A large new study casts doubt on one of the hottest ideas in the field of heart disease — that inflammation levels in the bloodstream are a powerful predictor of heart attacks.
The report in Thursday’s New England Journal of Medicine questions the value of a blood test already routinely used by some doctors to measure inflammation. And it challenges year-old recommendations from the U.S. government that doctors consider the test for some patients.
The researchers said their findings suggest that inflammation is only a moderate predictor of heart disease, less than some studies have indicated. They concluded that the test does not add much beyond other risk factors such as high cholesterol, high blood pressure and smoking.
“There’s no good scientific reason to be using it as a predictive test,” said Dr. John Danesh, one of the British researchers at the University of Cambridge.
But a key U.S. researcher in the field contends that the findings are not all that different from other studies that support the test, which he thinks should be used more widely, not curtailed.
“My concern is that even in the face of overwhelming evidence that this inexpensive blood test works, we are at risk of moving backward rather than forward,” said Dr. Paul Ridker of Harvard’s Brigham and Women’s Hospital in Boston.
Strong risk factor for heart disease?
Doctors can screen for low-level inflammation in the bloodstream by testing for C-reactive protein, or CRP, which fights infection. The painless inflammation can come from minor infections or irritations somewhere in the body.
At issue is whether high CRP alone is a strong risk factor for heart disease. The British researchers do not think so, while Ridker believes it is as important as high cholesterol and can spot people who have no other signs of heart disease.
In the latest research, Danesh and his colleagues used data from an Iceland study of heart disease that began in 1967. They compared 2,459 people who had a heart attack or died of heart disease over 20 years of follow-up with 3,969 participants who did not have a heart attack. Frozen blood samples were tested for CRP levels.
The researchers calculated that those with higher levels of CRP had a 45 percent increased risk of heart disease compared with those with the lowest levels. The researchers also analyzed 22 studies on the topic and found that patients with higher CRP levels had a 50 percent higher risk of heart disease.
That is far less than the early studies indicated. Eleven of the 22 studies analyzed were done before 2000, and together they showed a 100 percent increase in risk, or a doubling of the danger, the researchers said.
'A cautionary tale'
“It’s a cautionary tale about how high the bar really needs to be before we roll out scientific advances into the community and into the clinic,” Danesh said.
Dr. Thomas Pearson of the University of Rochester said the panel noted the weakness of the evidence and urged further study when it drew up the guidelines. He said the panel members were criticized as “way too conservative, stodgy and sticks-in-the-mud” by those who wanted more widespread testing.
“I think this is validating our conservatism,” he said.
The guidelines, issued last year by the Centers for Disease Control and Prevention and the American Heart Association, do not support testing for everyone. They give doctors the option of testing those judged to be at 10 percent to 20 percent risk of heart disease, based on such factors as age, high cholesterol and high blood pressure.
Since then, many doctors have begun routinely screening patients for CRP.
Ridker said the Iceland study used a lower CRP level than his studies to determine risk in the highest group, which could account for the lower findings.
He is now studying whether using cholesterol-lowering statin drugs to bring down CRP levels in patients is beneficial. Diet and exercise can also lower CRP.