As the biomarker of autism is not yet known, the diagnosis is based on a careful evaluation of the medical history and objective observation of the child.
Research is intensively focused on the discovery of the first specific symptoms of ASD in child behavior, in order to develop a sensitive screening tool that can be used at the youngest possible age.
It is in the best interests of the child and his or her family, not to unnecessarily prolong the time between the first suspicion and the diagnosis. There is a long period of time between the age when parents first became concerned about their child’s atypical development and the age at which the diagnosis was made definitively. According to Chawarska et al. (2007) the first concern occurs on average around the 19 months of age of the child, 30% of parents observe abnormalities as early as the first year of life and about 80% within two years of a child’s life.
According to Zwaigenbaum et al. (2013) it is only possible to truly and well distinguish children with ASD from children with delayed development at two years of age. Given the diversity of disease manifestations, however, it is necessary to take into account that there are children who can be suspected and diagnosed already at one year of age. In contrast, about 25% to 30% of children, according to a retrospective assessment by their parents, develop normally and only within 15 to 24 months of age can there be a regression in development and the child manifests the disease (Johnson & Myers, 2007).