October 3rd, 2012

What Is the Benefit of Adding CRP to Risk Factor Assessment?

In recent years, controversy has swirled around the role of inflammation in cardiovascular disease and the relative worth of measuring novel risk factors like C-reactive protein (CRP). Now, in a paper published in the New England Journal of Medicineresearchers from the Emerging Risk Factors Collaboration provide detailed calculations that estimate the benefits of adding inflammatory markers to risk factor models.

In an analysis containing nearly a quarter million people enrolled in 52 studies, the investigators examined the effect of adding CRP and fibrinogen to a model including age, sex, smoking status, blood pressure, history of diabetes, and total cholesterol. They concluded that the effect of adding CRP or fibrinogen to the model was roughly similar to the effect of adding HDL to the model. In a secondary analysis, they found that CRP and fibrinogen improved risk prediction in men but not in women and had more predictive power in smokers than in nonsmokers.

The authors conclude that “targeted assessment of CRP in people at immediate risk for a cardiovascular event could help to prevent one additional event over the course of 10 years for every 440 people so screened.” Here’s how they calculated this conclusion:

In a population of 100,000 adults 40 years of age or older, with an age profile similar to that in the European standard population and with age-specific and sex-specific incidences of cardiovascular events that are assumed to be the same as those observed in the current study… 15,025 persons would initially be classified as having a predicted risk of cardiovascular disease of 10% to less than 20% over a period of 10 years when the risk is calculated with conventional risk factors alone. … Assuming that allocation to statin treatment would be conducted according to the ATPIII guidelines (i.e., persons with a predicted risk of ≥20% and those with risk factors, such as diabetes, irrespective of their predicted 10-year risk), 13,199 participants at intermediate risk would currently not be eligible for statin treatment. Additional assessment of CRP in these 13,199 participants would reclassify 690 participants (5.2%) to a predicted risk of 20% or more, of whom approximately 151 would be expected to have a cardiovascular event within 10 years… Assuming that persons reclassified as being at a predicted risk of 20% or more would begin statin therapy, in accordance with the ATPIII criteria, such targeted assessment of CRP could help to prevent about 30 (i.e., 0.20 × 151) additional cardiovascular events over a period of 10 years…

Paul Ridker, a member of the Emerging Risk Factors Collaboration, shares his take on the findings with CardioExchange.  Read his analysis, and share your comments or questions, here.

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