ASD Diagnostic Assessment – CPS Position Statement Notes (2019)

Overview and context

  • Rising prevalence of autism spectrum disorder (ASD) creates a need to expand diagnostic capacity among community-based pediatricians and primary care providers.
  • Although some children can be definitively diagnosed by age 2, many are not diagnosed until 4–5 years of age.
  • Multidisciplinary team involvement is commonly recommended in guidelines.
  • Recommended wait times for ASD diagnostic evaluation range up to 3–6 months in some guidelines, but in many Canadian communities the wait from referral to evaluation exceeds 12 months.
  • Goal of the statement: provide community-based clinicians with recommendations, tools, and resources to perform or assist in ASD diagnostic evaluation; offer guidance on referrals for comprehensive needs assessment for treatment and intervention planning; promote a flexible, multilevel approach.
  • Key implications: need for more trained pediatric health care providers to diagnose less complex cases; balance between access to services and diagnostic certainty; emphasis on family-centered care and culturally competent practices.

Who should conduct the ASD diagnostic assessment?

  • In most provinces/territories, ASD can be diagnosed by physicians or psychologists; some communities allow appropriately trained nurse practitioners to diagnose ASD.
  • Emerging evidence suggests a trained sole practitioner can diagnose less complex ASD cases, but most guidance documents still favor a team-based approach led by a primary care provider, pediatric specialist, or clinical child psychologist trained in ASD.
  • Practical implication: even when a sole practitioner can diagnose, access to specialized services may require additional input or referral.

Approaches toward an ASD diagnostic evaluation

  • Three approaches are proposed, chosen based on the clinician’s experience, symptom complexity, and psychosocial history.
  • Regardless of approach, maintain open communication, collaboration, and consent to share information to improve diagnostic accuracy and avoid duplication.

Approach 1: Sole paediatric care provider diagnosis

  • When symptoms clearly indicate ASD, an experienced or trained sole pediatric care provider can independently diagnose ASD using clinical judgement and DSM-5 criteria, with or without data from a diagnostic assessment tool.
  • This approach may not suffice for accessing specialized services in some jurisdictions.
  • May involve a diagnostic assessment tool, e.g., as part of the evaluation.
  • Suitable when presentation is straightforward and local services do not require a team-based diagnosis for access to supports.

Approach 2: Shared care model

  • Clinician shares responsibility with another health care provider for patient care; information exchange and clinical knowledge sharing occur.
  • Used when the child’s symptom presentation is milder, atypical, or complex, or when the child is under 2 years of age.
  • Clinician may use information from a diagnostic tool and consult with another professional with specialized knowledge (e.g., a psychologist) to inform the diagnosis.
  • Balances local primary care with specialist input to enhance diagnostic accuracy without full team collaboration.

Approach 3: Team-based approach

  • Diagnostic assessment performed by health care professionals in an interdisciplinary or multidisciplinary team.
  • Interdisciplinary teams work collaboratively in an integrated, coordinated fashion; multidisciplinary teams work independently but share information and may reach a consensus.
  • In some jurisdictions, only a team-based approach is accepted for accessing specialized services.
  • A community clinician may refer to an ASD diagnostic team when presentation is subtle, complicated by co-existing health concerns, or a child has a complex medical/psychosocial history.
  • Pros: can improve diagnostic certainty and inform comprehensive treatment planning; cons: may prolong wait times in some settings.
  • Note: Delays can be a barrier to early interventions, especially in areas with limited access to specialized services; multidisciplinary evaluations can also support treatment planning and access to supportive programs.

Purpose and essential components of an ASD diagnostic assessment

  • There are no diagnostic biomarkers for ASD; diagnosis is clinical, based on detailed history, physical examination, and observation of characteristic behaviors.
  • Consensus does not set a universal maximal wait time; some guidelines recommend a 3–6 month interval from referral to assessment, while others do not specify a maximum.
  • Expedited assessments can facilitate earlier access to educational interventions and community-based services.

The three key objectives of the ASD diagnostic assessment

1) Provide a definitive (categorical) diagnosis of ASD.

  • In ambiguous or milder cases (e.g., under 2 years of age), provisional diagnosis may be made with careful monitoring and referral for in-depth evaluation.

  • In many jurisdictions, specialized ASD interventions may not be available for children with a provisional diagnosis.
    2) Explore conditions that mimic ASD and identify co-occurring conditions.
    3) Determine the child’s overall level of adaptive functioning to aid intervention planning, including strengths, challenges, and personal interests.

  • The family-centered approach is essential: clinicians must listen to and engage with parents and family members; consider family history, cultural and religious values, and potential barriers to care (e.g., socio-economic adversity).

  • When language is a barrier, interpreters are essential for culturally competent care.

  • An algorithmic view (Figure 1) outlines the diagnostic process and its components.

Stepwise ASD diagnostic assessment (Steps 1–8)

Step 1: Records review

  • Begin with reviewing prior records and interviewing parents/caregivers about concerns.
  • Developmental history and planning for direct observation/assessment.

Medical records to review include:

  • Birth records, newborn screening results
  • Routine well-child visits, early concerns
  • Medical tests, prior treatments, medications
  • Specialist evaluations, hospitalizations

Other records to review include:

  • Developmental evaluations (ASD screening), other assessments (hearing, vision, speech-language, psychological, behavioral, occupational therapy)
  • Other care provider information (child care staff, teachers)
  • Educational records when available

Step 2: Interviewing parents, family members, or other caregivers

  • Use semi-structured, open-ended questions; may be integrated with standardized questionnaires.
  • Topics include: reasons for referral and onset of concerns; pregnancy, birth, labor; developmental history; current functioning and behaviors; medical history (sleep, diet, self-injury); early intervention/education history; family medical/mental health history and genetic conditions; psychosocial history (violence, trauma, substance use, neglect); family functioning, routines, resources; anticipated reactions to diagnosis and family goals.

Step 3: Assessment for core features of ASD

  • Observe and interact with the child to assess social interaction and communication abilities; evaluate patterns of behavior/interests with focus on DSM-5 criteria.
  • Behavioral observation in multiple settings is ideal (clinic, home, child care); many assessments occur in clinical settings.
  • An ASD-specific diagnostic tool may be used.
  • Two broad categories of ASD diagnostic tools:
    • Observational/interaction-based tools (e.g., ADOS-2, CARS-2)
    • Interview/questionnaire-based tools (e.g., ADI-R, SRS-2)
  • Findings from diagnostic tools should complement, not replace, clinical judgement.
  • Clinically useful tools typically have sensitivity and specificity of at least 80%; table 1 summarizes age-specific tools.
  • The latest Cochrane review suggests that for preschoolers, ADOS has high sensitivity and comparable specificity to CARS and ADI-R; in some jurisdictions, ADOS and ADI-R are required for diagnosis.

Step 4: Comprehensive physical examination and additional investigations

  • Physical exam aims to rule out medical causes and guide treatment planning.

  • Components include: height/weight, head circumference (noting that ~20% of individuals with ASD have macrocephaly), skin exam for signs of neurocutaneous syndromes, neurological exam, dysmorphic features, hearing/vision assessments, and targeted investigations as clinically indicated.

  • Additional investigations may include:

    • EEG (seizures)
    • MRI (microcephaly, seizures, abnormal neuro exam)
    • Metabolic testing (developmental regression, seizures, lethargy with illness)
    • Chromosomal microarray (first-tier test for developmental disability, dysmorphic features, or congenital anomalies)
    • Blood lead levels in high-risk environments (developmental delay or pica)

  • Note: Evidence supports offering chromosomal microarray as a first-tier test in relevant cases.

Step 5: Consider differential diagnoses and co-occurring conditions

  • Consider other disorders that can overlap with or mimic ASD.
  • Table 2 lists common differential diagnoses and co-occurring conditions across several domains:
    • Neurodevelopmental disorders (e.g., ADHD, global developmental delay/intellectual disability, language/learning disorders, social (pragmatic) communication disorder, stereotypic movement disorder, tic disorders)
    • Mental/Behavioral disorders (e.g., anxiety, conduct, depressive disorders, disruptive mood dysregulation, OCD, oppositional defiant disorder, reactive attachment disorder, schizophrenia, selective mutism)
    • Genetic conditions (e.g., Fragile X, Rett syndrome, other genetic variants like 16p11 deletion, etc.)
    • Neurological/medical conditions (e.g., cerebral palsy, epilepsy, Landau-Kleffner syndrome, mitochondrial disorders, neonatal encephalopathy)
  • Important note: Social (pragmatic) communication disorder is mutually exclusive with ASD.

Step 6: Establishing an ASD diagnosis

  • A trained clinician uses DSM-5 criteria together with clinical judgment to differentiate ASD from other developmental disorders.
  • See DSM-5 criteria in the companion resources; formal DSM-5 criteria summary is referenced in the material.

Step 7: Communicating ASD diagnostic assessment findings

  • Ideal: a face-to-face feedback session with both parents and the child (as appropriate), in the family’s primary language; interpreters used when needed.
  • If in-person is not possible, use telephone/video-conferencing; ensure the session is handled sensitively and that parents have time to process information and ask questions.
  • Feedback should be provided verbally and in a written report suitable for a lay audience.
  • Report components to include:
    • Clear statement confirming whether the child meets DSM-5 ASD criteria (or not).
    • Reasons for referral and relevant developmental/family history.
    • Summary of pre-evaluation results and reviewed records.
    • Summary from family interview and direct observations that support the diagnosis.
    • Description of diagnostic tools used and the clinicians who conducted the evaluation.
    • How presenting symptoms meet DSM-5 criteria.
    • Co-occurring or suspected conditions identified or requiring further investigation.
    • Current functioning levels and recommended supports, with individualized referrals and intervention recommendations.
    • Recommendations for additional assessments if needed and parent resources.
    • Follow-up plan.
  • Sharing: provide the written report to the family, referring physician, other health professionals involved, and educational professionals with appropriate consent.
  • If a categorical ASD diagnosis cannot be determined at the time of assessment, consider gathering more information, observing in additional settings (home, child care), obtaining a second opinion, or repeating the assessment after therapy initiation or school entry.
  • If concerns do not meet ASD criteria, refer for further assessment addressing those concerns and services.

Step 8: Comprehensive assessment for intervention planning

  • After diagnosis, ensure a comprehensive needs assessment is considered for treatment planning if not included in initial evaluation.
  • The need for this assessment may recur across development and often occurs within educational or treatment programs.
  • The needs assessment should cover: cognitive/academic functioning; speech, language, and communication; sensory and motor functioning and sensitivities; adaptive functioning (e.g., self-help); behavioral and emotional functioning (anxiety, self-esteem); physical health and nutrition.
  • The extent of assessment for intervention planning depends on the approach used for the initial diagnostic evaluation:
    • Approach 1 (sole clinician): may require referral to an interdisciplinary team for a comprehensive needs assessment, especially if intervention planning occurs outside school/treatment contexts.
    • Approach 2 (shared care): may provide additional information for intervention planning (e.g., cognitive functioning); further referrals for sensory/motor areas if indicated.
    • Approach 3 (team): diagnostic evaluation and intervention planning are more likely to occur concurrently; additional assessments may or may not be necessary.

Common ASD diagnostic tools (Table 1)

  • Diagnostic tools fall into two categories: observational/direct interaction-based tools and informant/parent interview or questionnaire tools.
  • General requirement: tools should contribute to diagnostic decision, complement clinical judgement, and have acceptable sensitivity and specificity (≥80%).
  • Examples and key data:
    • Autism Diagnostic Observation Schedule – 2nd edition (ADOS-2)
    • Age group: 12 ext{ months to adult}
    • Time for completion: 45-60 ext{ minutes}
    • Test performance: Se = 92-100 ext{%}, Sp = 61-65 ext{%}, PPV = 80-84 ext{%}, NPV = 81-100 ext{%}
    • Test sample: ASD and non-ASD patients; clinical sampling
    • Comments: Behavioral observation of social interaction, play, communication, behaviors, interests
    • Childhood Autism Rating Scale – 2nd edition (CARS-2)
    • Age: 2+ ext{ years}
    • Time: 20-30 ext{ minutes}
    • Se = 89-94 ext{%}, Sp = 61-100 ext{%}, PPV = 71-100 ext{%}, NPV = 46-56 ext{%}
    • Snapshot: Clinically referred children
    • Autism Diagnostic Interview- Revised (ADI-R)
    • Age: 2 ext{ years to adult}
    • Time: 1.5-3 ext{ hours}
    • Se = 53-90 ext{%}, Sp = 67-94 ext{%}, PPV = 82-98 ext{%}, NPV = 26-68 ext{%}
    • Sample: Clinically referred; high to low risk for ASD
    • Comments: Social interaction, communication, behaviors and interests; mostly used for research
    • Social Responsiveness Scale – 2nd edition (SRS-2); preschool and school-aged versions
    • Age: 2.5-4.5 ext{ years}; 4-18 ext{ years}
    • Time: 15-20 ext{ minutes}
    • Se = 75-78 ext{%}, Sp = 67-94 ext{%}, PPV = 93 ext{%}
    • Sample: 442 children with or without ASD
    • Diagnostic Interview for Social and Communication Disorders (DISCO)
    • Age: Any age
    • Time: Up to 3 ext{ hours}
    • Se = 96 ext{%}, Sp = 79 ext{%}
    • Sample: Children with different levels of ID; detailed, semi-structured interview with a dimensional approach; mostly used for research
    • Developmental, Dimensional and Diagnostic Interview (3di) (computerized)
    • Age: 3+ ext{ years}
    • Time: Up to 2 ext{ hours}
    • Se = 84-100 ext{%}, Sp = 54-98 ext{%}
    • Sample: Children with or without ASD; 740 items
  • Notes:
    • Training is required to use all tools except SRS-2.
    • ASD = Autism spectrum disorder; ID = Intellectual disability; NPV = Negative predictive value; PPV = Positive predictive value; Se = Sensitivity; Sp = Specificity.

Differential diagnoses and co-occurring conditions (Table 2)

  • The assessment should consider a broad differential to avoid misdiagnosis and to identify co-occurring conditions.
  • Common categories and examples:
    • Neurodevelopmental disorders: ADHD, Global developmental delay or intellectual disability, Language or learning disorders, Social (pragmatic) communication disorder, Stereotypic movement disorder, Tic disorders (e.g., Tourette’s).
    • Mental/Behavioral disorders: Anxiety disorders, Conduct disorders, Depressive disorders, Disruptive mood dysregulation disorder, OCD, ODD, Reactive attachment disorder, Schizophrenia, Selective mutism.
    • Genetic conditions: Fragile X syndrome, Rett syndrome, Other genetic variants (e.g., 16p11 deletion).
    • Neurological and other medical conditions: Cerebral palsy, Epilepsy, Landau-Kleffner syndrome, Mitochondrial disorders, Neonatal encephalopathy.
  • Important relationship: Social (pragmatic) communication disorder is mutually exclusive with ASD.

Communicating diagnostic findings and sharing reports

  • Provide a clear, direct statement about whether the child meets DSM-5 criteria for ASD (e.g., "[Child’s name] meets DSM-5 criteria for a diagnosis of ASD"); avoid hedging language.
  • Include: reasons for referral, relevant developmental and family history, summary of pre-evaluation results, interviews, observations, tools used, how symptoms meet DSM-5 criteria, co-occurring conditions, current functioning, and intervention recommendations.
  • Include: referrals for services, additional assessments if needed, resources for parents, and a follow-up plan.
  • Written report should be shared with the family, referring physician, other health care providers, and educational professionals involved in care, with appropriate consents.
  • When a categorical ASD diagnosis is unclear, consider additional information gathering, setting changes, second opinions from ASD specialists, or repeating assessments at a later time.
  • If concerns do not meet ASD criteria, refer for further assessment and services addressing those concerns.

Comprehensive assessment for intervention planning

  • After a confirmed ASD diagnosis, the clinician should ensure a comprehensive needs assessment for treatment and intervention planning is considered if not already included in the diagnostic process.
  • This needs assessment may be revisited as the child develops and often occurs within education or treatment programs.
  • Areas evaluated may include:
    • Cognitive and academic functioning
    • Speech, language, and communication skills
    • Sensory and motor functioning, and sensory sensitivities
    • Adaptive functioning (e.g., self-help skills)
    • Behavioral and emotional functioning (e.g., anxiety, self-esteem)
    • Physical health and nutrition
  • Influence of diagnostic approach on needs assessment:
    • Approach 1 (sole clinician): may require referral to an interdisciplinary team for a comprehensive needs assessment, particularly if planning happens outside school/treatment contexts.
    • Approach 2 (shared care): can provide additional information for intervention planning (e.g., cognitive functioning); further referrals for other areas (sensory/motor) if indicated.
    • Approach 3 (multidisciplinary team): intervention planning often occurs concurrently with diagnostic evaluation; additional assessments may or may not be necessary.

Age, sex, culture, and geography considerations

  • Age: A definitive diagnosis is possible in children under 2, but challenging; younger cases require timely follow-up; development can alter symptom presentation over time.
  • Sex: ASD is diagnosed more often in boys than girls (approx. 4:1; among younger siblings, ~3:1). Girls may camouflage symptoms and be under-diagnosed; clinicians should be vigilant for sex/gender differences in presentation.
  • Culture and language: Minority groups may be diagnosed later; factors include access to services, interpretation of symptoms, and health system factors. Cultural factors influence understanding and help-seeking behaviors; interpreters are essential for culturally competent care.
  • Rural/remote regions: Diagnosis often occurs later; telehealth and itinerant developmental clinics can facilitate access; capacity-building in underserved areas is a priority.

Next steps after a confirmed ASD diagnosis

  • The community-based pediatrician or primary care provider plays a vital role in ongoing care: routine health maintenance, management of co-occurring medical conditions, and coordination among medical, educational, community, and social services.
  • For more information on condition management, refer to the companion statement in this issue and online resources.

Funding and conflicts of interest

  • Funding: Production of these guidelines was supported by the Public Health Agency of Canada; views expressed do not necessarily reflect the Agency.
  • Potential conflicts of interest: Authors report various disclosures; editors note that conflicts relevant to the content have been disclosed.

References and resources (context)

  • The document cites multiple national and international guidelines and studies (e.g., American Academy of Pediatrics guidance on identification and evaluation, NICE guidelines, Cochrane reviews, and other autism guideline bodies) to support diagnostic approaches, tool validity, and practice standards.
  • Core sources include DSM-5 criteria, ADHD and related neurodevelopmental considerations, and chromosomal microarray recommendations for developmental disorders.

Key takeaways

  • ASD diagnosis is clinical and relies on history, examination, and observation; there are no biomarkers.
  • Three practical diagnostic approaches exist (sole clinician, shared care, team-based); the choice depends on symptom complexity and local service access.
  • A structured, stepwise assessment (records, parent interview, core-feature assessment, physical exam, differential diagnosis, DSM-5 diagnosis, communication of findings, and intervention planning) is recommended.
  • Diagnostic tools (ADOS-2, CARS-2, ADI-R, SRS-2, DISCO, 3di) support but do not replace clinical judgement; use requires training (except SRS-2).
  • Consider differential diagnoses and co-occurring conditions; plan for comprehensive intervention planning when needed.
  • Communicate findings clearly to families, provide written reports, and ensure accessibility via language and cultural considerations; leverage telehealth and outreach to reduce access gaps in rural/remote areas.
  • After diagnosis, coordinate multidisciplinary supports, educational planning, and ongoing family-centered care, with attention to barriers and resources for families.