Gender and urinary pH affect melamine-associated kidney stone formation risk

OBJECTIVES: Melamine was known as a new risk for kidney stone due to recent incidences of milk powder contamination in China. Here, we performed a retrospective study to investigate whether age, gender, and urinary pH affect melamine-associated kidney stone risk. MATERIALS AND METHODS: A retrospective review was performed of 217 children aged less than 3 years old. All children had a history of being fed with Sanlu milk powder contaminated by melamine, and underwent a clinical screening on kidney stone in Shenyang from November 2008 to February 2009. A comparison with the Chi-square was conducted between 83 cases and 125 normal subjects. The difference between children's gender, age, and urinary pH was evaluated. RESULTS: A total of 208 subjects, 136 boys and 72 girls, were included in the study. Significant association was observed between melamine-associated kidney stone risk and gender [odds ratio (OR), 2.03; 95% confidence interval (CI), 1.11-3.74; P=0.02] and urinary pH (OR, 1.78; 95% CI, 1.01-3.11; P=0.04), respectively. Male children were at about twofold increased melamine-associated kidney stone risk compared with female children. Acidic urine showed about 1.78-fold increased melamine-associated kidney stone risk compared with normal urine. CONCLUSIONS: Our investigation results showed an association of gender and urinary pH with melamine-associated kidney stone formation risk.