The study published in the Medical Journal of Australia on Monday found almost 3 per cent of the 256 most commonly-purchased manufactured food labelled "gluten-free" did not comply with the national standard.

The results were particularly concerning for coeliac patients whose health depended on a strict gluten-free diet, said lead researcher Dr Jason Tye-Din, head of coeliac research at the Walter and Eliza Hall Institute and gastroenterology consultant at the Royal Melbourne Hospital.

“It’s troubling to think that these foods could be hindering the careful efforts of patients trying their best to avoid gluten," Dr Tye-Din said.

"Patients who require a strict gluten-free diet for their treatment should be able to trust that food labelled as ‘gluten-free’ is what it says it is."

The researchers tested supermarket-bought noodles, muesli bars, chips, rice snacks and dry pasta that were promoted as "gluten-free".

Seven samples from six manufacturers contained gluten at levels of up to 49 parts per million (or 49 milligrams per kilogram), the researchers found.

“We found that 2.7 per cent of foods labelled ‘gluten-free’ were not compliant with the national standard of no detectable gluten," the report said.

"Two [products] contained gluten at levels exceeding the less strict Codex Alimentarius CODEX (Europe) and Food and Drug Administration (United States) thresholds for 'gluten-free' labelling.”

The report authors said the levels of gluten detected in the products were generally low.

However, one type of gluten-free pasta contained more than 3 milligrams of gluten in a standard single serve.

That level of gluten “could be harmful [for coeliacs], especially if consumed frequently”, the report said.

The researchers notified the manufacturers of products containing detectable gluten and urged them to conduct more frequent testing to improve detection.

“The findings indicate that gluten contamination does occur in packaged food available in Australia, and is generally not restricted to a single batch of food," Dr Tye-Din said.

“In addition, many of the items that failed the test were produced in dedicated gluten-free factories, so gluten contamination of externally sourced ingredients may be a factor and should be carefully examined," he said.

The study follows findings in May from the same group of researchers, whose survey of 128 Melbourne eateries found many foods promoted as "gluten-free" contained detectable gluten.

"Our findings indicate that inadvertent gluten ingestion is more likely when dining out than when consuming manufactured 'gluten-free foods'," the report said.

"Nevertheless, more frequent gluten testing, feasible for many companies, would reduce the risk for people with coeliac disease."