• alpha-interferon;
  • epidemiology;
  • health care claims;
  • hepatitis C;
  • Medicaid;
  • treatment

Summary.  We aimed to determine rates of treatment with alpha-interferon medication in patients diagnosed with hepatitis C virus (HCV), to ascertain the prevalence of selected conditions that could influence initiation of interferon treatment, and to examine the association between the presence of these conditions and interferon treatment. A nested case–control design was used in California Medicaid (Medi-Cal) claims data covering the period from 1 January 1996 to 30 June 2002. Interferon-treated cases and non-treated controls were selected in a 1 : 2 ratio that matched the length of the observation period and year of index HCV diagnosis. Predictor variables examined in bivariate and multivariate analyses included demographics, substance abuse and dependence, psychotropic drug use, selected chronic conditions and medical utilization. The proportion of eligible subjects diagnosed with HCV and treated with interferon ranged from 10.7 to 13.9%. There were 529 treated cases that met the eligibility criteria and 1058 non-treated HCV patients selected as controls. Multivariate factors that increased the likelihood of treatment were a liver biopsy, a diagnosis of mild liver disease, a diagnosis of psoriasis, antidepressant use and classification of race/ethnicity as ‘other’. A decreased likelihood of treatment was linked to age ≥65 years, a diagnosis of kidney disease, one to four emergency visits and five or more emergency visits. The proportion of patients receiving interferon treatment in the Medi-Cal-insured population was low compared with published rates in HCV patients in other general medical settings. The diverse factors linked to initiation of HCV therapy raise compelling questions for further research.