Factors Associated with Age of Diagnosis among Medicaid-Enrolled Children with Autism Spectrum Disorders in the United States

Background: Early diagnosis of autism spectrum disorders (ASD) is critically important, in large part because a growing body of evidence suggests that earlier intervention results in better outcomes. Despite the fact that autistic disorder can be diagnosed reliably by experienced clinicians in children as young as 24 months, studies suggest that the average age of diagnosis often is not until children are between 3 and 6 years of age, and varies as a function of families’ socio-demographic characteristics. While prior studies provided important information both on estimates and correlates of age of diagnosis, interpretation is limited because they relied on survey strategies subject to selection bias or were limited to small geographic areas. The current study builds on previous research by using a national dataset and includes information about child characteristics, state policies, and county resources that may affect age of diagnosis.

Objectives: to estimate the association between child, county and state characteristics and age of ASD diagnosis among Medicaid-enrolled children

Methods: Medicaid enrollment and claims data for all 50 US states and the District of Columbia from 2001-04 were linked with county-level data from the Area Resource File and the National Center for Education Statistics, which provided information on education and healthcare resources. The sample included all Medicaid-enrolled children age <9 years who 1) had a Medicaid claim associated with an ASD diagnosis (ICD-10 code 299.xx) between July 1, 2001 December 31, 2004; and 2) did not have any claim associated with an ASD diagnosis in the 6 months prior. Linear regression with random effects was used to estimate the effect of child, county and state characteristics on age of diagnosis.

Results: There were 74,512 Medicaid-enrolled children <9 years of age with a first diagnosis of ASD during the study period. The average age of diagnosis for the entire sample was 5.2 (SD = 1.4) years, was similar for those with an autistic disorder (299.0) diagnosis (5.1, SD = 1.5), and varied considerably by state and by county within states. Ongoing analyses suggest the important contribution of county medical and school resources and state policies that govern funding for autism treatment services.

Conclusions: To our knowledge, this is the first national study of correlates of age of diagnosis among children with ASD. Limitations include concerns about the validity of diagnosis in community settings, the generalizability of the findings to non-Medicaid-enrolled children, and the inability to distinguish between PDD-NOS and Asperger’s disorder in our data. Still, Medicaid serves 1 in 4 children in the US; the results suggest that ASD is diagnosed much later than is optimal among these children, and that socio-demographic characteristics as well as local healthcare resources and state policies contribute to disparities in age of diagnosis.