patients with small increases in troponin below the previous diagnostic threshold.
Summing up, Dr. Mills and colleagues write: “The use of a sensitive troponin assay in patients with suspected ACS increased the rate of diagnosis of MI and identified a high-risk group of patients. Lowering the diagnostic threshold for MI was associated with an immediate and substantial improvement in the clinical management and outcome of patients with suspected ACS.”