A common cause of leukocytosis in elderly patients is bacteremia, according to the International Journal of Preventive Medicine. Bacteremia means that bacteria have invaded the bloodstream, according to MedicineNet. Bacteremia can result from chronic kidney failure, infections of the urinary tract, a potentially fatal complication of infection called sepsis, and other problems with the blood, including an abnormally high level of platelets. Elderly patients are also more likely to die because of these infections.
Elderly people, as well as people with compromised immune systems, are especially at risk for sepsis, claims Mayo Clinic.
Arthritis is another condition that causes a proliferation of white blood cells, says American Family Physician. Chronic lymphocytic leukemia can also cause leukocytosis in the elderly. People with chronic lymphocytic leukemia usually have a much less virulent version of leukocytosis than those with acute types of leukemia. Patients who are asymptomatic usually don't require urgent treatment.
Leukocytosis can also occur in people who have undergone total hip and knee replacement surgery, according to the National Center for Biotechnology Information. In some cases, two days after the surgery, patients' white blood cell counts increased to three times the normal levels, then fell to nearly normal by the fourth day after the surgery. This was especially pronounced in older patients.