One-time low troponin level helps rule out MI

By Andrew M. Seaman

(Reuters Health) - A low plasma troponin I concentration can identify two-thirds of patients with very low risk of myocardial infarction who can be discharged from the emergency room, researchers said in The Lancet.

"The ultimate goal would be to have a single blood draw for the majority of patients," said study author Dr. Atul Anand, of the University of Edinburgh in Scotland.

In a derivation cohort of 4,870 people who came to emergency rooms in Scotland in 2013 and 2014 with symptoms of acute coronary syndromes, the researchers used a high-sensitivity troponin assay manufactured by Abbott Laboratories.

Ultimately, 3,799 of those people turned out not to have an MI. In those individuals, 61% had a troponin level below 5 ng/L.

That 5 ng/L cutoff, the researchers calculated, had a negative predictive value of 99.6% for an MI within the next 30 days.

Next, the researchers replicated their results in another 1,126 patients in Scotland and 308 patients in the U.S. In this cohort, the negative predictive value was 99.4%. And at one year, the risk of MI was 0.6% for patients with a troponin I level below 5 ng/L, vs 3.3% for patients with higher levels (adjusted hazard ratio 0.41; p<0.0001).

Patients who test below the 5 ng/L threshold are not in immediate danger, Dr. Anand said. They may be able to go home or be referred to their primary care doctor.

"The findings are pretty interesting and compelling," said Dr. Sripal Bangalore, a cardiologist at NYU Langone Medical Center in New York City.

However, the test is not perfect and some people who are having heart attacks will be missed, said Bangalore, who wasn't involved in the new study.

"There is a chance, but it's going to be an extremely small group of patients," he said. "But even if (the test is) accurate you have to do it in conjunction with additional follow-up."

Dr. Anand cautioned that the test was slightly less reliable when it was done within two hours of symptom onset.

The test costs about $8, and the researchers are in the process of completing a cost-benefit analysis.

Presently, the new test is available in Europe but not in the U.S.

The study was funded by the British Heart Foundation and Chief Scientist Office (Scotland).

SOURCE: http://bit.ly/1ht9Gzm and http://bit.ly/1ht9G2y

Lancet 2015.

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