The blood test to determine whether a patient has had a heart attack is flawed, with one in 20 patients registering levels of the protein troponin greater than the upper limit leading to potential misdiagnosis.
Of 20,000 consecutive patients undergoing blood tests at University Hospital Southampton, 5 per cent had levels of troponin (a protein released into the bloodstream during a heart attack) greater than the test manufacturer’s recommended upper limit.
But in most of these patients were being seen for other conditions and so there were no clinical signs or symptoms of a heart attack.
Troponin levels also differed according to several factors such as age, sex and whether inpatient or outpatient.
The researchers, led by cardiologist Professor Nick Curzen, say these results highlight the need for medical staff to interpret troponin levels carefully in order to avoid misdiagnosis of a heart attack and inappropriate treatment.
Current guidelines recommend troponin tests to help exclude or diagnose a heart attack. Manufacturers of troponin tests provide a recommended level (known as the 99th centile) based on values from a few hundred healthy individuals. This 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 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 per cent (10,580) were women.
Prof Sir Nilesh Samani, medical director at the British Heart Foundation, said: “Currently, troponin measurements are used in patients suspected of having a heart attack because troponin is released from the heart when it is damaged. However, the heart can release troponin when a patient is ill from other conditions not necessarily due to a heart attack. As this study emphasises, a positive test should not always be interpreted as being due to a heart attack, and other information should be taken into account.”