DSM-IV Criteria

Diagnosing autism is not a precise affair. There is not a blood test or trademark symptom that can be relied upon as proof positive of the diagnosis. Instead the patient’s symptoms are compared to a range diagnostic criteria and the doctor makes a judgment call. This might be one explanation for the apparent increase in autistic children. As doctors have become more aware of the condition, they are more likely to match a child’s symptoms with the diagnostic criteria of autism rather than marking them down as mentally retarded. See Autism Epidemic! What Autism Epidemic?.
The criteria used in the USA is the Diagnostic and Statistical Manual of Mental Disorders, currently in its fourth version, and generally known by its short hand of DSM-IV. It defines autism as:

DSM-IV Criteria, Pervasive Developmental Disorders. 299.00 Autistic Disorder

A. A total of six (or more) items from (1), (2), and (3), with at least two from (1), and one each from (2) and (3):

  • (1) qualitative impairment in social interaction, as manifested by at least two of the following:
    • (a) marked impairment in the use of multiple nonverbal behaviors, such as eye-to- eye gaze, facial expression, body postures, and gestures to regulate social interaction
    • (b) failure to develop peer relationships appropriate to developmental level
    • (c) a lack of spontaneous seeking to share enjoyment, interests, or achievements with other people (e.g., by a lack of showing, bringing, or pointing out objects of interest)
    • (d) lack of social or emotional reciprocity
  • (2) qualitative impairments in communication, as manifested by at least one of the following:
    • (a) delay in, or total lack of, the development of spoken language (not accompanied by an attempt to compensate through alternative modes of communication such as gesture or mime)
    • (b) in individuals with adequate speech, marked impairment in the ability to initiate or sustain a conversation with others
    • (c) stereotyped and repetitive use of language or idiosyncratic language
    • (d) lack of varied, spontaneous make-believe play or social imitative play appropriate to developmental level
  • (3) restricted, repetitive, and stereotyped patterns of behavior, interests, and activities as manifested by at least one of the following:
    • (a) encompassing preoccupation with one or more stereotyped and restricted patterns of interest that is abnormal either in intensity or focus
    • (b) apparently inflexible adherence to specific, nonfunctional routines or rituals
    • (c) stereotyped and repetitive motor mannerisms (e.g., hand or finger flapping or twisting or complex whole-body movements)
    • (d) persistent precoccupation with parts of objects

B. Delays or abnormal functioning in at least one of the following areas, with onset prior to age 3 years:

  • (1) social interaction
  • (2) language as used in social communication
  • (3) symbolic or imaginative play.

C. The disturbance is not better accounted for by Rett’s disorder or childhood disintegrative disorder.