Findings from a large clinical trial called the Women's Health Initiative (WHI) Observational Study recently demonstrated that for women over 50, the white blood cell (WBC) or leukocyte count could be just as important as C-reactive protein (CRP) in identifying their risk of having a stroke or a coronary event.

After studying 72,242 postmenopausal women ages 50 to 79 years who were initially free of cardiovascular disease (CVD) and cancer for approximately 6 years, the WHI researchers discovered that women with WBC counts in the highest quartile had a 40% higher risk of having a heart attack than women with WBC counts in the lowest quartile. WBC counts in the highest quartile were also associated with a 46% higher risk for stroke and a 50% higher risk for death.

These findings, in conjunction with a sub-study of 608 women that compared CRP and WBC counts in assessing this population for coronary heart disease (CHD) risk, prompted the researchers to remark that in women over 50, “the WBC count is an independent predictor of CHD risk, comparable in magnitude to C-reactive protein.” In fact, the sub-study findings showed that women with both a high CRP concentration and a high WBC count were nearly seven times more likely to develop CHD as compared to women who had low CRP and WBC counts.

Because the WBC count is a widely available, well-standardized, and inexpensive test, doctors could quickly embrace it as a new marker of CHD risk in women over 50. Before it can be used as screening test, though, there are several limitations that some medical professionals would like to see addressed. For example, patient results for WBC counts are given as the number of white blood cells per cubic millimeter; they are not reported in quartiles as required for this risk assessment. Moreover, there is no standardized definition that sets the threshold for the highest quartile for a WBC count; the upper quartile will vary by the population sampled. In addition, more studies are needed to determine how the WBC count can best be used in conjunction with CRP and other markers of CHD risk, including cholesterol and D-dimer.

Sources
Margolis, KL et al. Leukocyte Count as a Predictor of Cardiovascular Events and Mortality in Postmenopausal Women: The Women's Health Initiative Observational Study. Arch Intern Med. 2005;165:500-508. Abstract available online

Cushman, Mary. Leukocyte Count in Vascular Risk Prediction. Arch Intern Med. 2005;165:487-488.