Diagnosis of Autism Spectrum Disorder: Clinical Criteria Only

Autism Spectrum Disorder (ASD) is a neurodevelopmental disorder that is diagnosed purely on clinical grounds. There is no laboratory test, imaging study, or genetic marker that can confirm or rule out the diagnosis. Diagnosis is made by a trained clinician based on developmental history and direct behavioral observation, using standardized diagnostic criteria such as the DSM-5 (persistent deficits in social communication/interaction plus restricted, repetitive patterns of behavior, interests, or activities present from early childhood) or ICD-11, often supplemented by standardized tools/checklists (e.g., CARS, ADOS, M-CHAT) that are themselves based on clinical observation.

Option-wise Analysis

• Clinical criteria and genetic studies only: Incorrect. Genetic testing (e.g., chromosomal microarray, fragile X testing) is sometimes recommended after a clinical diagnosis of ASD is made, mainly to look for an associated or causative genetic syndrome (found in only a minority of cases). It is not required for, nor does it establish, the diagnosis of ASD itself.
• Clinical criteria only: Correct. ASD is a behaviorally defined diagnosis. There is no blood test, brain scan, or genetic test that diagnoses autism — the diagnosis rests entirely on meeting standardized clinical/behavioral criteria based on history and observation.
• Clinical criteria and MRI brain only: Incorrect. MRI may occasionally be done to exclude other structural neurological causes in a child with developmental delay, but it has no diagnostic role in ASD — imaging findings are neither sensitive nor specific for autism.
• Clinical criteria, genetic studies and MRI brain: Incorrect for the same reasons above — both genetic testing and MRI are, at most, adjunctive investigations used to search for comorbid or causative conditions, not diagnostic tools for ASD.

Hence, the diagnosis of Autism Spectrum Disorder is based on clinical criteria only.