Intellectual Disability Diagnosis

Diagnostic Criteria

The American Academy of Child and Adolescent Psychiatry recommends diagnosing intellectual disability when both intellectual functioning (IQ ≤70) and adaptive functioning deficits across multiple domains are present, with onset during the developmental period before age 18 1, 2, 3
Intellectual functioning deficits are characterized by an IQ score ≤70 (approximately 2 SD below mean) on individually administered, standardized, culturally appropriate intelligence tests, as recommended by the American Academy of Child and Adolescent Psychiatry 1, 4
Adaptive functioning deficits must be significant and present across conceptual, social, and practical domains, according to the American Academy of Child and Adolescent Psychiatry 1, 5, 3
Severity classification is based on adaptive functioning, not IQ scores, as stated by the American Academy of Child and Adolescent Psychiatry 1, 3

For children under 5 years, the American Academy of Pediatrics suggests using "Global Developmental Delay" instead of intellectual disability, as IQ measures are unreliable in this age group, and requires significant limitations in ≥2 developmental domains 1, 2
For children 5 years and older, the American Academy of Child and Adolescent Psychiatry recommends using "Unspecified Intellectual Disability" when assessment is impossible due to sensory/physical impairments or severe communication difficulties 1, 2

The American Academy of Child and Adolescent Psychiatry advises ruling out specific learning disorders, communication disorders, autism spectrum disorder, major/mild neurocognitive disorders, and affective disorders or psychosis before confirming an intellectual disability diagnosis 5, 7

The American Academy of Child and Adolescent Psychiatry recommends using the Ages and Stages Questionnaire (ASQ-III) for screening developmental delay in children aged 1-66 months, with sensitivity 0.83-0.89 and specificity 0.80-0.92 2
The American Academy of Child and Adolescent Psychiatry suggests using the Developmental Behaviour Checklist (DBC), Nisonger Child Behavior Rating Form (NCBRF), and Reiss Screen for Children's Dual Diagnosis (RSCDD) for psychiatric comorbidity assessment 9

The American Academy of Child and Adolescent Psychiatry recommends screening for common comorbidities, such as epilepsy, autism spectrum disorder, ADHD, anxiety disorders, and oppositional defiant disorder, which occur at 3 times higher rates than in typically developing children 5, 7
The American Academy of Child and Adolescent Psychiatry advises providing individualized supports based on specific adaptive functioning deficits across conceptual, social, and practical domains 5, 6
The American Academy of Child and Adolescent Psychiatry suggests monitoring for psychiatric disorders using validated behavioral assessment tools, as psychiatric comorbidity is 3-fold higher 5, 7, 9

The American Academy of Child and Adolescent Psychiatry warns against relying solely on IQ scores for diagnosis or severity classification, as adaptive functioning determines severity 1, 3
The American Academy of Child and Adolescent Psychiatry advises against assuming static disability, as cognitive and adaptive skills can improve with early intervention, treatment of comorbidities, and environmental supports 5, 7
The American Academy of Child and Adolescent Psychiatry recommends considering cultural/linguistic factors, as standardized tests may underestimate abilities in minority populations 1, 4
The American Academy of Child and Adolescent Psychiatry suggests using structured behavioral assessment tools to identify psychiatric comorbidities, as self-report is unreliable in this population 9