Medical professionals can' rely solely on their clinical judgment to detect autism risk, according to a recent study.

Researchers at Brigham Young University found that 10-20-minute observations, such as a pediatric exam, don't provide enough information about symptoms associated with autism. Within that short window, many children with autism display mostly typical behavior and may fail to receive a referral for further autism testing, even if a few autism symptoms are noticed.

"One of the biggest problems with early identification of autism is that many children aren't identified until they reach the school system," Terisa Gabrielsen, lead author of the study, said in a statement. "This means that they have missed out on some prime years for intervention that can change a child's outcome."

Last year the United States Centers for Disease Control and Prevention (CDC) released a report stating that 1 in 68 U.S. children has an autism spectrum disorder (ASD). That's a 30 percent increase from 1 in 88 from two years earlier. These increases mean an increased demand for autism referral decisions.

For the study, researchers looked at children 15-33 months old, with autism experts analyzing 10-minute videos of the children's behaviors during evaluation in a clinical setting.

They found that within the brief timeframe of 10 minutes, children with autism exhibited much more typical behavior than atypical behavior overall, making it easy for clinicians to miss detecting autism risk. In the study, even the experts who reviewed the videos missed referrals for 39 percent of the children with autism, based on the brief observation alone.

"It's often not the pediatrician's fault that referrals are missed," Gabrielsen said. "Even autism experts missed a high percentage of referrals within that short timeframe. Decisions for referral need to be based on more information, including autism screening and information from parents. We're hoping that this information can really empower parents to talk with pediatric care providers about their concerns."

The American Academy of Pediatrics recommends formal screening for autism at 18 and 24 months, but universal screening has not been fully adopted in pediatric primary care. The screening tools are also available for parents. These simple, standard tools for autism screening, such as the M-CHAT-R checklist and the CDC's Learn the Signs. Act Early campaign, are not perfect, but they are freely available, and can help parents learn what to look for as their child develops.

"Certainly, some young children with autism are clearly impaired and easy to recognize," said one of the other authors on the study Judith Miller. "However, this study looked at the entire range of children who present to the pediatrician's office, and we found that many children's impairments are not immediately obvious. For those children, formalized screening instruments and more time with a specialist may be critical."

The findings are detailed in the journal Pediatrics.