Testing for Autism Spectrum Disorder in Adults
Adults suspected of having ASD require a comprehensive multidisciplinary evaluation by trained professionals using standardized diagnostic measures, specifically the Autism Diagnostic Observation Schedule (ADOS) and Autism Diagnostic Interview-Revised (ADI-R), as self-report screening questionnaires like the AQ have poor diagnostic accuracy and should not be used to triage referrals. 1, 2
Diagnostic Process
Initial Clinical Assessment
The diagnostic evaluation must be performed by clinicians trained in autism assessment using objective, standardized criteria. 3, 4 The assessment should include:
- Direct behavioral observation using the ADOS, which has a sensitivity of 91% and specificity of 76% in adults 5
- Structured developmental history interview using the ADI-R, which has sensitivity of 80% and specificity of 72% 5
- Comprehensive psychiatric evaluation to identify co-occurring conditions, as adults with ASD have significantly higher rates of depression (20% vs 7%), anxiety (11% vs 5%), and sleep difficulties (13% vs 5%) compared to the general population 5
Critical Limitations of Self-Report Screening Tools
Do not rely on self-report questionnaires like the Autism-Spectrum Quotient (AQ) or Ritvo Autism Asperger's Diagnostic Scale-Revised (RAADS-R) for diagnostic decision-making, as these tools have poor diagnostic validity in adults. 1, 2
Key evidence demonstrates:
- The AQ has extremely poor specificity of only 0.29 and produces 64% false negatives—meaning nearly two-thirds of adults who score below the cutoff actually have ASD 2
- In a specialty clinic sample, the RAADS-R had sensitivity of only 0.52 and specificity of 0.73, while the AQ had sensitivity of 0.45 and specificity of 0.52 1
- Generalized anxiety disorder can "mimic" ASD and inflate AQ scores, leading to false positives 2
- Adults diagnosed with ASD did not score significantly higher on self-report measures compared to those without ASD 1
Recommended Diagnostic Measures
Use the ADOS as the primary observational tool, as it demonstrates the highest sensitivity (0.94) among available measures for adults. 1 However, recognize that:
- The ADOS alone has moderate diagnostic accuracy (AUC = 0.69) and should not be the sole basis for diagnosis 1
- Multiple assessment methods must be combined, including structured interviews, direct observation, collateral information from family members when possible, and comprehensive psychiatric evaluation 1, 6
The newly developed Autism Clinical Interview for Adults (ACIA) shows promise as an adult-specific diagnostic interview, taking 60-90 minutes and accurately identifying core autism characteristics and co-occurring conditions 6
Essential Medical Workup
Mandatory Assessments
Every adult being evaluated for ASD must have a formal audiogram to rule out hearing loss that could mimic ASD symptoms. 7, 3, 4 This is a critical step before proceeding with further evaluation.
Genetic Evaluation
Offer genetic consultation to all adults with confirmed ASD, as a thorough clinical genetics evaluation identifies an underlying etiology in 30-40% of individuals. 7, 3
The tiered genetic testing approach includes:
First-tier testing:
- Chromosomal microarray (CMA): 10% diagnostic yield 3
- Fragile X DNA testing: 1-5% yield (males routinely; females if clinical indicators present) 7, 3
- High-resolution karyotype: 3% yield 3
Second-tier testing (based on clinical features):
- MECP2 gene testing in females: 4% yield 7, 3
- PTEN gene testing if head circumference >2.5 standard deviations above mean: 5% yield 7, 3
Evaluation by a clinical geneticist for dysmorphic features and family history analysis remains high-yield and cost-effective. 7, 3
Treatment Approach
Intensive behavioral interventions are first-line therapy, particularly focusing on improving language, play, and social communication skills, with small to medium effect sizes demonstrated. 3, 4, 5
Pharmacotherapy Indications
Medications are reserved for co-occurring psychiatric conditions and specific symptoms, not for core ASD features. 3, 4, 5
- For irritability and aggression: Risperidone or aripiprazole (standardized mean difference of 1.1, indicating large effect size), though these carry risks of appetite, weight, and sleep changes 5
- For co-occurring ADHD: Psychostimulants (standardized mean difference of 0.6, indicating moderate effect size) 5
- For anxiety and depression: Treat according to standard psychiatric guidelines, recognizing these conditions affect 11% and 20% of adults with ASD respectively 5
Genetic Counseling and Family Planning
Provide genetic counseling to all families regardless of whether a specific etiology is identified. 7, 3 For families without identified genetic cause, use empiric recurrence risk data:
- Full sibling recurrence risk: 3-10% 3
- Modified by sex: 7% if affected individual is female, 4% if male 3
- With two or more affected individuals: at least 30% recurrence risk 3
Critical Pitfalls to Avoid
Do not use the AQ or similar self-report questionnaires to screen or triage referrals to diagnostic services, as this approach would miss the majority of adults with ASD. 2 The UK NICE guidelines' recommendations supporting the AQ's screening role may need reconsideration based on current evidence 2
Do not delay diagnosis due to atypical presentation or co-occurring psychiatric conditions. 3 Anxiety disorders in particular can complicate the diagnostic picture and should be systematically assessed 8, 2
Do not order extensive genetic testing without clinical geneticist evaluation first, as the stepwise approach with higher-tier tests is more cost-effective 7, 3
Schedule periodic reevaluations for adults without a definitive etiology, as diagnostic technology and understanding continue to evolve 7, 3