How is Autism Spectrum Disorder (ASD) diagnosed and who should make the diagnosis?

Autism Spectrum Disorder Diagnosis

The diagnosis of ASD must be made by a professional specifically trained in diagnosing autism using objective criteria and standardized diagnostic tools—this should not be attempted by clinicians without this specialized training. 1, 2

Who Should Make the Diagnosis

Trained professionals with expertise in ASD diagnosis should confirm the diagnosis, which may include:

• Developmental-behavioral pediatricians 2, 3
• Child psychiatrists or psychologists with ASD training 4, 3
• Neurologists with developmental expertise 2
• Clinical geneticists (particularly when syndromic features are present) 1, 2

The primary care physician may raise the initial concern and perform screening, but depending on their training and comfort level, should typically refer for diagnostic confirmation rather than making the diagnosis themselves. 1

Diagnostic Process

Pre-Diagnostic Requirements

Before proceeding with ASD evaluation, every patient must have a formal audiogram to rule out hearing loss that could mimic ASD symptoms—this is non-negotiable. 1, 2, 3

Standardized Diagnostic Measures Required

The diagnosis cannot rely on clinical impression alone. Use these validated tools:

• Autism Diagnostic Observation Schedule-Second Edition (ADOS-2): sensitivity 91%, specificity 76% 2, 5
• Autism Diagnostic Interview (ADI): sensitivity 80%, specificity 72% 2, 5

The evaluation must include semistructured direct observation of behavior and semistructured caregiver interview using these standardized measures. 5

Core Diagnostic Criteria

DSM-5-TR requires deficits in all three areas of social communication/interaction across multiple settings, plus at least two restricted/repetitive behaviors, not explained by another condition and causing functional impairment. 6

Specific behavioral markers to assess include:

• Social attention deficits: reduced eye contact, limited social smiling, fewer nonverbal behaviors to initiate shared experiences 2, 3
• Communication impairments: no response to name, limited use of gestures, lack of imaginative play 3, 5
• Repetitive behaviors: atypical object use, rigid patterns of behavior 2, 3

Additional Assessments

• Cognitive testing 1
• Review of developmental history and past records 1, 4
• Family interviews when possible 4, 3
• EEG only if clinical suspicion of seizures 1

Role of Primary Care

Every individual with ASD should have a designated primary care medical home to coordinate care. 1, 2, 3

The primary care physician should:

• Screen all children at 18 and 24 months using validated tools like M-CHAT during routine well-child visits 2, 3, 6, 7
• Perform routine developmental surveillance at all visits 6, 7
• Refer promptly when concerns arise—diagnostic assessment should start within three months of referral 8
• Partner with specialists in ordering and coordinating diagnostic testing after genetics consultation 1

Genetic Evaluation

A genetic consultation should be offered to all persons and families with ASD, as this identifies an underlying etiology in 30-40% of individuals. 1, 2

First-Tier Genetic Testing

After ASD diagnosis is confirmed, order:

• Chromosomal microarray (CMA): 10% diagnostic yield 2, 3
• Fragile X DNA testing: 1-5% yield 1, 2, 3
• High-resolution karyotype: 3% yield (if not already performed) 1, 2

Second-Tier Testing (Clinically Indicated)

• MECP2 gene testing in females only: 4% yield 1, 2, 3
• PTEN gene testing if head circumference >2.5 SD above mean: 5% yield 1, 2, 3

Evaluation by a clinical geneticist for dysmorphic features remains high-yield and low-cost for distinguishing syndromic from isolated ASD. 2, 3

Critical Pitfalls to Avoid

• Do not delay diagnosis due to misconceptions about presentation, particularly in adults or atypical cases 4, 2, 3
• Do not rely on screening tools alone to rule out ASD—they identify increased risk but cannot exclude the diagnosis 8
• Do not order extensive genetic testing without clinical geneticist evaluation first—the stepwise approach is more cost-effective 2, 3
• Do not use any single autism-specific diagnostic tool alone to make the diagnosis 8
• Do not skip the audiogram—hearing loss must be ruled out first 1, 2, 3

Genetic Counseling

Provide genetic counseling to all families regardless of whether an etiology is identified. 1, 2, 3

For families without identified etiology, use these empiric recurrence risks:

• Full sibling recurrence: 3-10% (newer studies suggest potentially higher) 1, 2
• Modified by sex: 7% if affected child is female, 4% if affected child is male 1, 2
• With two or more affected children: at least 30% recurrence risk 1, 2

Follow-Up

Schedule periodic reevaluations for patients without definitive etiology, as diagnostic technology and phenotype understanding continue to evolve. 1, 2