According to the report from Chinese Ministry of Health, there have been 6 deaths and 294 000 affected infants, more than 50 000 of them hospitalized, with urinary problems related to the consumption of melamine-contaminated powdered milk by the end of November 2008 . Simultaneously, because of the large potential health impact, free screen programs have been launched nationwide. To summarize the common features of melamine-associated urinary stones, we conducted this clinical investigation based on biochemical and ultrasonographic evidence.
A total of 1062 children fed with melamine-contaminated infant formula were screened for urinary stones. In all, 60 healthy children without melamine exposure were recruited as a control group. Chief complaints, complications and history of exposure to contaminated formula were documented. Ultrasonography of the urinary tract system was performed in all 1062 children. In patients and healthy children, urinalysis, renal function, liver status and serum electrolytes were determined.
We encountered 49 affected children from the 1062 screened ones, at a rate of 4.6% per ultrasound performed. The affected children ranged in age from 1 month to 96 moths, with a mean of 25 months. In all, 32 were male, and 17 were female. In 49 patients, 24 were fed with formula alone, and 25 were fed with formula in combination with breast milk. Duration of exposure was from 1.3 months to 84 months, with a mean of 19.5 months. The 6 formula brands were consumed by 49 affected children. The estimated melamine content in affected children was between 12 mg kg−1 and 2563 mg kg−1, with mean concentration of 1295.3 mg kg−1. Most affected children were asymptomatic and non-urinary findings. Patients exhibited lower urine pH and serum than those in healthy children, whereas for serum uric acid, alanine aminotransferase, aspartate aminotransferase and aninon gap, the opposite were observed. The stone diameter ranged from 2 mm to 18 mm with a median of 6.5 mm. Almost half of them had small stones <5 mm in diameter. Multiple stones were noted in all patients. Stones in bilateral and unilateral urinary tract were found in 11 (22.4%) and 38 cases (77.6%), respectively. Because none of our patients were in serious condition, simple conservative managements were adopted. One week later, stone diameters of 38 cases (77.6%) were significantly decreased. Among them, urinary stones were discharged completely in 21 affected children (42.9%).
The common features of urinary stones induced by melamine-tainted formula include the following respects. (i) Children from Chinese mainland exposed to higher content of melamine than ones from Hong Kong and Taiwan [2, 3]; (ii) Male infants who were younger than 3 years had more susceptibility than their opposites; (iii) Most of patients were asymptomatic, with sporadic urinary findings, metabolic acidosis, renal and liver disorders; (iv) Small (<5 mm in diameter) and multiple stones were noted in the majority of patients examined by ultrasonography; (v) Conservative therapy should be first tried in all patients without serious urinary obstruction and renal failure; (vi) The short-term outcome was satisfactory.