MONDAY, Nov. 28, 2005 (HealthDay News) -- C-reactive protein, a marker of inflammation, is a useful warning sign of stroke and other cardiovascular problems.
Or maybe it's not.
Two reports in the Nov. 28 issue of the Archives of Internal Medicine deliver apparently conflicting assessments about the value of testing people for C-reactive protein (CRP) when assessing their risk of stroke and heart disease.
One report, from the classic Framingham Heart Study, said that "elevated CRP level provided no further prognostic information beyond traditional office risk factor assessment to predict future major cardiovascular disease."
The other report, from a different study, found an increased risk of stroke associated with elevated levels of CRP and another molecular marker of inflammation, Lp-PLA2. Readings of those molecules "may be complementary beyond traditional risk factors in identifying middle-aged individuals at an increased risk for ischemic stroke," the kind caused by blockage of an artery, the researchers said.
But what seems to be a conflict really isn't, said Dr. Christie M. Ballantyne, lead author of the stroke report. He is director of the Center for Cardiovascular Disease Prevention at the Baylor College of Medicine, in Houston.
First, the two reports are talking about slightly different things, Ballantyne said -- the risk of stroke vs. the risk of all cardiovascular problems, including heart attacks.
And second, while information about CRP levels may not be very useful in most cases, they can be very helpful when readings of the standard risk factors -- cholesterol, blood pressure, family history and the like -- leave the doctor undecided.
"If you have borderline patients where you are not certain what to do, that's where these tests might be important," Ballantyne said.
He wouldn't run a CRP test on a healthy 25-year-old with no major risk factors, or on an older person with diabetes and high blood pressure, Ballantyne said. In both cases, the risk (or lack of it) is evident.
"But in some situations where you are not certain what to do, you are in a gray zone, it might be a useful test for that subset of patients," he said.
Dr. Philip Greenland, a professor of preventive medicine at Northwestern University's Feinberg School of Medicine, and editor of the Archives of Internal Medicine, agreed with that assessment. He also agreed with Ballantyne that what is true of CRP holds for other risk factors, up to and including what is regarded as the mightiest of them all, cholesterol levels.
"If you go through all the risk factors, such as age, gender, smoking, blood pressure, each time you enter a variable you get less and less impact," Ballantyne said. "If you add cholesterol last, it doesn't show anything significant. So, does that mean that cholesterol isn't important?"
Of course it's important, Greenland said, particularly because it is a major target of preventive therapy (which CRP isn't). But what happens with all these test results is that a change that might seem dramatic to an outsider -- doubling a risk, for instance -- may not be clinically important.
"Maybe you're talking about going from 1 percent risk to 2 percent risk, or from 5 percent to 10 percent," Greenland said. "That may not be enough of a shift to make a difference about what the doctor will do. It could matter only when you have a borderline case, because doubling the risk might take you over the line."
And there's a broader meaning, he said: "Many tests that we regard as useful by and large should only be applied in borderline cases."
Ballantyne added: "You don't end up using all these tests routinely on all patients. And unfortunately these tests are not used by physicians as much as they should be."
More information
You can learn more about C-reactive protein from the American Heart Association.
