Risk of immune thrombocytopenic purpura and autoimmune hemolytic anemia among 120 908 US veterans with hepatitis C virus infection

Background: There is emerging evidence that hepatitis C virus (HCV) infection play a role in the etiology of immune thrombocytopenia purpura (ITP) and autoimmune hemolytic anemia (AIHA), both of which are severe autoimmune cytopenias. Methods: To determine if HCV infection increases the risk for ITP and AIHA, we calculated the incidence rates of ITP and AIHA among 120 691 HCV-infected and 454 905 matched HCV-uninfected US veterans who received diagnoses during the period 1997 to 2004. After excluding individuals with a prior diagnosis of a lym-phoproliferative disease, human immunodeficiency virus, or cirrhosis, we fitted Cox proportional hazards models to estimate hazard ratios (HRs) and 95% confidence intervals (CIs) as measures of risks. Results: We found 296 ITP and 90 AIHA cases. Among HCV-infected vs HCV-uninfected persons, the overall in-cidence rates of ITP were 30.2 and 18.5 per 100 000 person-years, and for AIHA they were 11.4 and 5.0 per 100 000 person-years, respectively. Hepatitis C virus was associated with elevated risks for ITP (HR, 1.8; 95% CI, 1.4-2.3) and AIHA (HR, 2.8; 95% CI, 1.8-4.2). The ITP incidence was increased among both untreated and treated HCV-infected persons (HR, 1.7; 95%, CI, 1.3-2.2 and HR, 2.4; 95% CI, 1.5-3.7, respectively), whereas AIHA incidence was elevated only among treated HCV-infected persons (HR, 11.6; 95% CI, 7.0-19.3). Conclusions: Individuals infected with HCV are at an increased risk for ITP, whereas the development of AIHA seems to be associated with HCV treatment. It may be beneficial to test individuals newly diagnosed as having ITP for HCV infection.