How would a child have medical tests for autism?

There are none: Autism is a clinical diagnosis made by a physician with experience of the disease. Every child has a different biochemical underlylng cause and where the research is focused.

Medical causes?: Medical evaluation is done in a child with autism to try to find the cause: thorough physical exam, measure head, ears, eyes and more, look for major or minor unusual features, skin pigmentation. Complete neurological exam. Assess all areas of development. Genetic microarray & dna probe for fragile x on all; other labs if needed. Mri of brain, eeg if warranted by history or neurological findings.

Blood tests: There are blood tests for some disorders that can look like autism, chromosome tests for fragile X, Retts syndrome and other genetic disorders. There is no medical test for autism. The diagnosis is made on behavioral features