Reasons Why High Functioning Autism Is Hard to Diagnose

High functioning autism (HFA), sometimes called mild autism or (until 2013) conflated with Asperger syndrome, is often diagnosed when individuals are teens or adults. But to qualify for an autism diagnosis, symptoms must be present from early childhood.

This means that the person being diagnosed as an adult has always had symptoms of autism, but somehow those symptoms flew under the radar for years. High functioning autism can be tough to diagnose in a very young child. Still, there are a number of answers that might help to answer that question.

Teenage girl talks to school counselor
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Masked Symptoms

Higher intelligence and language skills may have masked certain symptoms. The ability to do well in school, communicate effectively, and pass an IQ test with flying colors are all impressive—and may send parents and teachers down the wrong path when looking for reasons for a child's unusual issues or behavior.

Even general practice pediatricians can miss signs of autism when a child is able to communicate intelligently using spoken language.

In some cases, kids' strengths carry them through early elementary school with only minor issues, but become serious concerns when schoolwork becomes more abstract, demanding, and verbal—and when social interactions become more complex. 

Early Misdiagnoses

The individual may have received a number of other, related diagnoses while the underlying autism went undetected. Many people with autism also have diagnoses of attention-deficit hyperactivity disorder (ADHD), obsessive-compulsive disorder (OCD), social anxiety disorder (SAD), and other developmental or mental disorders.

A child with another diagnosis may not be properly evaluated for autism until later in childhood or even into adulthood.

According to research published in the journal Autism, 10.3% of adults with autism were incorrectly diagnosed with ADHD as children, while 12.1% of children initially diagnosed with ADHD were subsequently diagnosed with autism.


The individual may have been born before the diagnosis of Asperger syndrome or high functioning autism was included in the diagnostic literature. There were plenty of kids with symptoms consistent with HFA before 1994 when Asperger syndrome was added to the diagnostic manual along with other "milder" forms of autism. 

These individuals may or may not have received a diagnosis of something other than autism (autism would have been far too extreme a diagnosis for a high functioning individual)—and they may never have thought of seeking a new diagnosis as an adult.

Hidden Symptoms

The individual may have developed the means to hide, manage, or overcome their symptoms. People with high functioning autism are, by definition, of average or above-average intelligence.

If they are told often enough to make eye contact, stop rocking, flapping, or talking about the same things over and over again—they are often able to either hide, control, or actually overcome the need to present overt symptoms.

When that happens, the obvious external signs of autism are not present, making diagnosis very tricky indeed.

Female Sex

Some research suggests that women and girls are under-diagnosed with autism. While four times as many boys and men are diagnosed with autism than women and girls, the reasons are not clear. 

Are girls really less likely to be autistic? Or are their behaviors (apparent shyness, discomfort with public speaking, difficulties with motor coordination, confusion over social communication in situations such as team sports) considered "feminine" rather than problematic?

Or do girls with high-functioning autism actually behave differently from boys with autism, tending to be less aggressive, more imitative, and more likely to work hard to "fit in?" 

A 2015 study suggests that females are immune to some of the symptoms of autism (a condition referred to as the "female protective effect"). The theory suggests that symptoms of autism manifest differently in women and girls and that females tend to demonstrate better functional social behavior compared to males with autism.

While the reasons are not well understood, it seems clear that being a female on the spectrum may make you less likely to receive a diagnosis.

Income and Ethnicity

Individuals from poorer and/or minority backgrounds are under-diagnosed with autism. There seem to be two major reasons for this disparity.

The first and most obvious is that people with less money have less access to behavioral healthcare—and so are less likely to be able to access services, particularly for a child who is not obviously autistic. 

The second reason seems to relate to cultural differences: in some communities, the "oddnesses" associated with high functioning autism are not considered to be particularly problematic. And, of course, for recent immigrants, it's not surprising to hear that their child is not fitting in perfectly with American or "first-world" cultural norms.

Studies have long shown that poverty and racial inequality result in reduced access to healthcare and poorer quality of care. This translates to lower rates of autism diagnoses as well as poorer outcomes for autistic children who are diagnosed.

A Word From Verywell

It's important to remember that people who are diagnosed as adults may have had many challenges throughout their lives. In fact, many people diagnosed with autism as adults have struggled to find acceptance all their lives.

While a diagnosis doesn't necessarily change the course of autism, it can open the doors to understanding, therapies, and support that would not otherwise be available.

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