- Identification of factors predicting response to therapy is critical in the management of hepatitis C. This study assessed significance of lymphocytosis as a predictor of sustained virological response (SVR). Retrospective analysis of lymphocytosis and its correlation with virologic response was performed in 110 subjects with chronic HCV infection, who underwent interferon based therapy. Lymphocytosis was defined as ratio of lymphocytes to neutrophils (L/N) above 0.6. L/N ratios were calculated to avoid the impact of hypersplenism and constitutional leukopenia seen in African Americans (AA). At baseline, L/N of HCV subjects (0.86) as compared to Hepatitis B controls (0.56) was significantly higher (P < 0.01). More AA HCV subjects (81.8%) had lymphocytosis at baseline when compared to Caucasian Americans subjects with HCV (37.9%) or AA controls (39.4%). Nonresponders had a higher frequency of lymphocytosis at baseline compared to subjects that achieved SVR (61.4% vs. 36.0%, p<0.05). More HCV subjects without lymphocytosis at baseline achieved SVR (33.3%) compared to HCV subjects with lymphocytosis (15%). At week 12 of therapy, nonresponders had higher L/N (1.02 vs. 0.86) and frequency of lymphocytosis (73% vs. 48%) compared to subjects that achieved SVR (p<0.05 for both). Only 17.2% of subjects with lymphocytosis at 12 weeks achieved SVR compared to 37.5% without lymphocytosis (p < 0.05). All responders exhibited significant normalization of lymphocytosis after treatment. HCV induces lymphocytosis, especially in AA, and is associated with lower rate of SVR. Furthermore, lymphocytosis may serve as an inexpensive pre-treatment tool to predict poor virologic response to HCV therapy.