Urol Res (2010) 38:35–39 DOI 10.1007/s00240-009-0230-4 123 ORIGINAL PAPER Analysis of spontaneously passed urinary tract stones Daniel Muñoz-Velez · Fernando Garcia-Montes · Antonia Costa-Bauza · Felix Grases Received: 17 March 2008 / Accepted: 4 November 2009 / Published online: 1 December 2009  Springer-Verlag 2009 Abstract Most studies on epidemiology, composition, and recurrence of renal calculi include both spontaneously passed calculi and those retrieved after surgical manipula- tion or shock wave lithotripsy. The present study exclusively focused on epidemiology, composition, and recurrence of spontaneously expelled stones in patients from North and East Mallorca (Spain) which represents a geographically speciWc non-urban region of a developed country. The study involved 136 patients who spontane- ously passed 205 renal calculi. All calculi were classiWed and sub-classiWed according to composition after macro- scopic and microscopic examination. We also analyzed prevalence, gender, age, and stone recurrence rate over a period of 3 years. The peak incidence of spontaneously stone passage is within the fourth to sixth decade. Overall male to female ratio was 3/1. Calcium oxalate was the most prevalent composition (64.8%) followed by uric acid (25.3%), mixed stones (5.3%) and calcium phosphate cal- culi (4.3%). Uric acid stones were the most recurrent (50%) followed by calcium oxalate monohydrate papillary calculi (26.4%), calcium oxalate monohydrate un-attached calculi (19.2%), calcium oxalate dihydrate calculi (18.3%), cal- cium phosphate calculi (14%), and mixed calculi (12.5%). In conclusion, spontaneously passed stones in Mallorcan population have similar epidemiology, composition, and recurrence rate from that found in other developed countries. Calcium oxalate stones are largely the most spontaneously passed type of calculi and uric acid stones are the most fre- quently recurred. These Wndings are also found to be simi- lar to those reported in previous studies examining both spontaneously and non-spontaneously passed stones. Keywords Renal calculi · Spontaneously expelled stones · Recurrence · Epidemiology · Renal stone composition Introduction Most publications looking at epidemiology, composition, and recurrence of renal stones include both spontaneous passed stones and fragmented calculi retrieved by uretero- renoscopy, percutaneous nephrolithotomy, or shock wave lithotripsy [1–4]. There are no many studies speciWcally looking at spontaneously passed renal calculi [5, 6]. As expected, these studies show that stone passage rate is inversely related to increasing stone size. In one study look- ing at spontaneously passed stones 96.6% were sized ·10 mm and most of them (55%) were ·5 mm [6]. Another study showed that calculi exclusively composed by calcium oxalate (CaOx) were more likely to be sponta- neously expelled than calculi with any other composition [5]. They were followed by mixed CaOx and calcium phos- phate calculi. Many of the passed stones in this study weighted less than 0.10 g [5]. Our objective was to analyze epidemiology, composi- tion, and recurrence rates of spontaneously passed calculi in a population from North and East Mallorca (Spain). We speciWcally focused on spontaneously expelled calculi and the study of a geographically speciWc non-urban population in a developed country. D. Muñoz-Velez (&) · F. Garcia-Montes Department of Urology, University Hospital Son Dureta, C/Andrea Doria, 55, 07013 Palma de Mallorca, Spain e-mail: daniel.munoz@ssib.es; dmv2667@gmail.com A. Costa-Bauza · F. Grases Laboratory of Renal Lithiasis Research, University of Balearic Islands, Palma de Mallorca, Spain