Effect of family history on the risk of varicose veins is affected by differential misclassification

ObjectiveWe assessed differential misclassification in self-reported family history of varicose veins by comparing consistency of subject's own varicose vein status and the consistency of information on varicose veins in family members.Study Design and SettingA population-based cohort study of 4,903 middle-aged residents of the city of Tampere, Finland. A questionnaire was used at entry and at the end of the 5-year follow-up.ResultsThe estimated prevalence of positive family history of varicose veins varied depending on subject's own varicose veins from odds ratio (OR) 0.14 (95% confidence interval CI] = 0.01–0.58), in those with varicose veins reported in the first but not the second survey to OR 6.0 (95% CI = 2.0–47.8), in those with varicose veins reported in the second survey but not in the first. The incidence of varicose veins varied from 0.4 (95% CI = 0.1–1.4) to 4.1 (95% CI = 2.1–7.1) (per 100 person-years) depending how the proband memorized the family history.ConclusionResults on the effect of family history on varicose veins are subject to bias, which reduces the credibility of the reports proposing a strong hereditary component of varicose veins.