Best Screening Tool for Suspected Autism in Adults
The Autism-Spectrum Quotient (AQ) is the most widely studied and accessible screening tool for adults with suspected ASD, but it has significant limitations in clinical diagnostic settings and should not be used alone to triage referrals for specialist assessment.
Primary Screening Tool: The Autism-Spectrum Quotient (AQ)
The AQ is a 50-item self-report questionnaire that measures autistic traits in adults with normal intelligence, with scores ranging from 0-50 1. A threshold score of ≥26 demonstrates good discriminative validity and screening properties in clinical practice 2. Adults with confirmed AS/HFA score significantly higher (mean 35.8) compared to controls (mean 16.4), with 80% of adults with AS/HFA scoring ≥32 1.
Critical Limitations of the AQ in Clinical Settings
Despite its widespread use, the AQ has poor specificity (0.29) and negative predictive value (0.36) in actual diagnostic clinic populations 3. In a study of 476 consecutive adult referrals to a specialist ASD diagnostic service:
- 64% of those scoring below the AQ cut-off were false negatives who actually had ASD 3
- While sensitivity was acceptable at 0.77, the high false-negative rate means many adults with genuine ASD would be incorrectly screened out 3
- Generalized anxiety disorder can "mimic" ASD and inflate AQ scores, leading to false positives 3
Recommended Clinical Approach for Adult ASD Screening
Do not use the AQ as a gatekeeping tool to deny specialist referrals. Instead, use the following algorithm:
Step 1: Initial Screening with AQ
- Administer the AQ as a preliminary measure (score ≥26 suggests possible ASD) 2
- Recognize that a score below threshold does NOT rule out ASD 3
Step 2: Comprehensive Clinical Assessment
All adults with suspected ASD require direct clinical evaluation regardless of AQ score, including:
- Structured diagnostic interviews using the Autism Diagnostic Interview-Revised (ADI-R) 3
- Direct behavioral observation using the Autism Diagnostic Observation Schedule-Generic (ADOS-G) 3
- Clinical diagnosis according to ICD-10 or DSM criteria by expert clinicians 3
Step 3: Screen for Psychiatric Comorbidities
- Systematically assess for anxiety disorders (particularly generalized anxiety disorder), mood disorders, OCD, and other psychiatric conditions that may confound the clinical picture 3
- Differentiate anxiety-driven behaviors from core ASD features 3
Important Clinical Pitfalls to Avoid
Do not rely solely on self-report screening tools for diagnostic decision-making. The AQ was designed to measure autistic traits dimensionally in the general population, not as a definitive diagnostic instrument 1, 4.
Do not use the AQ to prioritize or triage referrals to specialist services, as this will result in missing a substantial proportion (64%) of adults who genuinely have ASD 3. Current recommendations supporting the AQ's role in screening referrals (including UK NICE guidelines) may need reconsideration based on this evidence 3.
Do not assume that high-functioning adults were screened in childhood. Many intellectually capable adults with ASD were missed by childhood screening, as social disability in higher-functioning individuals is often detected later 5.
Convergent Validity Considerations
The AQ shows convergent validity with other established measures like the Social Responsiveness Scale (SRS) in high-functioning samples 6. However, this convergent validity does not overcome its poor specificity in clinical diagnostic settings 3.
Sex Differences in Screening
Men score slightly but significantly higher than women in the general population, with 4% of men scoring ≥34 compared to 0% of women 1. However, among those with confirmed AS/HFA, male and female scores do not differ significantly 1. This suggests potential under-detection of ASD in women using standard cut-offs.