Children exposed to low doses of melamine did not develop severe kidney problems, researchers in Hong Kong say.

For the study in this week's issue of the British Medical Journal, doctors examined 3,170 children aged 12 or under who were referred to clinics after eating products tainted with melamine. The children ate the foods every day for at least one month.

The study is one of the first to look at exposure to low doses of melamine, which was added to infant formula and other foods in China. Melamine is used to make plastics and fertilizers. It is high in nitrogen and when added to foods, it can mask low nutrient levels in standard tests.

"No severe adverse renal outcomes, such as acute renal failure or urinary tract obstruction, were detected in children after exposure to low dose melamine," Hugh Lam of the pediatrics department at the Chinese University of Hong Kong and his colleagues reported.

Two weeks ago, China's Health Ministry said six babies might have died after consuming tainted milk powder, and the number of infants sickened in the scandal was increased to nearly 300,000 since September, up from the previous total of 50,000.

Also two weeks ago, toxicology experts with the World Health Organization set a tolerable daily intake of melamine contamination in food at 0.2 milligrams of melamine per kilogram body weight each day, a standard Health Canada has adopted.

No melamine-related illnesses have been reported in Canada, Health Canada said. Melamine has been found in dairy products sold in Asia and to a lesser extent in Europe and North America.

In the Hong Kong study, the children were given urine tests, and ultrasound was used to examine their kidneys.

One child had a kidney stone, and seven had possible melamine-related deposits in their kidneys, the researchers said. None required treatment.

The prevalence of suspected melamine-related problems from ultrasounds tests was 0.2 per cent, the researchers concluded.

"These data suggest that large-scale and urgent screening programmes may not be informative or cost-effective for populations who have been exposed to low dose melamine," they wrote.