Overview of Population-Based ASD Screening Studies in Europe: 20 Years After CHAT

Background: Great efforts have been put into developing methods for early identification of toddlers with autism spectrum disorder (ASD) across Europe since the Checklist for Autism in Toddlers (CHAT) was first developed in 1992. Many studies have used similar screening instruments. The administration of them, however, differs considerably.. A group of researchers involved in population-based ASD screening studies in Europe have gathered in order to collaborate and interchange experiences in this area.  This group is part of COST action grant: “Enhancing the scientific study of early autism: A network to improve research, services and outcomes (ESSEA: www.cost-essea.com)”. Objectives: The first aim of this study is to provide a systematic overview of the different screening procedures and the corresponding validity measures for early identification of ASD used in all the population-based studies across Europe with the Checklist for Autism in Toddlers (CHAT), the Modified Checklist for Autism in Toddlers (M-CHAT), the Early Screening of Autistic Traits (ESAT), the Checklist for Early Signs of Developmental Disorders (CESDD), the Social Communication Questionnaire (SCQ), and the Communication and Symbolic Behavior-Scales-Developmental Profile-Infant Toddler Checklist (CSBS-DP-ITC). A second aim will be to describe the challenges regarding early screening by extracting data from this overview. Methods: MEDLINE and PsychINFO were used to find published ASD screening studies. Only population-based screening studies conducted in Europe were selected. And investigated. Additional information not available in the articles and some unpublished data was gathered by approaching the main researchers through the COST-ESSEA network. Information from each study were either extracted from the article or calculated from gathered data . The resulting material was tabulated to make the data comparable and to extract the most important issues regarding early screening methods. Results: The administration and outcomes of the screening instruments vary on several aspects. While some screening tools are the same across studies, they are administered in combination with a different surveillance or first screening approach, subsequently influencing validity measures. Furthermore, ages at screening and during diagnostic procedures, and the time between assessments, vary across studies. This also affects sensitivity and specificity. At a very young age it might be hard to differentiate between ASD and other developmental disorders, and signs of ASD might be too subtle to recognize. Population screening at 14 months results in low sensitivity and many false positives. Studies are also not alike in the setting and procedures of the screeners. Conclusions: The screening procedures for the early identification of ASD across Europe differ on many aspects, including surveillance ages, procedures and setting. This affects the validity measures of those instruments and the identification of ASD. Since screening instruments for ASD are administered in varied ways it is valuable both for clinical and research purposes to have some kind of overview in which different methods are compared. Although it is impossible to draw firm conclusions as to which screening method is most effective, the overview and the issues raised may help future implementation of screening methods and thereby improve the early identification of ASD.