CRP Testing for Coronary Heart Disease
Edition: March 2003 - Vol 11 Number 03
Author: Laura Thill
It’s no passing fad. C-reactive protein (CRP) testing – which has gained widespread attention in recent months – is now recommended by the American Heart Association (AHA) and the Centers for Disease Control and Prevention (CDC) as an indicator for a risk of heart disease.
Using the test to determine a patient’s risk for heart disease is still a new concept. In fact, a waived test does not yet exist. Still, some distributors are noticing heightened interest in it.
CRP is an inflammatory marker found in the blood. Normally, a patient’s blood serum contains no CRP, according to the National Institutes of Health (NIH). Increased concentrations have been linked in the past to such diseases as type 2 diabetes, rheumatoid arthritis, rheumatic fever, cancer, tuberculosis and pneumonia. Now it’s accepted as an indicator of coronary heart disease as well. A well-publicized article last November in the New England Journal of Medicine brought CRP testing to the public’s awareness.
It’s not necessary to use this test to screen all adults, according to the AHA. And the test should not be considered a replacement for traditional cholesterol tests or high blood pressure screening. As one expert notes, if a patient tests positive for CRP, but has normal lipid levels, there’s no medicine that the physician can prescribe. But when the physician is unsure of what treatment approach to use for an intermediate-risk patient, CRP testing may help him or her decide, according to Thomas A. Pearson, M.D., Ph.D. (co-chair of the AHA/CDC writing group that developed the new recommendations).
“There’s no question about it,” says Jerry Phelan, chemistry specialist at LABSCO (Louisville, Ky.). “This is such an easy test. I imagine it will become as routine as a cholesterol test. We’ve been getting lots of calls about it.”
According to Phelan, Dade-Behring Inc. (Deerfield, Ill.) was one of the first manufacturers to develop the CRP test, along with the instrumentation required to perform it. Since then, other instrument and reagent manufacturers have followed suit. In fact, manufacturers of chemistry or immunoassay analyzers, which can also be used for CRP testing, are now tapping into the CRP market and providing the drug as well, notes Phelan. There’s no shortage of availability, he adds.
The test ranges in price from $20 to $40, depending on insurance considerations, according to Gary Sammuels, external communications, Quest Diagnostics (Teterboro, N.J.).
A simple blood test, CRP testing requires no preparation and is associated with only slight risks, according to the NIH. As with any blood test, there’s a minimal risk of excessive bleeding, fainting, hematoma or infection at the puncture site.
The recent study (New England Journal of Medicine, Nov. 14, 2002) measured baseline C-reactive protein and LDL cholesterol in 27,939 American women. The women – all of whom appeared healthy at the onset of the study – were followed for about eight years for signs of ischemic stroke, myocardial infarction, coronary revascularization and cardiovascular-related death.
Since C-reactive protein and LDL cholesterol measurements identify different high-risk groups, the researchers concluded that screening for both of these markers provides a more reliable indicator of heart disease than screening for one marker alone. At the same time, C-reactive protein levels proved to be a more accurate predictor of cardiovascular events than LDL cholesterol levels. The researchers found that subjects with high CRP levels were twice as likely as subjects with high cholesterol to die from heart attacks or stroke. In fact, half of the heart attacks recorded in the study occurred in women who reportedly had safe cholesterol levels.
So a high CRP level can alert a patient who has no apparent risk factors for heart disease. The patient, in turn, may be more apt to change his or her diet and exercise regime. According to Quest Diagnostics, there are two types of candidates suitable for CRP testing:
· Long-term risk. Asymptomatic people with – or without – a history of cardiovascular disease.
· Short-term risk. Patients admitted to a hospital with a suspected or known cardiovascular-related episode.
The AHA/CDC group has established some guidelines for reporting CRP test results with regard to cardiovascular heart disease:
· Results should be expressed as milligrams per Liter (mg/L).
· Concentrations less than 1.0 mg/L suggest a low risk.
· Concentrations between 1.0 mg/L and 3.0 mg/L suggest an average risk.
· Concentrations over 3.0 mg/L define a high-risk candidate.
High-risk individuals have double the risk for cardiovascular disease compared with low-risk testers.
The AHA/CDC group has established the following parameters for using the test:
· There’s no need to use the CRP test to screen the entire adult population.
· Elevated CRP levels can serve as an independent marker for high risk and may provide a means for evaluating moderate-risk patients.
· It has not yet been proven that CRP levels provide a reliable tool for determining treatment efficiency.
Experts agree that CRP tests will likely join the ranks of other high-sensitive diagnostic tests. As far as whether a rapid CRP test is in store remains to be seen.
“I suspect people are working [on developing] a rapid test,” says Phelan. “But, at this point [we] require a high-sensitivity CRP test for a cardiac marker, as well as regular instrumentation to run the test. Rapid tests aren’t sensitive enough.”