Determination of the kidney stone composition using infrared spectroscopy in Iran at a national referral center during 2019–2023

The national lifetime prevalence of urolithiasis is estimated at 6.6% in Iran. However, reports on the composition of kidney stones have been based on imprecise methods like the chemical analysis. No prior large-scale study has reported the composition of kidney stones based on the gold-standard methods (X-ray diffraction or infrared spectroscopy) in Iran. This study aimed to provide the composition of kidney stones based on Fourier transform infrared spectroscopy. This is a cross-sectional study assessing urinary stone composition from various cities in Iran at a referral center using infrared spectroscopy from February 2019 to March 2023. This study determined the stone composition of 1092 patients from 10 cities in Iran. Overall, the majority of stones were composed of calcium oxalate (n=498; 45.6%) and uric acid (UA, n=488; 44.7%) followed by cystine (n=49; 4.5%) and struvite (n=28; 2.6%). Stone composition in Shiraz and Isfahan was roughly similar with a higher percentage of UA stones (53.4% and 53.6%, respectively) while the capital city of Iran (Tehran) had less frequent UA stones (39.9%) with a higher percentage of calcium oxalate stones. The percentage of UA stones increased with age as it was 11.1% in children, 42.7% in adults, and 83.3% in geriatric patients (p<0.001). About 29.6% of cystine stones were observed in children. The most frequent stone composition among kidney stones in Iran was calcium oxalate and UA stones. This relative frequency of UA stones is considerably higher than many international reports from neighboring as well as distant countries. More cystine stones were observed in children and women. Geriatric patients' stones were mostly composed of UA.