Leukocytosis in obese individuals: possible link in patients with unexplained persistent neutrophilia.

BACKGROUND Recently, it was shown that fat tissue produces and releases inflammatory cytokines, and that obesity may be regarded as a state of low-grade inflammation. In this regard, we aimed to establish an association between obesity and persistent leukocytosis. PATIENTS AND METHODS We present clinical observations of obese subjects primarily referred for further evaluation of leukocytosis without a cause and validated the link between leukocytosis and elevated body mass index (BMI) in a cross-sectional study. RESULTS During 1999-2005, 327 patients were referred for further investigation because of persistent leukocytosis. Of these, 15.3% were asymptomatic obese, mostly females, with mild persistent neutrophilia accompanied by elevated acute-phase reactants. After careful evaluation, no recognized cause for leukocytosis was found other than the fact that the patients were obese. During a mean follow-up of 45.6 months, the leukocytosis and the elevated acute-phase reactants persisted and no new causes for leukocytosis were evident. Furthermore, in a cross-sectional analysis of 3716 non-smoker subjects, 62 were found to have leukocytosis. Compared with the population with a normal white blood count range, these subjects with leukocytosis had higher BMI, serum C-reactive protein (CRP) levels, waist circumference, and neutrophil and platelet count (all P < 0.0005). After logistic regression analysis, only BMI was shown to be associated with leukocytosis (P < 0.0005). CONCLUSIONS Obesity is recognized as a possible cause for reactive leukocytosis. Awareness of this 'obesity-associated leukocytosis' may help the clinician to avoid more extensive and unnecessary diagnostic work-up, particularly in similar obese subjects.