Question: Are there certain tests that should be given to evaluate autism, and are there blood tests or some other way to be certain of a correct diagnosis?
Answer: Autism is a clinical diagnosis. It should fulfill the core criteria within the DSM-IV, which is the manual that delineates the clinical criteria and socialization, communication and repetitive behaviors restricted interests. There are some assessment tools such as the ADI (Autism Diagnosis Interview) and the ADOS (Autism Diagnostic Intervention Schedule) that can be used to help confirm people's clinical impressions or to help in clinically difficult cases that are there. But ultimately it's basically done by people who have the expertise to make the decision.
Blood tests do not diagnose autism. Blood tests may sometimes identify the reason for autism, the genetic reason or some sort of biochemical disturbance that may be associated.