The relationship between carers' report of autistic traits and clinical diagnoses of autism spectrum disorders in adults with intellectual disability.

It is often difficult to determine the triad of impairments and whether autistic features are the consequence of intellectual impairment or autism spectrum disorders in people with intellectual disability (ID). The aim of the current study was to investigate the relationship between carer-reported autistic traits and independent diagnoses of autism spectrum disorders (ASD). Data were collected on carers' subjective report of autistic traits and clinical diagnoses of ASD. Of 1145 adults with ID identified, 220 (19%) individuals had a diagnosis of ASD, and 778 (68%) individuals had at least one autistic trait. Optimal sensitivity and specificity were achieved with two or more autistic traits (sensitivity 63%; specificity 79%) and the positive predictive value increased substantially as the number of autistic traits increased. However, a significant proportion of individuals with ID who did not have a diagnosis of ASD also displayed autistic traits. Our findings suggest that in the absence of other measures, the presence of autistic traits can serve as a useful proxy measure for ASD in research (and/or clinical settings). However, although information on autistic traits may help healthcare practitioners to identify people with possible ASD, it cannot be used alone to make a formal diagnosis.