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Troponin I assay improved detection of MI in patients with suspected ACS
Mills N. JAMA. 2011;305:1210-1216.
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In a patient population with suspected acute coronary syndrome, a sensitive troponin I assay was able to increase the prognosis of MI and further identified patients at high risk for death and MI.
Researchers from Edinburgh, Scotland, performed this study using a sensitive troponin I assay (Abbott Architect assays, Abbott Laboratories) to detect cardiac injury in patients with suspected ACS who were admitted to the Royal Infirmary of Edinburgh.
The study was split into two phases: validation (n=1,038), or before lowering the threshold of detection of myocardial necrosis from 0.2 to 0.05 ng/mL with the assay; and implementation (n=1,054), or after lowering the threshold. The patients were then stratified into three groups based on myocardial necrosis concentration: less than 0.05 ng/mL (n=1,340); 0.05 to 0.19 ng/mL (n=170); and at least 0.2 ng/mL (n=582).
During the validation phase, event-free survival, which incorporated rates of recurrent MI and death, at 1 year was worse in patients with plasma troponin levels from 0.05 to 0.19 ng/mL, resulting in a death and MI rate of 39% vs. 7% in those with troponin assay concentrations of less than 0.05 ng/mL (P<.001) and 24% in those with concentrations of 0.2 ng/mL or more (P=.007).
However, lowering the diagnostic threshold to 0.05 ng/mL in patients with troponin concentrations of 0.05 to 0.19 ng/mL correlated with a reduced risk of mortality and recurrent MI from 39% to 21% (P=.01).
“In patients presenting with suspected ACS, the use of a sensitive troponin I assay increased the detection of MI by 29% and identified patients who were at the highest risk of recurrent MI and death,” the researchers wrote, later adding that the percentage “may increase further with future improvements in assay performance allowing the 99th percentile to be used as the diagnostic threshold. This greater diagnostic performance will have implications for public health targets, government statistics, health care resources, and on the employment prospects and insurance policies of our patients.” – by Brian Ellis
Clinicians have been reluctant to use the proper cutoff values with sensitive assays because they more often see elevations that are difficult to explain. However, when they do, they realize that they have been missing large numbers of patients who do poorly if not treated, but benefit substantially from appropriate therapy.
However, in this study, the 10% CV value was used. This was still a big jump from the prior standard, but it would be of interest to see if using the 99th percentile value of 0.012 ng/mL would have identified still more patients at risk. It is this value that we [in the joint task force] advocate using in the definition of acute MI, something that is misstated by the authors. The fact that the group with values <0.05 ng/mL had a much lower event rate does not exclude the likelihood that there was a group between the values of 0.012 and 0.05 ng/mL that was at risk and could also have been helped by more aggressive therapy. The authors mention this but do not provide any data about this group.
– Allan S. Jaffe, MD
Cardiology Today Editorial Board
Disclosure: Dr. Jaffe has acted as consultant for numerous companies that develop and manufacture blood tests.
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