Getting suspected heart attack patients to spit into a tube could help diagnose them six times faster than blood tests currently used.
Scientists have managed to process saliva in a way that allows standard testing kits to pick up on tell-tale signs of the deadly event in just 10 minutes.
In contrast, blood tests that look for the same chemical — called troponin — take at least an hour to achieve the same result.
Researchers in Israel said the first trials of the method showed it was 84 per cent as accurate as the commonly-used blood test.
Troponin is a protein that helps to regulate the heart’s function and is dumped into the bloodstream when someone’s heart is damaged during a heart attack.
Finding it in the blood is how doctors can tell for certain if someone’s symptoms are actually down to a heart attack. Not everyone has obvious symptoms, and the typical chest pain, light-headedness and breathlessness can be caused by other illnesses.
Heart attacks lead to more than 200,000 hospital visits every year in the UK and there are more than 1.4million living survivors. In the US some 805,000 people have a heart attack each year.
They happen when the blood supply to part of the heart is cut off and a bit of the muscle is starved of oxygen, which can kill or permanently damage it.
The heart does not generally stop completely when someone suffers an attack — that is called a cardiac arrest, which is much deadlier.
To test whether someone has had a heart attack, doctors test their blood to look for the protein troponin.
They also consider their symptoms and carry out an electrocardiogram (ECG) to check the heart’s activity.
If troponin is in circulating blood it usually means someone has had a heart attack because the protein is released into the body when the heart is damaged.
It is vital to diagnose a heart attack quickly because finding out how severe it is can dictate what treatment someone needs.
The current test to find troponin can take more than an hour, so scientists at the Soroka University Medical Centre in Be’er Shiva, Israel, wanted to find a faster way.
‘There is a great need for a simple and rapid troponin test for patients with chest pain in the pre-hospital setting,’ said Dr Roi Westreich.
Dr Westreich and colleagues processed and tested the saliva of people who had had heart attacks – and people who hadn’t – to see if they could spot troponin.
They found the saliva test accurately diagnosed 84 per cent of 32 people (27) who had been diagnosed through the gold standard blood test.
And the best thing about the saliva test was that it only took 10 minutes to produce the result, which was at least six times faster than the blood test.
The same testing kit that is used for blood could be used on the saliva, they found, as long as the spit sample had been processed first to remove other proteins that could confuse the test.
If the saliva wasn’t processed first, the test could only correctly diagnose six per cent of the heart attack patients (two out of 32).
Of 12 healthy patients, none were falsely diagnosed with heart attacks, showing that the test did not see troponin when it wasn’t present, which is vital to ensure people aren’t given treatment or surgery they don’t need. Blood thinners, for example, can cause excessive bleeding or bruising so should not be given unnecessarily.
It is not clear how long before the tests the troponin-positive patients had had their heart attacks.
Dr Westreich said: ‘Since no test has been developed for use on saliva, we had to use commercially available tests intended for whole blood, plasma, or serum, and adjust them for saliva examination.’
He added: ‘This early work shows the presence of cardiac troponin in the saliva of patients with myocardial injury.
‘Further research is needed to determine how long troponin stays in the saliva after a heart attack.
‘In addition, we need to know how many patients would erroneously be diagnosed with heart attack and how many cases would be missed.’
The British Heart Foundation said the study was promising but there were still doubts about the accuracy of saliva testing.
Its associate medical director, Professor Metin Avkiran said: ‘Measuring troponin in the blood provides the gold standard for diagnosing a heart attack and this small study adds to previous research that measuring troponin in saliva could be a less invasive and faster alternative.
‘However, more work is needed to further develop such tests and determine if they are as reliable as the current blood tests.’
Dr Westreich and his colleagues presented their research at the European Society of Cardiology Congress today.
It will later be published in a paper titled ‘Development of saliva-based cTnl point-of-care test: a feasibility study’.