Using a single cutoff of high sensitivity cardiac troponin I (hs-cTnl) to diagnose acute myocardial infarction is both flawed and inappropriate, warn British cardiologists.

While the test may be useful to rule out acute MI, the use of a single abnormal value to rule in acute MI would lead to widespread overinvestigation and overdiagnosis, they say.

Cardiologist Nick Curzon from University Hospital, Southampton, UK, and colleagues found that 1 in 20 patients had a hs-cTnl concentration greater than the manufacturers recommended upper limit of normal.

The study cohort of 20,000 consecutive inpatients and outpatients were undergoing a blood test for any reason and there was no clinical suspicion of acute myocardial infarction in most of the patients.

The 99th centile of troponin for the whole study population was 296 ng/L compared with the manufacturer’s recommended level of 40 ng/L, results showed.

In particular, the risk of potential misdiagnosis of acute MI was seen in emergency patients (215ng/L) and acute medical admissions (1459 ng/L).

The notion of using a single binary value greater than the supplied ULN of any assay to diagnose whether a patient has had an acute MI was flawed, the researchers said.

“It is important for frontline clinical staff to understand that using a single cutoff of hs-cTnl to diagnose acute myocardial infarction might be inappropriate and that the ULN  of the assay depends on the setting and the clinical characteristics of the patient,” they wrote in their study published in The BMJ.

“At present, using the 99th centile to help rule out a diagnosis of acute myocardial infarction is clear cut and is based on a “healthy” reference population. However, the recommended threshold and its application to patients presenting to hospital to rule in acute myocardial infarction is problematic, particularly when the degree of suspicion is low and other factors might contribute to the cardiac troponin concentration.”

“We would advocate that clinical staff are aware of the current guidelines for diagnosing acute myocardial infarction, which are not always adhered to, and also that they have a very clear indication for requesting the test,” they added.