In this week's issue of the New England Journal of Medicine, investigators from the U.K. report on the largest clinical trial yet conducted evaluating whether CRP (C-reactive protein) levels predict an increased risk of cardiovascular disease. In this study, CRP levels were measured at baseline in more than 7000 individuals who were subsequently followed in the Reykjavik Study. The CRP levels were then compared in individuals from this study who did and who did not have heart attacks or death from coronary artery disease during a 20-year follow-up period.
The investigators concluded that, while elevated CRP levels helped to predict the risk for cardiac events, the predictive value of the CRP measurements was relatively low. That is, knowing the CRP levels did not add much to risk measurement beyond knowing smoking status, whether obesity or hypertension were present, and cholesterol levels. If this were the case, recent recommendations that CRP levels ought to be routinely measured may need to be reconsidered.
Critics of this new study have already spoken up. Despite the fact that this new study is by far the largest CRP study ever conducted, they point out, several other studies have shown a very strong correlation between CRP levels and cardiac risk. Further, they note that the definition of "elevated CRP" in this new study is lower than that used in prior studies. In the study published this week, a CRP level of 2.0 mg/L was considered high - but the standard cut-off is 3.0 mg/L. If the higher value had been used in this study, they say, CRP would again have been shown to be a strong predictor of cardiac risk.
The bottom line: elevated CRP is indeed a predictive factor for cardiac disease. When and how often it should be measured, which value ought to be used to define "high" levels, and whether "official" recommendations should include the routine measurement of CRP will have to await the academic winnowing process, which is likely to take years. In the meantime, don't wait for the experts to count the number of angels that can dance on the head of a pin. Instead, act now. Stop smoking. Lose weight. Exercise. Get your blood pressure under control. Treat your elevated LDL cholesterol levels, and raise your HDL levels.
