To provide care to people with autism spectrum disorder (ASD), it is imperative to screen for this disorder and to adequately diagnose it. Early evaluation can be useful. Diagnosis is best accomplished with standardized tests, developmental history and a clinical interview. The prevalence of ASD is 110 per 10.000.

Early intensive treatments appear to have the best outcomes. This emphasizes the need for early screening and diagnosis. Early diagnosis is affected by reluctance to express concern by parents (1), failure to be provided prompt assessment and diagnosis (2) and a failure of parents or professionals to detect signs of ASD (3). While ASD is believed to exist at birth, there are no biological markers and assessment and diagnosis thus relies on standardized tests and behavioural observation.

Parent observations are useful for early detection, especially speech regression (1), loss of motor skills (2), poor visual tracking (3) and a lack of joint attention (4). Factors that helped differentiate children with ASD from children with no or another developmental disorder were less looking at others (1), failure to respond to their name (2), less eye contact (3) and fewer positive facial expressions (4).

People with ASD are so heterogeneous that it is unlikely that there will be one gold standard for a test. To assess ASD, three things need to be taken into account.

• Early life scales (i.e. children from 1 to 3 years old).
• Progress across the lifespan on the core symptoms (i.e. communication; social skills; rituals; stereotypes).
• High-rate co-occurring problems (e.g. challenging behaviours; psychopathology).

It is essential to have a structured observation and attempts to elicit core symptoms. Historical data on developmental milestones, socialization and communication also need to be collected. Parents may over or underreport symptoms, as reflected by the lack of correlation between the clinician and the parent reports. In this case, another caregiver may need to be used (e.g. grandparents).

Early diagnosis increases parental stress and this could negatively impact the child with respect to behaviour problems and treatment outcomes. Using the DSM-5 criteria for ASD lead to a decrease in the prevalence. The DSM-5 may have higher specificity compared to the DSM-4 but a lower sensitivity. This means that mainly females will be missed according to the new criteria.

ASD is characterized by deficits in social skills (1), verbal and non-verbal communication problems (2) and repetitive behaviours or interests (3). Social skills deficits involve problems understanding and responding to social information. This includes problems with social imitation (1), joint attention (2), orienting to social stimuli (3), face perception (4), emotional perception and expression (5) and symbolic play (6). Communication deficits are characterized by delayed and problematic language development. This includes echolalia (1), abnormal prosody (2) and pronoun reversal (3). Repetitive behaviours or interests refer to invariant motor movements and insistence on routines and circumscribed interests. It includes stereotyped movements (1), toe walking (2),, finger flapping (3) and whirling (5). For the interests, it includes memorization of facts about a specific topic of interests.

When determining which instrument to use, validity and reliability need to be taken into account. It is also important to consider the feasibility of the test (e.g. time and effort to administer the test). Assessment must fit the individual’s age (1), goals (2), cognitive abilities (3) and developmental level of the areas being assessed (4).

It is useful to screen and assess at-risk populations for ASD (e.g. family members of children with ASD). Interviews are useful during the assessment period, especially with those who spend the most time with the child.

During observation, the child should have opportunities to play alone as well as interact with others. All three core features need to be assessed. Observational instruments refer to tools that can guide the clinician in what to look for or try to elicit during an observation to determine whether the core features are present and where and when this occurs.

Rating scales can be very efficient. It allows to gathering of more information about a child in a short time. These measures can be completed by the caregiver and only take a few minutes.

The DSM-5 uses one disorder for autism and does not use Asperger’s syndrome anymore. However, it may still be useful to screen for Asperger’s syndrome. Moreover, it remains important to assess symptoms of ASD in people diagnosed with Asperger’s syndrome. It may be useful to give people with ASD an intelligence test as ASD is comorbid with ID. It is also useful to measure adaptive behaviour.

The purpose of an initial ASD evaluation is to determine the presence and severity of an ASD and possible comorbid disorders (1), inform future intervention and treatment planning (2) and provide a baseline to evaluate treatment efficacy (3). This requires a diagnostic interview (1), rating scales (2), informal interviews (3) and observations in both the clinic and school setting (4). Interviews are conducted first to gain developmental and medical history and determine the existence of a clinically significant disorder. Next, the rating scales are administered to determine the amount, type and severity of symptoms. A complete evaluation includes an assessment of adaptive behaviour (1), communication and language (2), cognitive and academic assessment (3), developmental history (4) and a medical screening to discern comorbid or contributing factors (5).

Discrepancy between observers may be due to the different settings. This thus provides valuable information. ASD diagnoses at age three are generally stable. Milder ASD symptom presentation (i.e. PDD-NOS; Asperger syndrome) may be more difficult to identify in young children. Rule Out diagnoses refers to an approach in which the child has access to services (e.g. early intervention) but an incorrect diagnosis is avoided as it may be re-evaluated in an appropriate amount of time. This may be useful when there are low levels of ASD symptoms.

ASD symptomatology can be heterogeneous for children of the same age. Common symptoms associated with ASD have some overlap with other developmental disabilities. To assess whether symptoms represent ASD or another developmental disability, the clinician should assess for discrepancies between the individual’s overall developmental level and social communication skills. A significant discrepancy is more resembling of ASD.

There are also overlapping symptoms between ASD and specific language impairment. People with ASD are more likely to exhibit pragmatic language impairment. Language loss and broad regression is more typical of ASD than of SLI. However, both groups do show attention impairments, though the nature of these impairments may differ. For ASD, there may be deficits in executive functioning and deficits in auditory sustained attention and auditory selective attention as well as executive functioning for SLI.

Social abilities may be used to differentiate ASD from other developmental disabilities. Social attention behaviours (e.g. social orienting; joint attention) can be used to discriminate children with ASD from those with other disorders (e.g. other developmental disorders). The indicators include orienting eye gaze toward objects rather than people (1), ewer attempts to initiate or respond to bid of joint attention with primary caregivers (2) and displays of positive affect to non-social stimuli with neutral response to social stimuli (3).

People with ID and ASD often have similar symptoms (e.g. self-injurious behaviours; stereotypes). There is no single IQ profile that is indicative of ASD compared to another developmental disorder. Individuals with ASD often exhibit the ability to sustain attention for preferred activities but diminished ability to selectively attend to non-preferred stimuli. They may also have difficulty shifting attention. ID is the most prevalent co-occurring disorder with ASD (i.e. 40% - 71%). This is lower for people with PDD-NOS or Asperger (i.e. 6% - 49%).

Seizure disorders occur in 11% to 39% of the people with ASD. Over 70% of children with ASD meet the diagnostic criteria for a comorbid emotional or behavioural disorder. Bipolar disorder tends to rarely occur in children with ASD. The best way to identify comorbid mood disorders it to compare it to baseline behaviour. Children with ASD are also more likely to be diagnosed with a tic disorder. However, stereotypies (e.g. tapping) are not necessarily tics and are more likely to be rhymical rather than spasmodic.

Tests of intelligence with children with ASD may need to be modified (e.g. clearer structure; fewer verbal instructions; fewer changes from pattern). Children with ASD often display wide variations in cognitive abilities.