SAN FRANCISCO — An 18-month-old child who scored above the threshold for autism spectrum disorders on the Autism Diagnostic Observation Schedule was more than six times as likely to have a clinical diagnosis of autism spectrum disorder at the age of 3 years than one who scored lower, Dr. Lonnie Zwaigenbaum reported in a poster presentation at the annual meeting of the Pediatric Academic Societies.
Nevertheless, scores on the Autism Diagnostic Observation Schedule (ADOS) must be interpreted with caution in children who are 18 months old, wrote Dr. Zwaigenbaum of McMaster University, Hamilton, Ont., and his colleagues. ADOS scores should be interpreted in the context of an overall clinical assessment, because the test has a high sensitivity but a relatively low specificity, missing more than 50% of the children with diagnoses at 3 years.
The study involved 101 children who were at increased risk of autism by virtue of having an older sibling with autism. Also included in the trial were 42 control children with no increased risk of autism.
The children were assessed with ADOS and the MacArthur Communicative Development Inventory at the average age of 18 months, and they received a blinded diagnosis by an expert clinician at an average age of 39 months. This diagnosis was based on the clinician's best judgment following a comprehensive assessment that included the ADOS, the DSM-IV, and the Autism Diagnostic Interview-Revised.
The ADOS scoring algorithm includes one cutoff score for autism spectrum disorders (ASD) and a higher cutoff score for autism. Only one of the control children scored in the ASD range at 18 months, but that child was in the not ASD range at 24 months and did not have a diagnosis of ASD at 3 years. Using the autism cutoff, the 18-month assessment identified 9 of 20 children who ended up with a clinical diagnosis at 3 years (sensitivity of 45%) and 6 of 81 children who did not receive a diagnosis at age 3 (specificity of 93%). The meeting was sponsored by the American Pediatric Society, Society for Pediatric Research, Ambulatory Pediatric Association, and American Academy of Pediatrics.