THOUSANDS of children diagnosed with autism could lose access to thousands of dollars in federal support and other subsidies under changes planned for the manual of medical disorders used to guide psychiatrists worldwide.
Autism patient advocates say the first Australian research on the likely impact of the changes suggests 23 per cent of those who qualify as having a form of autism would no longer do so.
Many of those who fail the new test would be classified under a new diagnostic category, called "Social Communication Disorder" which, under current arrangements, would not qualify children for support under a federal government package introduced in 2008.
Several independent studies conducted in the US have found fewer children would qualify for an autism diagnosis under the new criteria, in contrast to field work done by the American Psychiatric Association which has predicted no such outcome.
The country's largest not-for-profit, autism-specific service provider, Autism Spectrum Australia (Aspect), which conducted the research, says the findings could hold dire implications for many families who, since 2008, have been able to access up to $12,000 in funds over at least two years to help provide speech therapy and other treatments for children who are diagnosed before the age of six.
Other elements of the scheme allow autistic children to receive Medicare-funded treatment from audiologists, occupational therapists, psychologists, speech pathologists and others, provided a treatment plan has been drawn up by the time the child is 13.
Clinical psychologist Vicki Gibbs, manager of Aspect's diagnostic assessment service, said the new definitions, contained in the fifth edition of the American Psychiatric Association's Diagnostic and Statistical Manual of Mental Disorders, were likely to come into effect shortly after the DSM-5 was published in May.
Aspect's study, the first of its kind to be done in Australia, compared how 132 Australian children diagnosed with autism would have fared had they been assessed under the DSM-5.
The results showed 23.5 per cent failed to meet the new criteria, which will require children exhibit at least five out of a possible seven symptoms, instead of three as at present.
"I think it's unlikely (changes) would be applied to people with an existing diagnosis, until they are going into a situation where they are asked for an updated diagnostic statement," Ms Gibbs told The Australian. "There could be some issue then."
Sydney mother Rachel Laidlaw has three children, all affected by an autism spectrum condition: 10-year-old Oscar, who was diagnosed in 2010 aged eight, and nine-year-old identical twins Max and Hugo.
Hugo was diagnosed last year with an autism-spectrum condition called Pervasive Development Disorder Not Otherwise Specified.
Max was the only one of the three to qualify for the federal assistance program, as he was diagnosed when he was nearly four.
As a result of the diagnosis, he received weekly speech therapy sessions that taught him, for the first time, the skills that enabled him to hold a conversation.
"If families stop getting the support they need, that's going to make a huge difference -- and it will make a huge difference at school, because teachers need to know what the issues are so they can teach them," Ms Laidlaw said.
A spokeswoman for Families and Community Services Minister Jenny Macklin said it was up to health professionals to decide what tools and criteria to use in diagnosing autism in Australia, and support for children with autism was "based on the best advice from Australian health experts".