Agreement and Accuracy of ASD Diagnostic Instruments in a Sample of Adults with Average or Above-Average Intelligence

Background: The main tools currently used for the diagnosis of Autism Spectrum Disorders (ASD), the Autism Diagnostic Observation Schedule (ADOS) and the Autism Diagnostic Interview-Revised (ADI-R), have been tested in children samples in the vast majority of published literature. However, the number of diagnoses of ASD in adulthood is constantly increasing, often representing a challenge in clinical practice. To the best of our knowledge, very few studies have addressed the reliability of the diagnostic instruments in adult high-functioning individuals.

Objectives: The present study aims to evaluate the agreement among the DSM-5 criteria, the ADOS-2 and the ADI-R scores in a sample of adults with average or above-average intelligence. Additionally, sensitivity and specificity of the diagnostic instruments will be analyzed by means of ROC curves.

Methods: From June 2013, the Autism Lab of the University of Pavia recruited 84 patients meeting the following inclusion criteria: (1) age>18 years; (2) IQ>70; (3) good comprehension of written and spoken Italian. The ADOS-2 Module 4 was administered to all patients and the ADI-R was administered to their parents or caregivers, when available. A clinical diagnosis was performed by a senior psychiatrist according to DSM-5 criteria. Statistical analysis was conducted using SPSS 21.0.

Results: 67% of our sample met diagnostic criteria for ASD. The agreement between DSM-5 criteria and ADOS-2 scores was substantial (k=0.76). On the contrary, the ADI-R fairly agreed to DSM-5 criteria (k=0.36). The accuracy resulted to be good in ADOS-2 (AUC=0.87) and fair in ADI-R (AUC=0.75).

Conclusions: Our results confirm that ADOS-2 Module 4 is a reliable instrument for the diagnosis of ASD also in adult patients with average or above-average intelligence and good verbal fluency. On the contrary, the ADI-R appears less sensible and specific for ASD diagnosis in adults.