What is the workup for persistent (months to years) elevation of the WBC count in an asymptomatic patient who demonstrates no other abnormalities in the complete blood count?
—Phuong Thi Ngoc, DO, Clermont, Fla.

It may be more common than realized for otherwise healthy patients to have an isolated elevated WBC count. The normal adult WBC count ranges from 4,400 to 11,000/µL. Elevation is considered to be >11,000 or a count that is two standard deviations above the mean. Therefore, more than 2.5% of adults will have WBC counts >11,000 under “normal” circumstances. Many of the causes of leukocytosis can be ascertained via a thorough history: Symptoms of active infection, recent stress, ongoing tobacco use, pregnancy, vigorous exercise, asplenia, and even medications have been implicated. If your patient’s history, exam, peripheral blood smear, and complete blood count are otherwise normal, then you can likely continue to follow along. Ward and Reinhard in 1971 reported on 34 healthy subjects with leukocytosis who had normal bone marrow aspirates and leukocyte alkaline phosphatase scores. The patients were followed for longer than 20 years without medical problems (Ann Intern Med. 1971;75:193-198). The overarching concern is to rule out myeloproliferative disease. Consider referral if the WBC count is >20,000 or blast forms are present on a smear.
—Christopher Ruser, MD (100-16)

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