Stone recurrence among childhood kidney stone formers: results of a nationwide study in Iceland

Objectives: To examine the stone recurrence rate among childhood kidney stone formers in the Icelandic population. Materials and methods: We retrospectively examined kidney stone recurrence in a recently reported population-based sample of 190 individuals who experienced their first stone before 18 years of age in the period 1985–2013. Of these 190 individuals, 112 (59%) were females and the median (range) age at the incident stone diagnosis was 15.0 (0.2–17.9) years. Stone recurrence was defined as an acute symptomatic episode with imaging confirmation or self-reported stone passage, new stone detected by imaging in asymptomatic patients, and suspected clinical stone episode without verification. The Kaplan–Meier method was used to assess stone-free survival and the Chi-square, Fisher’s exact, Wilcoxon rank-sum and the log-rank tests to compare groups. Results: A total of 68 (35%) individuals experienced a second stone event, 1.7 (0.9–18.9) years after the initial diagnosis. The recurrence rate was 26%, 35%, 41% and 46% after 5, 10, 15 and 20 years of follow-up, respectively. The 5-year recurrence rate increased with time and was 9%, 24% and 37% in the periods 1985–1994, 1995–2004 and 2005–2013, respectively (P = 0.005). No difference in stone recurrence was observed between the sexes (P = 0.23). Conclusions: In our population-based sample of childhood kidney stone formers, the stone recurrence rate is similar to that reported for adults. The observed rise in stone recurrence with time may be related to closer patient follow-up in recent years or increased stone risk in general.