Making a diagnosis

There's no autism blood test. It's diagnosed by observing behavior and some experts say gender-based differences highlight a need to develop different ways to evaluate boys and girls.

Autism screening is recommended for all kids at age 18 months and 2 years. But screening tools typically are based on research in autistic boys, says Rachel Loftin, clinical director of an autism center at Rush University Medical Center in Chicago.

One widely used screening questionnaire for parents focuses on social deficits seen more often in autistic boys than affected girls. Questions include "Does your child play make-believe, make eye contact, seek praise, show interest in other children?" Girls with autism, especially mild cases, often don't show obvious problems in those categories－they're more likely than affected boys to play pretend with toys rather than lining them up by size or shape. Loftin says they're also more likely to show concern for another person's feelings.

Government data show that all forms of autism－mild to severe－are more common in boys and that the average age at diagnosis is 4 years in boys and girls. But Loftin says anecdotal evidence suggests a two-year lag time in diagnosis for girls, especially those with mild cases. And she suspects many cases are missed or misdiagnosed. That means a delay in early intensive behavior therapy that is the main treatment for autism.

Some girls manage to camouflage symptoms until school pressures to fit in become overwhelming, delaying diagnosis until around age 8 or 9, says Alycia Halladay, chief science officer at the Autism Science Foundation, a nonprofit educational and research-funding group.

Prominent autism advocate, professor and author Temple Grandin didn't fit that mold. She wasn't fully verbal until age 4. "It was obvious something was drastically wrong with me," Grandin says. With "1950s parenting" including intense encouragement to develop social skills and other talents, she says she learned to adapt.