Predicting the diagnosis of autism in adults using the Autism-Spectrum Quotient (AQ) questionnaire

Abstract

Background: Many adults with autism spectrum disorder (ASD) remain undiagnosed. Specialist assessment clinics enable the detection of these cases, but such services are often overstretched. It has been proposed that unnecessary referrals to these services could be reduced by prioritizing individuals who score highly on the Autism-Spectrum Quotient (AQ), a self-report questionnaire measure of autistic traits. However, the ability of the AQ to predict who will go on to receive a diagnosis of ASD in adults is unclear.

Method: We studied 476 adults, seen consecutively at a national ASD diagnostic referral service for suspected ASD. We tested AQ scores as predictors of ASD diagnosis made by expert clinicians according to International Classification of Diseases (ICD)-10 criteria, informed by the Autism Diagnostic Observation Schedule-Generic (ADOS-G) and Autism Diagnostic Interview-Revised (ADI-R) assessments.

Results: Of the participants, 73% received a clinical diagnosis of ASD. Self-report AQ scores did not significantly predict receipt of a diagnosis. While AQ scores provided high sensitivity of 0.77 [95% confidence interval (CI) 0.72-0.82] and positive predictive value of 0.76 (95% CI 0.70-0.80), the specificity of 0.29 (95% CI 0.20-0.38) and negative predictive value of 0.36 (95% CI 0.22-0.40) were low. Thus, 64% of those who scored below the AQ cut-off were 'false negatives' who did in fact have ASD. Co-morbidity data revealed that generalized anxiety disorder may 'mimic' ASD and inflate AQ scores, leading to false positives.

Conclusions: The AQ's utility for screening referrals was limited in this sample. Recommendations supporting the AQ's role in the assessment of adult ASD, e.g. UK NICE guidelines, may need to be reconsidered.

Keywords: Autism; autism spectrum disorders; neurodevelopmental disorders; screening; self-report.

Fig. 1.

Distribution of 10-item Autism-Spectrum Quotient (AQ10) scores in patients according to whether they subsequently received a clinical diagnosis of autism spectrum disorder (ASD). (a) Histograms showing the proportion of patients who did not receive an ASD diagnosis (left) and of those who did receive a diagnosis (right) scoring at each level on the AQ10 (score out of 10). (b) Proportion of those scoring at each level of the AQ10 who received an ASD diagnosis. Values are means, with standard errors (s.e.m.) represented by horizontal bars. For a colour figure, see the online version.