Clot-busting drug doesn’t work for 1-in-4 patients – calls for aspirin resistance screening

  • Millions prescribed aspirin to combat blood clotting – but it doesn’t work for 25% of patients
  • Those who test positive at ‘significantly’ increased risk of heart attack and stroke
  • Countless lives could be saved by new £10 Urine test created by Randox to identify aspirin resistant patients

An aspirin a day may not necessarily keep the doctor away, especially if you are among the 1-in 4 people in Britain resistant to the beneficial effects of the ‘wonder drug.

A small dose of aspirin is taken by millions across Britain and around the world to thin the blood, in an attempt to reduce the risk of heart attack and stroke, but major clinical studies have shown that for 1-in-4 aspirin is ineffective. Validated research has also revealed that the risk of having a heart attack and indeed dying from a cardiovascular event is significantly higher in aspirin resistant patients.


One of the powerful effects of aspirin is that it inhibits the production of a blood clotting chemical called thromboxane, and as such, it is widely prescribed for the prevention of cardio vascular disease; however the blood thinning properties of aspirin do not work for everybody. In aspirin resistant patients, blood thinning is poor, therefore there is a greater likelihood of clots forming in arteries which are narrowed by fatty and fibrous plaques resulting in heart attack and stroke.

Responding to the problem, scientists at UK Biotechnology Company Randox have developed a new test for aspirin resistance, as Managing Director Dr Peter FitzGerald explains:

“We are faced with the fact that thousands of patients are at increased risk because they are not getting the benefits from their aspirin treatment. Some people have genetic resistance to aspirin, but high cholesterol, diabetes and pre-diabetes (affecting an estimated 1-in-3 people In England) may significantly contribute to the poor aspirin response. Aspirin effectiveness can also be reduced by non-steroidal anti-inflammatory drugs. To make sure these patients get the right treatment, we have developed a simple, £10 urine test, which can detect if a person is responding to their daily aspirin therapy.”

Dr Paul RJ Ames, Consultant in Haemostasis & Thrombosis at St George’s Hospital, London, who has been working with the new test, believes it could have a significant impact on the health of hundreds of thousands of patients in the UK and is calling for doctors to take aspirin resistance seriously: 

“Doctors need to realise that aspirin, the cornerstone of much cardiac therapy is not working for up to 25% of those taking it! Then there are the side effects such as ulcers to consider. Why should you continue to take something that actually isn’t doing any good?! It is also worrying that aspirin resistant patients are twice as likely to suffer a heart attack and almost four times more likely to suffer cardiovascular death than those who are responsive. This increased risk has been clinically validated in internationally recognised research and frontline care must take this knowledge into account. We need to begin testing for aspirin resistance, so that we can identify patients who need alternative treatments, ultimately reducing their risk of heart attack and stroke.”


A ‘meta-analysis’ (summary of 20 studies) published in the British Medical Journal, tracked almost 3000 patients with cardiovascular disease. They were tested and 28% (810 patients) were found to be aspirin resistant. The researchers discovered that 41% of the aspirin resistant patients had a CVD related event, 39.4% of them experienced Acute Coronary Syndrome and 5.7% died. The study concluded that aspirin resistant patients are at a much greater risk of serious cardiovascular disease compared to patients who are sensitive to aspirin.

Meanwhile a major Canadian research project which studied 976 aspirin treated patients, found that those who were aspirin resistant were twice as likely to have a heart attack, and worryingly, almost 4 times at greater risk of cardiovascular death. 

According to the British Heart Foundation, there are more than a quarter of a million heart attacks and strokes in the UK each year, it is not yet known how many of these were suffered by aspirin resistant patients, but it is evident that aspirin, the basis of treatment for millions at cardiovascular risk, is not a one-pill-wonder.

For the first time, a test is available which can rapidly and accurately identify aspirin resistance, a breakthrough in individual patient management; with the potential to revolutionise health care for those with cardiovascular risk.

Clinical Laboratory Survey