Independent Association Demonstrated
White blood cell counts were measured at the beginning of the study, and women were divided into four levels . The first women with the lowest level of white blood cells and the fourth was comprised of women with the highest level. Medical histories were taken each year for six years of follow-up. Only participants who were entirely free of clinical CVD and cancer at the beginning of the study were included in the analysis.
Women in the fourth part (highest WBC) had a doubled risk for coronary heart disease death compared with women in the first quartile (lowest WBC), after statistical adjustment for other risk factors, the researchers found.
"Women in the upper quartile also had a 40 percent higher risk for nonfatal myocardial infarction (heart attack), a 46 percent higher risk for stroke, and 50 percent higher risk for total mortality," the authors write. "In multivariable models adjusting for C-reactive protein, the WBC (white blood cell) count was an independent predictor of coronary heart disease risk, comparable in magnitude to C-reactive protein (CRP)," they note.
"In summary, we have demonstrated that a WBC count in the upper quartile is independently associated with cardiovascular events and death in older women after adjustment for traditional risk factors," say the authors.
"These data add to available evidence in men suggesting a similar link and suggest that the predictive role of the WBC count is independent of CRP. Cardiovascular risk categorization by inflammatory markers, including the WBC count, may identify high-risk individuals who are not currently identified by traditional risk factors; further studies are needed to assess the effectiveness of risk reduction in these patients," the authors conclude.
Ripe Area for Investigation
"Several issues must be considered when interpreting data from observational studies on new risk factors," suggests Mary Cushman, M.D., M.Sc., of the University of Vermont, Colchester, Vermont, in an editorial accompanying this study. For leukocyte (white blood cell) count automated measurement methods are well standardized and precision excellent. There is little information on the variability of leukocyte count in individuals over time, but from limited data, the within person compared with between-person variability is similar to that of cholesterol or C-reactive protein (CRP)," she points out.
"Considering the use for vascular risk assessment in practice, the cost of leukocyte count determination is lower compared with other novel vascular risk markers under current consideration," Dr. Cushman writes. "One must also consider other costs of screening. There may be benefits or even harms and hidden costs," she notes.
"In addition, it is possible that assessment of more than one inflammation-sensitive factor at the same time allows better classification of patients as to whether they have inflammation," Dr. Cushman suggests.
"It is reassuring to see continuing study of simple and well-standardized biomarkers, such as leukocyte count, and risk of vascular outcomes. Whether novel risk markers, such as leukocyte count or CRP concentration, should be added to routine vascular risk assessment in asymptomatic patients is an area of ongoing intense interest," Dr. Cushman observes.
"Improvement of the precision of 'inflammation testing' by exploring even newer biomarkers or using combinations of tests is a ripe area for investigation. The latter will probably require pooled data from multiple studies to achieve precise risk estimates that can be translated into practice," Dr. Cushman concludes.
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