Researchers have provided an update on the best known ways to tell if a child has autism.

Autism is traditionally diagnosed with behavioural tests to assess kids against developmental milestones such as talking, interacting with their families, and learning the nuances of social situations.

But researchers are still working on other ways, identifying more than 100 genes with a link to higher risk of developing autism.

Stephen Scherer, director of the centre for applied genomics at the Hospital for Sick Children in Toronto, has led a team in a comparison test to rate how the genetic tests match up against each other and against behavioural evaluations.

The study involved 258 children with autism spectrum disorder (ASD).

They had all had genetic testing to look at abnormalities in the chromosome, while some had more extensive whole-exome sequence genetic tests done too.

The researchers found that the two genetic tests were almost equally capable of detecting autism, with a success rate of 8 to 9 per cent.

But regardless of similarity, labs and clinicians are beginning to favour whole-exome sequencing.

Scherer says it is concerning because the two genetic tests are capable of spotting different markers for different kinds of autism.

When used together, the tests were found to diagnose ASD in nearly 16 per cent of cases.

“We need to use both technologies now,” he said in a recent interview for TIME magazine.

“If we only used one, we would miss some important information.”

It does not come cheap - chromosome-based tests costing close to $1,000, and exome sequencing slightly more.

Ideally, the research suggests, if a child is referred to a developmental paediatricians who suspect autism both tests should be done.

The research group also looked at how non-genetic evaluations could boost the results of genetic testing.

They divided the children into three groups based on whether brain scans showed they has physical differences that might indicate autism.

For children with evidence of physical abnormalities, the addition of the two types of genetic testing was able to diagnose autism in 37.5% of cases.

The findings suggest that the most accurate diagnosis of autism comes when all three types of tests are combined.

In fact, coming at the problem from various directions could actually help categorise the type of autism that a child may have.

“We need to start looking at each autism case individually, and come up with the best recommendations,” Scherer said.

If a parent suspects their child may inhabit some part of the autism spectrum, the researchers say their results point to behavioural testing as the first step.

This should be followed by chromosomal testing, and if that is negative, Scherer argues that whole exome sequencing might be useful in many cases.

“The message is that we need to use all technologies to get as much detailed information as we can to marry them all together,” he said.