• Michael J Sweeting, Daniela De Angelis, Keith R Neal, Mary E Ramsay, William L Irving, Mark Wright, Lisa Brant, Helen E Harris, Trent HCV Study Group, and HCV National Register Steering Group.
• MRC Biostatistics Unit, Institute of Public Health, Robinson Way, Cambridge CB2 2SR, United Kingdom. Michael.sweeting@mrc-bsu.cam.ac.uk
• J Clin Epidemiol. 2006 Feb 1;59(2):144-52.

ObjectivesTo estimate hepatitis C virus (HCV) progression rates between disease stages prior to cirrhosis, using data from liver biopsies in three observational cohorts. To demonstrate how the method of cohort recruitment can influence the estimation of HCV-progression rates.Study Design And SettingData came from three United Kingdom observational cohorts, assembled from different referral sources. In total, 987 HCV-infected patients with an estimated (or known) date of infection and at least one histologically scored liver biopsy were eligible for inclusion in the analysis. Liver biopsy scores were used to determine the stage of HCV-related liver disease. A three-state continuous time Markov model was used to estimate covariate-specific average probabilities of progression of disease.ResultsAfter adjusting for confounders, considerably different rates of disease progression were estimated in the three cohorts. For a group of patients with the same demographics, the estimated 20-year probability of progression to cirrhosis was 12% (95% confidence interval CI = 6-22) in a hospital-based cohort, 6% (95% CI = 3-13) in a posttransfusion cohort, and 23% (95% CI = 14-37) in a cohort recruited from a tertiary referral center.ConclusionResearchers using estimates of disease progression should be aware that the method of cohort recruitment has considerable influence on the progression rates that are derived.

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