But the researchers stressed that they have not yet confirmed a cause-and-effect link between higher white blood cell counts and illness risk. It remains unclear whether an elevated count helps trigger serious disease, or whether these cell counts rise naturally after illness.
And one expert said it's too early to make any changes to practice based on the findings.
"The findings are interesting and help to bolster that inflammation status is involved in the biology of many chronic diseases, but the findings do not suggest specific screening or treatment would be advisable," said Dr. Mary Cushman, director of the thrombosis and hemostasis program at the University of Vermont and Fletcher Allen Health Care in Colchester, Vt.
The findings are published in the May 8 issue of the Journal of the American College of Cardiology.
Generated by the bone marrow and spread throughout the body, white blood cells (WBC) -- also called leukocytes -- are the immune's system key weapon against infectious disease. In the absence of disease, they normally make up just one percent of a person's blood.
According to the U.S. National Institutes of Health, a simple blood test can easily determine whether a patient's WBC count falls within the normal range of 4,500 to 10,000 cells per microliter of blood.
While a below-normal WBC count may indicate bone marrow failure and/or liver and spleen disease, illness or invasion by a foreign body typically provokes a rise in white blood cells. Physical or emotional stress and certain chronic medications can also prompt an increase.
In their study, Ruggiero and colleagues examined data collected during a multi-decade study on aging. They tracked the medical histories of more than 2,800 men and women from the Baltimore and Washington, D.C., area.
Participants were healthy at the time of their entry into the study. WBC counts, body mass indexes, and cholesterol and blood pressure levels were tallied during biannual medical evaluations.
An analysis of death records revealed that those participants who died during the study period had higher WBC counts than those who survived through to 2002.
The finding applied to all patients regardless of their initial baseline WBC count, and held regardless of gender, age at death, or year of death. However, women tended to have significantly lower WBC levels than men.
Patients who had WBC counts between 3,500 and 6,000 cells per microliter of blood had the lowest observed rate of death, while those with readings above 10,000 had the highest death rate.
No firm conclusions were drawn regarding the risk for patients with WBC levels below 3,500.
However, the authors observed that death risk varied even within the normal WBC count range. Those with a high-normal WBC count of 6,000 to 10,000 had a 30 percent to 40 percent higher risk of death than patients with a low-normal WBC count of 3,500 to 6,000, the researchers said.
Ruggiero's team also calculated that for every additional 1,000 cells above the lowest end of the normal range (3,500), a patient's risk of death rose by just over 10 percent.
WBC counts, especially for a type of cell called neutrophils, rose progressively in the years before death, with significant bumps upward observed as early as five years prior to the end of a patient's life. In contrast, WBC counts remained relatively stable among people who survived.
People who died were also more likely to have smoked, to have been less physically active, and to have had worse cardiovascular health.
Death as a result of cardiovascular disease, especially, rose along with increasing WBC counts. WBC counts showed little connection to deaths by cancer.
Overall, white blood cell counts fell for both men and women over the nearly 45-year study period. A host of societal and lifestyle changes could explain the drop, the researchers said, including improvements in diet and exercise habits and the steady drop in smoking and drinking. Environmental changes, such as improved sanitary conditions and less frequent exposure to infectious agents, could also be factors.
The death rate for Americans has also fallen steadily over the past four decades, the authors noted. However, they stressed that they cannot establish any causal link between declines in white blood cell counts and improving life expectancy.
Measuring WBC might prove useful in predicting an individual's health risk, however.
"White blood cell count is usually measured in clinical settings as a marker of infection and hematological diseases," noted Ruggiero. "We suggest that differential WBC counts should be systematically screened and factored (into) the cardiovascular risk profile --and ultimately considered in clinical decisions concerning prescription of preventive interventions."
But Dr. James S. Goodwin, professor of geriatrics and director of the Sealy Center of Aging at the University of Texas Medical Branch in Galveston, isn't convinced.
"The good news is, that as this study shows, a rather substantial decline in WBC counts from around 1960 to 2000," he said. "It goes well with other research showing that there's been a general improvement in health over the last half of the 20th century in the Western world."
But Goodwin believes that, "from the perspective of the individual patient, this observational study suggests nothing specific that should be done differently. It is interesting from a scientific perspective. But for patients, it is not particularly important and has no clinical relevance."
Cushman agreed. "At issue is what the intervention should be if an elevated value is found," she said. "I don't believe that for WBC we know what to do, other than the things we should already be doing, like promoting a heart healthy lifestyle and appropriate screening and prevention for risk factors such as hypertension, diabetes, (and) smoking. This advice would not differ depending on whether the WBC was elevated."
More information
There's more on white blood cell counts at the U.S. National Institutes of Health. |
