What is the process for diagnosing Autism Spectrum Disorder (ASD)?

Diagnosis of Autism Spectrum Disorder

Autism Spectrum Disorder is diagnosed through a structured process involving universal screening at 18 and 24 months, followed by comprehensive evaluation using standardized diagnostic tools (ADOS-2 and ADI-R) administered by trained professionals, with mandatory audiologic testing and genetic evaluation. 1

Initial Screening Process

• Screen all children at 18 and 24 months during routine well-child visits using the Modified Checklist for Autism in Toddlers (M-CHAT), even without specific parental concerns. 1

• Key early warning signs between 12-24 months include:

  • Reduced eye contact and social smiling 1
  • Limited nonverbal behaviors to initiate shared experiences 1
  • Atypical object use and repetitive behaviors 1
  • No response to name when called 2
  • Lack of imaginative or pretend play 2

Diagnostic Confirmation

The diagnosis must be confirmed by professionals trained in autism assessment using objective, standardized criteria. 3, 4

Required Diagnostic Tools

• Autism Diagnostic Observation Schedule-Second Edition (ADOS-2): sensitivity 91%, specificity 76% 1, 2
• Autism Diagnostic Interview-Revised (ADI-R): sensitivity 80%, specificity 72% 1, 2

Comprehensive Assessment Components

• Direct observation focusing on social interaction patterns and restricted/repetitive behaviors, modified based on developmental level 1

• Detailed developmental history including:

  • Timing of symptom onset 1
  • Any regression history 1
  • Response to previous interventions 1
  • Family psychiatric history 1

• Interviews with the individual and family members when possible, with review of past records 3

• Physical examination including Wood's lamp examination for tuberous sclerosis signs 1

• Cognitive testing and adaptive skills measurement for treatment planning, as these frame social-communication difficulties relative to overall developmental level 1

Mandatory Medical Workup

Audiologic Testing

Every child or adult with suspected ASD must have a formal audiogram to rule out hearing loss that could mimic ASD symptoms before proceeding with further evaluation. 1, 4 This is a critical step that cannot be skipped.

Genetic Evaluation

A genetic consultation should be offered to all persons/families with ASD, as thorough clinical genetics evaluation identifies an underlying etiology in 30-40% of individuals. 1, 4

Tiered Genetic Testing Approach

First-tier testing (order these for all patients):

• Chromosomal microarray (CMA): 10% diagnostic yield 1, 4
• Fragile X DNA testing: 1-5% yield 1, 4
• High-resolution karyotype: 3% yield 1, 4

Second-tier testing (based on specific clinical features):

• MECP2 gene testing in females: 4% yield 1, 4
• PTEN gene testing if head circumference >2.5 standard deviations above mean: 5% yield 1, 4

Additional testing only when clinically indicated:

• EEG for Landau-Kleffner syndrome when marked aphasia develops 1
• Neuroimaging, metabolic testing, or other genetic studies only when specific clinical features warrant them 1

Psychological Assessment

• Expect considerable scatter in intelligence test results, with possible "splinter skills" or savant abilities in specific domains 1
• Assess for areas of intense, circumscribed interests in higher-functioning individuals 1

Co-occurring Conditions Screening

Screen for psychiatric comorbidities, which are significantly more prevalent in ASD:

• Depression: 20% vs 7% in general population 4, 2
• Anxiety: 11% vs 5% 4, 2
• Sleep difficulties: 13% vs 5% 4, 2
• Epilepsy: 21% with co-occurring intellectual disability vs 0.8% 2

Critical Pitfalls to Avoid

• Do not delay diagnosis due to misconceptions about presentation, particularly in adults or atypical cases 3, 1

• Do not order extensive genetic testing without clinical geneticist evaluation first, as the stepwise approach with higher-tier tests is more cost-effective and better tolerated by families 1

• Do not skip the audiogram, as hearing loss can mimic ASD symptoms and must be ruled out 1, 4

• Do not fail to provide recurrence risk information to families: full sibling recurrence risk is 3-10% (7% if affected child is female, 4% if male), increasing to at least 30% with two or more affected children 1

Establishing Care Coordination

• Establish a primary care medical home for every individual with ASD to coordinate diagnostic testing and ongoing care 1
• Provide genetic counseling to all families regardless of whether an etiology is identified 1, 4
• Schedule periodic reevaluations for patients without a definitive etiology, as diagnostic technology continues to evolve 1