Objective: This study examined child- and county-level factors associated with age of diagnosis of autism among Medicaid-enrolled children and the change in age of diagnosis over time.
Methods: National Medicaid claims from 2002 to 2004 were used to identify age of diagnosis and characteristics of children younger than ten years old with a diagnosis of autism (ICD-9 codes 299, 299.0x, or 299.8x). These data were linked to county-level education and health care variables. Linear regression with random effects for state and county was used to examine associations between these variables and age of diagnosis.
Results: A total of 28,722 Medicaid-enrolled children newly diagnosed with an autism spectrum disorder were identified. Their average age of diagnosis was 64.9 months. Adjusted average age of diagnosis dropped 5.0 months for autistic disorder and 1.8 months for other spectrum disorders during the study period. Asian children were diagnosed earlier than children in other racial or ethnic groups, although these differences were much more pronounced for other spectrum disorders than for autistic disorder. Children eligible for Medicaid through the poverty category were diagnosed earlier, on average, than children who were eligible through disability, foster care, or other reasons, although this difference decreased over time. Children in large urban or rural counties were diagnosed later than children in small urban or suburban counties.
Conclusions: Findings showed that diagnosis of autism occurs much later than it should among Medicaid-enrolled children, although timeliness is improving over time. Analyses suggest that most of the observed variation is accounted for by child-level variables, rather than county-level resources or state policies.