Wednesday, April 2, 2014

The Troponin to End All Troponins

Yet again, the internet has exploded with magical thinking: “Simple test could help rule out heart attacks in the ER: study

What is this one “weird” trick that builds muscle, saves electricity, gives you a flat belly, and detects heart attacks in the Emergency Department?

It’s just another high-sensitivity troponin publication.

This is a two-year retrospective evaluation of patients presenting to two Emergency Departments in Sweden, culling the electronic health record for patients aged greater than 25 who were evaluated for chest pain and had at least one hs-cTnT level measured.  These patients were then followed through the central Swedish Health Registry for subsequent hospital admissions or death for 30, 180, and 365 days following their Emergency Department Visit.

Of this cohort, 8,883 had an initial hs-TnT <5 ng/L; within 30 days, 15 of these patients received the diagnosis of MI and two patients died.  Thus, a negative initial hs-TnT was associated with a 0.17% absolute risk for MI and a 0.023% risk of death from cardiovascular causes within 30 days.  Therefore, this test is magic.

Except, it isn’t.  We’ve known for almost two decades that negative biomarkers confer an excellent 30-day prognosis.  This is simply a more sensitive version of those prior assays, with the potential to pick up troponin elevations earlier in the time course of cardiac ischemia.  Earlier detection of cardiac ischemia then potentially enables a one-set rule-out, rather than a two-set or three-set traditional evaluation.

However, as is the natural order of things, when the balance of a test shifts to assign greater significance to a negative test result, the significance of a positive test results declines.  Patients admitted to the hospital with hs-TnT levels >14 ng/L received a diagnosis of MI only 30% of the time.  Their data tables are insufficient to estimate the specificity of the test at the cut-offs provided in the paper, but, clearly it is poor.

The authors promote this test as a tool to discharge greater numbers of patients from the Emergency Department.  However, any potential performance improvement will depend on the baseline admit rate at your institution.  Then, ultimately, we’ll need a more sophisticated approach to interpreting this test – moving beyond the dichotomous interpretation of “positive” and “negative” biomarkers, and describe the detectable levels on a continuum in the context of the concomitant disease processes – including, but not limited to, acute coronary syndrome.

“Undetectable High Sensitivity Cardiac Troponin T Level in the Emergency Department and Risk of Myocardial Infarction”

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