Urinary Excretion of Cyanuric Acid in Association with Urolithiasis: A Matched Case-Control Study in Shanghai Adults

Melamine (MEL) has raised human concern since the 2008 milk scandal. Co-exposure to MEL and one of its analogues, cyanuric acid (CYA), has been reported to have a synergistic effect on promoting urolithiasis. However, few epidemiological studies have reported urolithiasis in association with exposure to CYA based on our knowledge. We therefore conducted a case-control study to investigate whether cases of urolithiasis had higher excretion of urinary CYA than the controls. Spot urine samples from 70 adult cases and first-morning urine samples from 70 controls (matched by age and sex) were collected for the measurement of MEL, CYA, and other two analogues in urine. The case group also had 2.81-fold higher concentration of urinary CYA than the control group (34.87 versus 12.43 ng/mL, p-value < 0.001). Multivariate conditional logistic regression models adjusting potential confounders of personal characteristics identified the risk factor of urinary CYA as a continuous variable with odds ratio (OR) (95% confidence interval, 95%CI) of 1.11 (1.02–1.21) (p-value = 0.021) and having meals at restaurants with OR of 5.71 (1.01–32.31) (p-value = 0.049). Compared to the participants having the lowest quartile of CYA concentration in urine, participants at the second, third, and fourth quartile groups had ORs of 13.94, 83.69, and 118.65 with p-values of 0.004, <0.001, and <0.001, respectively. The high excretion of urinary CYA in urolithiasis cases might be the sign of stones in patients consisting of CYA, then proving the attribution of CYA exposure in the etiology of urolithiasis. These findings are important since CYA is a degraded by-product of chlorinated isocyanuric acid disinfectants, which are widely used in daily life not only in swimming pool water but also in other scenarios, such as serving as anti-pandemic disinfectants. Risk assessment of CYA serving as a by-product of disinfectants needs to be conducted in future studies.