Diagnostic Process for Autism Spectrum Disorder (ASD)
The diagnosis of autism spectrum disorder requires a comprehensive multidisciplinary assessment by professionals trained in ASD diagnosis using objective criteria and standardized tools, with a tiered evaluation approach recommended for identifying potential genetic causes. 1
Initial Screening and Diagnosis
- Screening for ASD should be performed routinely during developmental assessments at 18 and 24 months of age using validated tools like the Modified Checklist for Autism in Toddlers (M-CHAT) 1, 2
- Common early signs in a child's first 2 years include no response to name when called, limited use of gestures in communication, and lack of imaginative play 3
- All children with suspected ASD must have a formal audiogram to rule out significant hearing loss that could mimic ASD symptoms 4, 1
- Diagnosis should be based on DSM-5 criteria, requiring deficits in social communication/interaction across multiple contexts and at least two restricted/repetitive behaviors 3, 5
- The diagnostic process should include direct observation of the child and structured caregiver interviews using standardized measures such as the Autism Diagnostic Observation Schedule-Second Edition (ADOS-2) 3
Recommended Diagnostic Tools
- Modified Checklist for Autism in Toddlers (M-CHAT) - recommended for children under 24 months with strong supporting evidence 2
- Autism Diagnostic Observation Schedule-Second Edition (ADOS-2) - has 91% sensitivity and 76% specificity 3
- Autism Diagnostic Interview - has 80% sensitivity and 72% specificity 3
- Screening Tool for Autism in Two-Year-Olds (STAT) - level 2 screener with sensitivity up to 92% and specificity up to 85% in 2-year-olds 2
Tiered Genetic Evaluation Approach
Pre-evaluation
- Confirmation of ASD diagnosis by trained professional using objective criteria and tools 4
- Complete audiogram for sensory screening 4
- Electroencephalogram if clinical suspicion of seizures exists 4
- Cognitive testing 4
- Verification of newborn screening results 4
First Tier Evaluation
- Physical examination with special attention to dysmorphic features (including Woods lamp evaluation) 4
- High-resolution chromosomal analysis 4
- DNA testing for Fragile X syndrome 4
- Metabolic screening if clinically indicated (urine mucopolysaccharides and organic acids, serum lactate, amino acids, ammonia, acyl-carnitine profile) 4
Second Tier Evaluation
- Chromosomal microarray (comparative genomic hybridization) 4, 2
- MECP2 gene testing (females only) 4
- PTEN gene testing (if head circumference is 2.5 SD greater than mean) 4
Third Tier Evaluation
Special Considerations
- Siblings of children with ASD have an elevated risk (14-18%) and require intensified surveillance 2
- Diagnostic stability of ASD is well established in children aged ≥24 months, though diagnosis before 24 months may have higher false-positive rates 2
- Individuals with ASD have higher rates of comorbidities including depression (20% vs 7%), anxiety (11% vs 5%), sleep difficulties (13% vs 5%), and epilepsy (21% with co-occurring intellectual disability) 3
- Autistic individuals have a 20-30 year lower life expectancy than non-autistic people 5
Common Pitfalls to Avoid
- Delaying diagnosis due to lack of awareness or societal stigma 6, 1
- Failing to rule out hearing loss which can mimic ASD symptoms 4
- Overlooking comorbid conditions that affect up to 75% of ASD patients 7
- Using the original CHAT screening tool which has low sensitivity (18%) 2
- Neglecting to provide genetic counseling and recurrence risk information to families 1
Using current knowledge and technology, a thorough clinical genetics evaluation of persons with ASDs will result in a positive etiologic diagnosis in up to 40% of individuals 4.