An inexpensive and routine blood test may help predict a person's risk of heart attack or heart-related death as reliably as more complicated tests, a new study suggests.

Researchers found that measuring the amount of white blood cells in the blood - and in particular measuring the ratio of different types of white blood cells -- was an accurate predictor of heart risk among a large group of people with heart disease. The researchers also say that this test is as accurate in predicting heart disease risk as other commonly used risk factors such as age, family history of heart disease, or C-reactive protein levels.

White blood cells are infection-fighting cells that may increase in response to infection or inflammation. Studies suggest that hardening of the arteries caused by cholesterol plaque -- atherosclerosis -- is linked to inflammation. Therefore, researchers suggest that measuring white blood cells may help reveal heart disease risk.

Researchers say if these results are confirmed by further studies, white blood cell counts may offer a new way to help doctors assess a person's heart disease risk and make treatment decisions.

"Perhaps in cases where patients' blood pressures or cholesterol levels are borderline, this test could tip the balance between treating some patients and not treating others," says researcher Jeffrey L. Anderson, MD, of the University of Utah in Salt Lake City, in a news release.

New Way to Spot Heart Attack Risk

Experts say the findings also lend more support to emerging evidence that inflammation and heart disease are closely related. For example, previous research has shown that elevated white blood cell counts are associated with heart disease risk, but it has been unclear what type of white blood cells carried this risk.

In the study, researchers compared white blood cell counts among a group of 3,227 patients who had not had heart attacks. But the patients had been referred for angiograms to measure clogged arteries after experiencing chest pain or other heart disease symptoms between 1994 and 2001.

After an average of three-and-a-half years of follow-up, researchers found that the risk of heart attack or death was higher among those who had higher white blood cell counts at the time of the angiogram.

But upon closer inspection, the results showed that certain subtypes of white blood cells were more predictive of heart attack risk than others. For example, patients with the highest levels of a type of white blood cell known as neutrophil had almost twice the risk as those with the lowest levels.

In addition, those with low levels of white blood cells called lymphocytes had only half the risk of heart attack or death.

Therefore, researchers found that the best predictor of heart disease risk came from comparing the ratio of neutrophils to lymphocytes. Patients with the highest ratios had more than double the risk of a heart attack or death compared with those with the lowest ratios.

The increased risk associated with white blood cells persisted even after taking into account other factors that might increase a person's risk of heart disease. White blood cell count is an independent predictor of heart attacks in patients with or at high risk of coronary artery disease, the researchers conclude.

"We are not sure exactly what role the white blood cells are playing, or whether it is good or bad; but the goal of this study was mainly just to show that they are predictive, and that this is a better predictive test, available at negligible extra cost, so why don't we make use of it?" says Anderson.

"With additional validation and testing in other populations, I believe that this ratio could be added to the other risk factors we know of, in order to build an even stronger risk profile that would allow people to make decisions about lifestyle changes or maybe whether they need to have additional diagnostic tests."

The results of the study appear in the May 17 issue of the Journal of the American College of Cardiology.

By Jennifer Warner, reviewed by Brunilda Nazario, MD

SOURCES: Horne, B. Journal of the American College of Cardiology, May 17, 2005; vol 45: pp 1638-1643. News release, American College of Cardiology.