C-Reactive Protein and Prediction of Risk for Cardiovascular Disease in Women

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The summary below is from the full report titled "The Effect of Including C-Reactive Protein in Cardiovascular Risk Prediction Models for Women." It is in the 4 July 2006 issue of Annals of Internal Medicine (volume 145, pages 21-29). The authors are N.R. Cook, J.E. Buring, and P.M. Ridker.

What is the problem and what is known about it so far?

C-reactive protein (CRP) is a blood protein that increases when inflammation is present. Inflammation is involved in the blockages in arteries that lead to cardiovascular disease, such as heart attacks and strokes. High CRP levels are associated with cardiovascular disease. However, just because CRP is associated with the risk for cardiovascular disease does not mean that CRP or inflammation causes cardiovascular disease or that treatments to reduce CRP levels will reduce cardiovascular disease.

Currently, doctors evaluate a patient's chances of developing cardiovascular disease by examining risk factors, such as cholesterol levels, diabetes, high blood pressure, smoking status, and age. Sometimes doctors use mathematical models to estimate the chance that a person will develop cardiovascular disease in the future. The Framingham risk model is a model that doctors commonly use. The model is useful, but not perfect. Some people who have no risk factors develop cardiovascular disease. Others who have multiple risk factors don't develop disease. Researchers wonder whether adding additional factors, such as CRP, to the Framingham model would improve the ability to estimate a person's chances of developing disease.

Why did the researchers do this particular study?

To compare cardiovascular risk predictions models that do and do not include CRP.

Who was studied?

15,048 women age 45 years and older who were free of cardiovascular disease, cancer, and diabetes at the start of the study.

How was the study done?

At the start of the study, the researchers collected information on cardiovascular risk factors, such as age, blood pressure, smoking status, and diabetes. They also collected blood samples to measure cholesterol and CRP levels. During follow-up, the researchers collected information about health outcomes, including cardiovascular disease. The researchers then compared the ability of models that did and did not include CRP to predict patients' chances of developing cardiovascular disease over the next 10 years.

What did the researchers find?

Age, smoking, and blood pressure were the most powerful predictors of cardiovascular disease. Adding CRP to the models improved the accuracy of estimates of who would develop disease. The improvement was mostly among women who had at least a 5% (5 in 100) chance of developing heart disease over the next 10 years. Among this group, adding CRP to the model improved prediction for 20% (20 in 100) of study women.

What were the limitations of the study?

This study included only women who were generally at low risk for cardiovascular disease. The results might not apply to men.

What are the implications of the study?

This study will inform discussions about the value of incorporating CRP levels into methods of evaluating the risk for cardiovascular disease. However, we do not yet know whether treatments to lower CRP levels reduce cardiovascular disease.