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  • Clinical medicine

Published online: 18 February 2009 | doi:10.1038/nchina.2009.29

Urology: Melamine matters

Felix Cheung

Introduction

© (2009) Elsevier

Last year, thousands of children in mainland China fell ill after consuming milk products that had been tainted with the chemical melamine. Diagnosis showed that these children suffered kidney problems and, in some serious cases, renal stones and renal failure. The perplexing thing, however, is that melamine by itself has low toxicity and is rapidly eliminated after ingestion, so it is unclear whether other contaminants may have played a role in causing the ill effects. Ching Wan Lam and Paul Kwong Hang Tam at the University of Hong Kong and co-workers¹ say they have found the mechanism by which these renal stones are formed in humans.

Children with a history of consuming melamine-tainted milk products were recruited to the study. Using ultrasonography, the researchers identified 15 children who had renal stones, with sizes ranging from 2.5 to 18 mm.

Melamine is known to form insoluble crystals with cyanuric acid, a structural analogue of melamine that often co-exists as an impurity or metabolite in the diet. The researchers collected urine samples from the children and analysed the levels of melamine, cyanuric acid and other risk factors.

They found that children with renal stones had much higher melamine levels in their urine than those without, and that there was a strong correlation between urinary melamine level and size of stone. The urine of children with renal stones was also found to be more acidic. On the contrary, there was little difference in levels of urinary cyanuric acid between the children.

According to investigations after the 2007 pet food recall in the USA, the combination of melamine and cyanuric acid was found to be the cause of acute renal failure in cats and dogs that had consumed melamine-tainted food. The new findings show that cyanuric acid might not be the cause of renal stones in humans. Acidity might play a role instead, which probably explains why renal stones discovered in the study (pictured) were of a softer consistency than those previously found.

Some clinicians have tried to acidify the urine in patients as a way to break up the renal stones. However, the researchers warn that this form of treatment might do more harm than good to the patients.

The authors of this work are from:
Department of Pathology, Surgery and Microbiology, Queen Mary Hospital, University of Hong Kong, Hong Kong, China; Clinical Immunology Center, Southern Medical University, Guangzhou, China; Department of Pediatrics and Ultrasound, Zhujiang Hospital, Southern Medical University, Guangzhou, China.

Reference

1. Lam, C. W. et al. Diagnosis and spectrum of melamine-related renal disease: Plausible mechanism of stone formation in humans. Clin. Chim. Acta doi:10.1016/j.cca.2008.12.035 (2009). | Article |