There are simple screening tests that can be used in growth and development checkups in primary care between 18 and 24 months of age. One of these tests is the M-CHAT and its more recent version, the M-CHAT-R/F . This is a screening test, not a diagnostic one, that indicates the risk of autism spectrum disorder (ASD). This means that a positive result indicates the need for further observation and evaluation, but does not necessarily constitute a diagnosis of autism spectrum disorder.