What is the recommended approach for screening and diagnosing autism in adults, particularly those with a family history or symptoms of social anxiety and developmental delays?

Screening for Autism in Adults

Adults with suspected autism should undergo comprehensive diagnostic evaluation by clinicians trained in autism assessment using standardized tools (ADOS and ADI-R), not screening instruments, as validated screening tools for adults are limited and the diagnostic process differs fundamentally from pediatric screening. 1

Why Screening Differs in Adults vs. Children

The evidence base for autism screening focuses almost entirely on pediatric populations, with recommendations for screening at 18 and 24 months using tools like the M-CHAT-R/F. 2, 3 However, these pediatric screening approaches do not translate to adult populations where individuals present with different clinical contexts, compensatory strategies, and often seek evaluation after years of functional difficulties. 4, 5

Recommended Diagnostic Approach for Adults

Initial Clinical Assessment

Proceed directly to comprehensive diagnostic evaluation rather than screening when an adult presents with concerns about autism, particularly with family history, social anxiety, or developmental delays. 1 The evaluation must include:

• Formal audiogram to rule out hearing loss that could mimic ASD symptoms 1
• Comprehensive psychiatric evaluation to identify co-occurring conditions (depression occurs in 20% vs 7% in general population; anxiety in 11% vs 5%; sleep difficulties in 13% vs 5%) 1
• Structured diagnostic interviews using the Autism Diagnostic Interview-Revised (ADI-R) 1
• Direct behavioral observation using the Autism Diagnostic Observation Schedule (ADOS) 1, 6

Genetic Evaluation

Offer clinical genetics consultation to all adults with confirmed ASD, as this identifies an underlying etiology in 30-40% of cases. 1 The tiered approach includes:

First-tier testing:

• Chromosomal microarray (CMA) with 10% diagnostic yield 1
• Fragile X DNA testing with 1-5% diagnostic yield 1
• High-resolution karyotype with 3% diagnostic yield 1

Second-tier testing based on clinical features:

• MECP2 gene testing in females (4% diagnostic yield) 1
• PTEN gene testing if head circumference >2.5 SD above mean (5% diagnostic yield) 1

Available Adult Assessment Tools

Limitations of Current Instruments

No screening or diagnostic tool designed for children has satisfactory measurement properties when used in adults. 7 Among adult-specific instruments, only the Autism Spectrum Quotient (AQ-50, AQ-S) and Ritvo Autism Asperger Diagnostic Scale (RAADS-R, RAADS-14) show satisfactory or intermediate psychometric properties, but these have significant risks of bias and concerns about applicability. 7

The Autism Clinical Interview for Adults (ACIA) shows promise as a semistructured interview taking 60-90 minutes, covering autism traits and co-occurring conditions, though it requires further validation. 8

Critical Gaps in Adult Assessment

The lack of validated adult-specific diagnostic tools represents a major barrier to quality assessment. 4, 7 Current practice must rely on clinical expertise combined with available instruments, recognizing their limitations. 7

Special Considerations for Adults

High-Risk Populations

Adults with family history of autism warrant immediate comprehensive evaluation rather than screening, as full siblings have 3-10% recurrence risk (7% if affected sibling is female, 4% if male). 1 Social disability in intellectually able individuals is often detected later, as compensatory strategies may mask core features during childhood. 6

Post-Diagnostic Support

Adults experience strong emotions after diagnosis and require post-diagnostic support, yet services remain limited. 4, 5 The diagnostic process is often unclear and inconsistent across providers. 4, 5

Common Pitfalls to Avoid

• Do not use pediatric screening tools (M-CHAT, PEDS) in adults, as these were designed and validated only for children 18-30 months. 2, 3
• Do not delay comprehensive evaluation if autism is suspected; proceed directly to diagnostic assessment rather than attempting to screen first. 1
• Do not overlook co-occurring psychiatric conditions, which occur in approximately 75% of autistic adults and require separate treatment. 1, 3
• Do not rely solely on external observation; incorporate self-report measures capturing internal experiences not externally observable. 4
• Do not skip genetic evaluation and counseling, as this provides critical information for medical management, family planning, and empowerment. 2, 1

Treatment Implications

Intensive behavioral interventions remain first-line therapy for adults with ASD, focusing on language, play, and social communication skills. 1 Medications (risperidone, aripiprazole) serve only as adjunctive treatment for co-occurring psychiatric conditions and maladaptive behaviors, not for core ASD features. 1, 3