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

Abstract

Objective We 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 Setting A 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. Results The 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. Conclusion Results 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.