Identification and Diagnosis of Autism Spectrum Disorders: An Update

Greg Pasco


Pediatr Health. 2010;4(1):107-114. 

In This Article

Diagnostic Instruments

The most widely used and best validated diagnostic assessment is the Autism Diagnostic Observation Schedule (ADOS),[16] a semi-structured interactive assessment administered by a trained examiner. There are four modules, with the appropriate module selected according to the age and expressive language level of the person being assessed: module 1 is designed for young nonverbal children and module 4 for use with verbally fluent adolescents and adults. The examiner interacts with the child or adult in a number of developmentally appropriate tasks and scores specific behaviors according to prescribed criteria. Scores of key items from communication and social interaction domains contribute to a diagnostic algorithm. Cut-off scores indicate whether outcomes meet criteria for autism or autism spectrum (broadly mapping onto DSM and ICD definitions of core autism and PDD-NOS respectively). Currently, the diagnostic algorithm does not include scores of items relating to restricted, repetitive and stereotyped behaviors; therefore, a full clinical diagnosis must be supplemented by information from other sources.

The Autism Diagnostic Interview – Revised (ADI-R)[17] is the most established autism-specific diagnostic interview and consists of 93 questions relating to current skills and behaviors, as well as in relation to how these behaviors were manifest at 4–5 years of age (or 'ever' in some cases). Scores from items in domains relating to communication, social interaction, repetitive and stereotyped behaviors and the age of onset contribute to an overall diagnostic algorithm total, yielding outcomes relating to DSM and ICD definitions of core autism only. The combined use of the ADOS and the ADI-R improve the accuracy and reliability of ASD diagnosis,[18,19] although, as it can take between 2 and 3 h to administer the ADI-R, this may be too time-consuming for many clinicians. Alternative diagnostic interviews include the Diagnostic Interview for Social and Communication Disorders (DISCO)[20] and the Developmental, Dimensional and Diagnostic Interview (3di),[21] both of which offer a broader range of diagnostic outcomes, although they are generally not any quicker to administer than the ADI-R. There is little evidence to distinguish between the various diagnostic interviews, but it is recommended that training in at least one of these methods combined with an understanding of ASD will lead to greater confidence in a diagnosis even if these instruments are not used every time.[22]

Mazefsky and Oswald compared the diagnostic outcomes from the ADOS and the ADI-R with the consensus clinical diagnosis of a specialist clinic team, based on DSM-IV criteria.[23] Diagnostic agreement with the team diagnosis was 77% with false-positives of 16% for both instruments, indicating a slight tendency to 'overdiagnose'. In clinical settings this over-identification is unproblematic, as expert judgment will moderate this and cases are less likely to be missed. In addition to assessments used for diagnosis, several assessments have been demonstrated to be useful for assessing cognitive and language abilities in children with, or suspected of having, an ASD.[24]


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