Time changes in the spectrum of urinary stone composition: a role for climate variations?

BACKGROUND: An increase of the frequency of uric acid urinary stones compared to calcium-containing ones has been recently described. This study was aimed at assessing the frequency of different types of urinary stones in the population of northern Italy in the period 2016–18 compared to 2001–2003. METHODS: Analyses by infrared spectroscopy of 1007 stones endoscopically removed at two institutions in the area of Milan (Northern Italy) were retrospectively considered. Stones were classified as calcium oxalate monohydrate (COM) and dihydrate (COD), mixed uric acid/calcium oxalate (UC); uric acid (UA), struvite (ST); apatite (CAP); mixed calcium oxalate / apatite (CAPOX); others. The patients were divided into two groups: 2001–2003 and 2016–2018. The average temperature values of the region over the two time periods were obtained by the national statistical institute. RESULTS: The average age of the 2001–2003 group (45.8+/− 15.4 years) was significantly lower than the average age of the 2016–18 group (57.9+/− 14.8) (0.000). M / F ratio was similar in the two groups: 119 / 69 (1,0.58) in 2001–2003 and 527 / 292 (1,0.55) in 2016–18 (p = 0.862). COM stones tended to more frequent in 2016–18 group than in 2001–03. COD stones were significantly more frequent in 2001–03 than in 2016–18. ST stone frequency was increased from 2001 to 03 to 2016–18. No increase of uric acid containing stones was observed in 2016–18. Results were confirmed after adjustment by age. Averages annual regional temperatures increased from 14 °C to 15.4 °C during the two observation periods. CONCLUSIONS: No increase of UA stones was observed, probably due to the limited impact of the global warming in our temperate climate.