Researchers have discovered that about one third of children who returned a positive result in a skin-prick test were actually able to eat peanuts safely.

Sydney Children's Hospital immunologist and University of New South Wales researcher Brynn Wainstein said the results show parents should not automatically accept a nut allergy diagnosis.

"Because peanut allergies are potentially serious, requiring all sorts of restrictions, families can become very anxious when, in fact, some of these families may be worrying unnecessarily," Dr Wainstein said.

The study involved 84 children who had been diagnosed with a peanut allergy without ever having eaten the nuts.

The children were thought to suffer an allergy because after having traces of peanut introduced into a small scratch made on their skin with a needle, they developed a hive larger than 8mm, which is the commonly accepted cut off size.

But the researchers found that about one third of children who then took a "peanut challenge", in which they ate peanuts while under observation in hospital, had no reaction.

After reviewing the results, the researchers found those children who were not allergic had all developed hives smaller than 13mm.

The result indicated the actual cut off level, when the test was performed in their clinic - and likely many other Australian clinics - was higher than the accepted standard.

The researchers concluded that the test was "very subjective", and may be affected by variables such as the equipment used and the pressure the doctor places on the skin.

"Essentially, the take home message was that if you don't know your child has a peanut allergy ... and the doctor says your child is allergic to peanut, you need to say: 'Are you sure?'," Dr Wainstein said.

He said for many parents it may be worth putting their children through the peanut challenge, which was the "gold standard" of testing.

"The only way to know, in some cases, whether the test means you're allergic is to do a food challenge," he said.

About one in 200 children will have an allergic reaction to peanuts by the age of five, in which their blood pressure drops and their tongue and throat swell, blocking the airway.

The reaction is potentially fatal, but can be counteracted if the child is quickly given an adrenaline injection.

Dr Wainstein said the researchers were further studying skin tests in an attempt to see if the size of the hive could predict children who would have severe a allergic reaction.

Source: AAP, News.com.