There is currently no specific test designed to diagnose autism. Instead, a diagnosis is made after the healthcare provider evaluates the patient's signs and symptoms. The healthcare provider will also talk with family members about their observations and interactions with the child. It may be helpful for the patient's family members to record observations of behaviour that seems abnormal.
If a healthcare provider cannot make a clear diagnosis, he/she may recommend other professionals that specialise in developmental disorders. Specialists, such as developmental paediatricians, psychiatrists, psychologists, and/or neurologists, may be recommended. In addition, other specialists, such as experts that test hearing (audiologists), speech and language pathologists, occupational therapists, social workers, and physical therapists, may also help diagnose the patient.
Although most signs of autism begin to develop when the child is 12-18 months old, most diagnoses are made when the child is two to three years old.
During a physical examination, the healthcare provider will observe specific behaviours. The healthcare provider typically looks to see how the child responds to commands or questions.
Some healthcare providers use screening tests, including the checklist for autism in toddlers (CHAT) or the autism screening questionnaire to determine whether or not a patient has autism. CHAT is a 16-question survey, in which parents or caregivers respond "yes" or "no" to questions about their children's behavior. This test helps healthcare providers diagnose autism in patients who are 18 months old or younger. The autism screening questionnaire, also called the pervasive development disorder (PDD) assessment scale, is a brief survey, in which parents or caregivers rate the patient's developmental difficulties as nonexistent, resolved, mild, moderate, or severe. This test helps healthcare providers diagnose autism in patients who are four years old or older.