Reasons Why High-Functioning Autism Can Evade Diagnosis

Autism is a complex neurodevelopmental disorder that affects millions of people worldwide. A 2023 report from the Centers for Disease Control and Prevention (CDC) says that one in 36 8-year-old children in 2020 had an autism spectrum disorder (ASD) diagnosis. This was a marked increase from one in 44 children in 2018. Even though children can be diagnosed with autism spectrum disorder as early as 12 months of age, many of them aren't diagnosed until they reach school age.

"High-functioning" autism isn't an official diagnosis, and given its imprecision, the term is not without controversy. That said, of the three levels of autism spectrum disorder, those who might be described as "high-functioning" are typically diagnosed with level 1 autism spectrum disorder. These people can live independently because their symptoms don't meaningfully impede their ability to work, succeed at school, or form interpersonal relationships, according to PsychCentral. People with level 1 autism might seem to be socially awkward, emotionally sensitive, or fixated on strict routines, but they can evade an autism diagnosis until as late as adulthood for various reasons.

According to Child Mind Institute, children with ASD are often first diagnosed with attention-deficit hyperactivity disorder (ADHD) or sensory processing disorders by ages 2 or 3. It's not that ADHD and ASD are mutually exclusive — in fact, they share many of the same symptoms, and they can co-occur. At least a third of children with ASD also have ADHD, and sensory processing is a symptom of ASD. Doctors are often reluctant to diagnose a child with ASD because they recognize that children develop at different paces. This "wait and see" attitude can lead to a later diagnosis of ASD.

Additionally, many people who don't receive an early diagnosis of autism may go on to be misdiagnosed with psychological conditions. A 2014 study in Autism-Open Access investigated late-in-life autism diagnoses in people ranging from age 17 to age 50. Each of the case studies was of a person who sought help from mental health services for interpersonal relationship issues and problems in social situations. These case subjects were typically grammatically fluent and had good verbal communication skills — and the researchers note that their intellectual abilities may have prevented a childhood autism diagnosis. All had received some kind of psychiatric diagnosis, such as anxiety, depression, obsessive-compulsive disorder, among others — and it wasn't until they sought care from centers dedicated to ASD that they were eventually diagnosed with autism. 

A 2015 article in Molecular Autism found that boys are diagnosed with autism two or three times more often than girls. As the article points out, girls with ASD tend to show better social functioning than males, and they may display fewer repetitious behaviors — or those behaviors might manifest in less obvious ways. For instance, a preoccupation with dolls or reading books might not be seen as abnormal by parents and teachers. And, too, if a girl has a high IQ, she might have better language skills, memory, and cognitive flexibility than her male peers. This could cause ASD to be overlooked as a possible diagnosis.

This missed diagnosis doesn't make the life of a girl with ASD any easier. For instance, as shown in a 2021 case series published in Cureus, a girl with high-functioning ASD might struggle with her quality of life, underperform at work, or be socially excluded. Oftentimes, people with ASD are diagnosed with bipolar depression and look to those treatments for relief. A girl might be diagnosed with other issues, but the interventions won't be effective if they don't target autism.

High-functioning children with autism don't have as much trouble with language, which is usually one of the first symptoms of autism picked up at an early age, according to PediaPlex. It's not until a child reaches school that parents or teachers might notice problems with social interactions. Autism in general may not be picked up until children are intellectually and socially challenged at school.

Children with high-functioning autism can also learn to camouflage their behaviors, according to the 2021 case series published in Cureus, which might cause them to evade diagnosis. They mimic other people's behaviors to adapt to social situations — this might include learning to look others in the eye, or using particular gestures or words. This masking can be cognitively exhausting over time, however. That's why they seek help later in life with stress, anxiety, and depression. Camouflaging is also seen more often in females than males, per the article.

According to NPR, Latino and African-American children who are autistic receive their diagnoses at an older average age than white children, and a variety of factors may come into play. Some families might be unable to pay for the healthcare that could help treat children who show symptoms of autism. Other families might not understand how valuable an early diagnosis and treatment can be to a child's later outcomes. Some parents might not be confident enough to press their physicians to investigate their children's symptoms further, and physicians may miss key symptoms or mistake symptoms of ASD for behavioral problems. Finally, many families face daunting barriers to access healthcare — for instance, language, transportation, and healthcare staffing shortages are common issues, via Wolters Kluwer.

However, a 2023 press release from the CDC said that ASD diagnoses jumped by 30% from 2018 to 2020 among Asian, Black, and Hispanic children, according to a CDC analysis. The analysis suggested that improved awareness, screening, and access to underserved populations account for this increase — but the release emphasized there is still work to be done to ensure all children with autism receive the screening and support they need.

Children are often screened for autism at 18 and 24 months so they can receive early interventions to help with their development, according to the American Academy of Pediatrics. The autism assessment can be quite cumbersome and time-consuming, according to the Child Mind Institute. It typically takes about 30 minutes for an initial assessment combined with an interview with parents that could take several hours. Even then, a doctor can't always observe what parents see at home or how a child behaves in social situations.

Although 85% of children diagnosed with ASD had symptoms before age 3, only 42% of them were diagnosed at that age. Some signs of autism aren't seen until well after the screenings, so a diagnosis is often missed, according to the Center for Advanced Pediatrics. However, if children are diagnosed with autism early, parents and their doctors can help the children learn developmental skills to better function in their lives. They can receive treatments such as psychotherapy, cognitive-behavioral therapy, medication, and assistance from teachers.