Despite advances in autism diagnosis, one in four teens who are on the spectrum lack a formal diagnosis, researchers say.

In a study looking at health and educational records for 4,875 residents of four northern New Jersey counties who were age 16 in 2014, researchers found that about 1 in 55 satisfied the criteria for autism. However, about a quarter of them were undiagnosed.

Most of the teens without a diagnosis had a milder level of impairment, according to findings published recently in the Journal of Autism and Developmental Disorders.

Researchers warn that these individuals are losing out on support that could be beneficial.

“We think this is the largest ever study of ASD in this age group, and we hope it helps schools, health care providers and others with information that leads to better understanding and services,” said Walter Zahorodny, an associate professor at Rutgers New Jersey Medical School and the lead author of the study.

The data was collected as part of surveillance efforts through the Centers for Disease Control and Prevention’s Autism and Developmental Disabilities Monitoring Network, which routinely tracks prevalence in communities across the nation.

Consistent with previous studies, the data showed that those with autism were more likely to be male, white and from high-income families. In addition, the majority of teens with autism have one or more psychiatric conditions, most commonly attention deficient hyperactivity disorder.

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