DEAR DOCTOR K:
Both my parents had heart disease, so I’m worried I might get it. A friend said I should get a CRP test, but my doctor hasn’t ordered one. Should I ask him about the test?
The answer is controversial. For full transparency, I should say that this test was developed and studied by a colleague of mine at Harvard Medical School, and revenue from the test comes to my colleague and to the hospital where I practice.
The C-reactive protein (CRP) blood test measures inflammation in the body. What does that have to do with heart disease? We now know that many heart attacks and strokes occur because cholesterol-rich plaques of atherosclerosis rupture. When that happens, blood clots form that can cut off the blood supply to part of the heart or brain. Plaques rupture because of inflammation inside them.
Like most tests, the CRP test is valuable in some people, but not all. A valuable test is one that tells us there is value in taking some particular action: having an additional diagnostic test, taking a particular treatment or adopting a healthy lifestyle.
A study published in the New England Journal of Medicine in 2012 found that checking CRP levels may not be valuable in the average person. (And, unless you are from Lake Wobegon, there is a chance that you are an average person.) The review article looked at 52 studies that included 240,000 people. The researchers added the CRP results to standard risk factors, such as diabetes or high cholesterol. Using all of this information, they classified people by their risk of cardiovascular disease and whether they needed preventive treatment.
The researchers estimated that the CRP tests would have prevented only one heart attack or stroke for every 400 to 500 people screened. In other words, the CRP test added little information about cardiovascular disease risk in the average person, beyond what the standard risk factors already showed.
Several authoritative groups recommend that the test be performed in people who are at intermediate risk for heart disease based on other risk factors: high blood pressure (hypertension), smoking, high levels of LDL cholesterol, diabetes, or close relatives who have developed heart disease at a young age.
The logic in this recommendation is straightforward. If you are at high risk, according to these other risk factors, knowing your CRP level won’t change your doctor’s advice. I’m a good example. I am at higher risk than the average person my age for a heart attack, and my CRP level was normal. But if I had used that as an excuse not to follow a healthy lifestyle, I’d have been unwise.
And if you are at low risk, according to these other risk factors, finding that you have a high CRP level won’t lead to any additional testing or treatment that is likely to help protect you. But if you’re at intermediate risk, knowing your CRP level can be valuable.