New Guidelines on CRP Testing

On January 28, 2003, the American Heart Association and the Centers for Disease Control released new recommendations for doctors on the testing of C-reactive protein (CRP) levels.

In recent years, evidence has been accumulating that increased levels of CRP in the bloodstream correlate with an elevated risk of cardiovascular events such as heart attacks and strokes. (CRP is thought to be a marker for inflammation.) In fact, in some circumstances elevated CRP levels are more predictive of cardiovascular events than elevated LDL cholesterol levels. (Click here for a recent article on CRP and what it means.)

However, there remains much confusion within the medical profession as to when it may be appropriate to measure CRP levels, and what to do about them when they are found to be elevated. This confusion stems from three major points: 1) It is not known whether the CRP levels themselves are causing a problem, or instead whether they are merely a marker for increased risk. 2) Therapy that clearly and reliably reduces CRP levels has yet to be identified. 3) It is not at all clear that reducing CRP levels reduce the risk of cardiovascular events.

What are the new recommendations?

The new recommendations from the AHA and CDC are an attempt to alleviate some of this confusion. The new recommendations are not offered as the definitive word on CRP, but merely as a statement of how to apply what we know so far to routine clinical practice. The AHA/CDC recommends measuring CRP levels in patients who - on the basis of multiple risk factor scoring with cholesterol levels, weight, level of exercise, smoking history, and presence of hypertension and diabetes - appear to have a moderately elevated risk of cardiovascular events. In these patients, an elevated CRP measurement would indicate that the risk may very well be much greater than "moderate." Such knowledge might spur both the doctor and the patient to adopt more aggressive risk-reducing measures.

For patients who are already known to have high risk, the recommendations continue, measuring CRP levels will not make anybody "smarter." The risk is high, whatever the CRP levels. Thus, given our current level of knowledge, in high-risk patients there is little to be gained by measuring CRP levels.

The AHA/CDC recommendations stop short of advising doctors to measure CRP levels in patients with a low risk of cardiovascular events. However, some investigators point out that in the Women's Health Study, women with elevated CRP levels had increased risk of heart attack and stroke even if their cholesterol levels were normal. Thus, a case can be made for measuring CRP in at least some patients with apparently normal risk.

What CRP levels are considered "normal"?

The AHA/CDC recommendations specify that "high-specificity CRP" (hs-CRP) levels should be measured. Since levels can fluctuate, they recommend that two separate CRP levels be measured, and then the two values averaged together. Levels less than 1 mg/L are considered "low," levels from 1 to 3 mg/L are considered "average," and levels greater than 3 mg/L are considered "high." High levels indicate an increased risk of cardiovascular events.