Sensitivity of toddler screening: Integrating concurrent and prospective strategies to detect ASD - Screening for autism spectrum disorder (ASD) during well-child pediatric check-ups reduces the age of diagnosis, allowing more time for critical early intervention. Furthermore, universal screening mitigates disparities in the age of diagnosis for minorities, and has been demonstrated to be feasible in community- based primary care settings. However, limited follow-up of toddlers who screened negative is a notable gap in the literature that contributed to the United States Preventive Services Task Force’s (USPSTF) determination of insufficient evidence to recommend universal ASD screening at present. Follow-up of children who are not identified at risk is cost- and labor-intensive, but is critical to determine the sensitivity of toddler ASD screening. This study will be among the first to use rigorous prospective detection strategies in a large, low-risk sample that previously had concurrent detection. The goal of the proposed study is to find missed cases by rescreening children who were not identified with ASD during the course of three prior screening studies that administered the Modified Checklist for Autism in Toddlers, Revised, with Follow-Up during toddler well child visits. This includes those who screened negative as toddlers, as well as children who screened positive but either were lost to follow-up or were evaluated and not diagnosed with ASD. The specific aims are to measure prospective sensitivity using rigorous case confirmation for potential missed cases. We will identify patterns in toddler screening outcomes for these missed cases; we predict that children whose first screen was younger and those who did not complete multiple screens are more likely to be missed cases compared to those screened at older toddler visits and rescreened by age three. Finally, we will examine whether missed cases are more likely to have milder ASD symptoms, greater likelihood of psychiatric comorbidities, and be female compared to children who demonstrated risk as toddlers but were not diagnosed with ASD until they were older. Although these characteristics have been hypothesized, rigorous evidence is lacking to demonstrate differences between children with ASD missed by toddler screening. The majority of the multi-site sample (total n = 8,751) screened negative at one or more pediatric visits between 1 and 3 years old (n = 8,091). In addition, we will rescreen children who screened positive but did not attend the evaluation (n = 426), which often signals lack of parent concern, and children evaluated and classified as nonASD (n = 234), who may have developed clinically significant ASD symptoms as they aged. Parents will be invited to enroll and rescreen their child, now 7-14 years old, using a secure web-based portal. All at risk children, and a random sample of low-risk cases, will be invited for a comprehensive, research-reliable evaluation; final ASD outcomes will be used to calculate prospective sensitivity, which will be compared to literature reporting sensitivity based on record review strategies. Results of this proposed study will directly address a gap identified by the USPSTF, and will address the Interagency Autism Coordinating Committee’s Question 1 about early detection of ASD.