Screening and surveillance for autism and pervasive developmental disorders

Screening and surveillance Screening and surveillance are diVerent but related activities involving the detection of impairments with a view to prevention or amelioration of consequent disability and handicap. Screening is the prospective identification of unrecognised disorder by the application of specific tests or examinations. Surveillance refers to the ongoing and systematic collection of data relevant to the identification of a disorder over time by an integrated health system. The review by Hall in Health for all children concluded that most screening tests that set out to identify neurodevelopmental disorders do not meet the stringent criteria outlined by Cochrane and Holland and Wilson and Jungner. In some conditions, for example language disorders, this is because there is uncertainty about “caseness” and tests tend to have low sensitivity and specificity. 5 This is particularly the case for screening tests that attempt to identify a specific condition rather than general developmental delay, and for the identification of relatively rare disorders. In the latter case, even when the sensitivity and specificity of a screen remain constant, the positive predictive value (the proportion of children with a positive screen result and who have the disorder) is lower the rarer a disorder is within the population. The concept of developmental surveillance is a parent–professional partnership that takes a broader look at developmental and behavioural skills and progress over time. It combines the observations of parents with the developmental knowledge of the professional and the deployment of specific tests. There is evidence that the use of screening instruments in combination with asking parents about their concerns improves the eYciency of an instrument. 8 However, the number and type of concerns that parents have about their child’s behaviour and development determine whether using a screening instrument within the clinic setting is eVective. For example, Glascoe, in a series of studies using the Parents’ Evaluations of Developmental Status (PEDS), has shown that when parents had a single significant concern about their child’s development (or there was a communication barrier because parents did not share the same first language as the paediatrician) the use of a screening test increased the specificity of onward referral at only a slight cost to sensitivity. However, when parents had two or more concerns about their child’s development (for example, self help, social, or receptive language diYculties), use of additional screens led to an unacceptable drop in sensitivity, indicating that onward referral for diagnostic evaluations is the best course of action in such cases. Despite the challenges of screening for neurodevelopmental disorders, there is professional and public agreement that early identification of child health problems is desirable. Notably this includes identification of developmental disabilities as well as medical diseases. 12 Further, over the last decade the emphasis has shifted from screening in the preschool years, to infants from birth to 2 years of age.