Diagnosis of autism is difficult since it is a complex disorder and no two individuals with the disorder have similar manifestations. There are no medical tests like a blood test that can help diagnose the disorder. In addition, autism may be manifested as a wide range of disorders and is thus termed Autism spectrum disorders (ASD).

Diagnosis is usually made by looking at the child’s behaviour and development. Most ASDs are detected in a toddler by the time the child is 18 months or younger.  By age 2, a diagnosis by an experienced professional can be made with relative accuracy. Final diagnosis however may be reached at a much later age.

Diagnosis involves two basic steps.

Developmental Screening

This is a short test to tell if the child is learning basic skills as appropriate for his or her age or if there are any delays. Parents are asked questions or are asked to talk or play with the child while being observed by the physician. This shows how the child learns, speaks, behaves, and moves while interacting with the primary caregiver or the parent. A delay in any of these areas could be a sign of a problem. 

Developmental screening is important for all children disabilities during regular well-child doctor visits. These are usually scheduled at 9 months, 18 months, 24 or 30 months and additional screening visits if the child is at a higher risk of developmental problems due to preterm birth, low birth weight or other reasons. Common reasons include a family history of mental retardation or autism, a sibling history of the same, another coexisting condition like Fragile X syndrome, Tuberous sclerosis, Down’s syndrome or Angelman’s syndrome.
 

All children need to be screened specifically for ASDs during regular well-child visits. These are scheduled at 18 months and then again at 24 months. Additional screening might be needed if a child is at high risk for ASDs. This includes children with someone in the family (e.g. parent or sibling) with ASDs and those with developmental problems due to preterm birth, low birth weight.

Screening tools are designed to help identify children who might have developmental delays. They cannot make a confirmatory diagnosis. These include Ages and Stages Questionnaires (ASQ), Communication and Symbolic Behavior Scales (CSBS), Parent's Evaluation of Development Status (PEDS), Modified Checklist for Autism in Toddlers (M-CHAT) and Screening Tool for Autism in Toddlers and Young Children (STAT) etc.

Comprehensive Diagnostic Evaluation

This is the second step in diagnosis of ASD. If the doctor detects problems on initial screening they may suggest a comprehensive diagnostic evaluation. This is a more thorough review that looks at the child’s behavior and development and interviews the parents. It may also include other tests like those for hearing and vision screening, genetic testing, neurological testing, and other medical testing.

This evaluation is performed by specialists including Developmental Pediatricians (specialists who work with child development and children with special needs), Child Neurologists (who specialize in brain, spine, and nerves and related disorders of children) and Child Psychologists or Psychiatrists (who specialize in pediatric psychiatry).

Algorithm for screening and evaluation of Autism spectrum disorders: