Not. All. Troponin. Elevations. Are. Acute Coronary Syndrome.
This is just a simple, prospective, observtional study of 20,000 high-sensitivity troponin I results from a single hospital in the United Kingdom. All blood samples submitted to the lab were evaluated with a troponin assay, regardless of clinical indications or reasons for order. About half of included samples were outpatients, a quarter were Emergency Department patients, and the remainder were inpatients.
The manufacturer-stated upper limit of normal for the assay – Beckman Coulter Access AccuTnI+3, specifically – is 40 ng/L, with a coefficient of variation of less than 10% at that cut-off. Outpatients were the least likely to exceed this limit, at 2%, with an observed 99th percentile of 65 ng/L. In the Emergency Department, 6.1% exceeded the manufacturer-defined cut-off, with an observed 99th percentile of 215 ng/L. Finally, 7.3% of inpatients exceeded the manufacturer cut-off, with an observed 99th percentile of 563 ng/L.
The authors also tracked whether the patients had a troponin ordered by the clinical team, or had a final diagnosis of acute myocardial infarction, and perform some multivariate analyses with these patients excluded. Those only comprised 1,829 patients from this cohort, and excluding these patients made only small impacts upon their new “normal” 99th percentiles. Effectively, the point of this article is a reminder of the effect of concomitant illness on circulating troponin levels – and to take into account the likelihood of an ACS when interpreting troponin elevations above the manufacturer’s 99th percentile cut-off.
“True 99th centile of high sensitivity cardiac troponin for hospital patients: prospective, observational cohort study”
https://www.bmj.com/content/364/bmj.l729