Increased risk of gallstones after appendectomy: A longitudinal follow-up study using a national sample cohort.

To evaluate the association between appendectomy and the occurrence of gallstones using a national sample cohort from Korea.The Korean National Health Insurance Service-National Sample Cohort was collected from 2002 to 2013. We extracted data for patients who had undergone appendectomy (n = 14,955) and a 1:4 matched control group (n = 59,820) and then analyzed the occurrence of gallstones. The patients were matched according to age, sex, income, region of residence, hypertension, diabetes mellitus, and history of dyslipidemia. Appendectomies were identified using operation codes (Q2860-Q2863) for appendicitis alone (International Classification of Disease-10: K35). Gallstones were diagnosed if the corresponding International Classification of Disease-10 code (K80) was reported ≥2 times. Crude (simple) and adjusted hazard ratios (HRs) were analyzed using stratified Cox proportional hazard models, and 95% confidence intervals were calculated. Subgroup analyses were performed based on age, sex, and time period after appendectomy.The adjusted HR for gallstones was 1.78 (95% confidence interval = 1.51-2.09, P < .001) in the appendectomy group. Consistent HRs were found in the analyses of all the subgroups determined using age and sex, with the exception of men ≥60 years of age. The risk of gallstones was increased during the first year after appendectomy.The occurrence of gallstones was increased in the patients who had undergone appendectomy.