Blood test to diagnose heart attacks is flawed, warn researchers: One in 20 patients had test levels higher than recommended limit -- study results could help to avoid misdiagnosis and inappropriate treatment -- ScienceDailyThis recommended level is used as the upper limit of normal (ULN). In other words, if the value of troponin is above the 99th percentile, that is considered to be abnormal, and would indicate a heart attack in appropriate clinical circumstances. But little is known about the true distribution of the troponin level across a whole hospital population that includes inpatients, outpatients, patients undergoing surgery, in intensive care etc. So researchers measured levels of high sensitivity cardiac troponin I (hs-cTnI) in 20,000 inpatients and outpatients undergoing blood tests for any reason at University Hospital Southampton between 29 June and 24 August 2017. The average age of participants was 61 and 53% (10,580) were women. The researchers found that 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. One in 20 (1,080; 5.4%) of all 20,000 patients had a troponin level greater than 40 ng/L, but in most of these patients there was no clinical suspicion of a heart attack. Overall, 39% of all patients from the critical care units, 14% of all medical inpatients, and 6% of all patients from the emergency department had a troponin concentration greater than the recommended ULN.