Large-scale Autism study reveals inaccuracies in screening tests

By Dr. Ananya Mandal, MDSep 27 2019

In one of the largest autism studies, some questions regarding diagnostic accuracy have been raised. The first study of its kind by the researchers at Children's Hospital of Philadelphia (CHOP) reveals that the most common screening tool used to detect autism spectrum disorder (ASD) among toddlers could be less than accurate. The study titled, “Accuracy of Autism Screening in a Large Pediatric Network,” was published in the latest issue of the journal Pediatrics.

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The study says that the American Academy of Paediatrics (AAP) has recommended screening all toddlers between 18 and 24 months age for autism using the Modified Checklist for Autism in Toddlers with Follow-Up (M-CHAT/F). This checklist is a two-stage parent survey. This screening system is completed with a follow-up system to eliminate the risk of overdiagnosis or false positives. False positives are those children who have been wrongly diagnosed with autism.

The researchers on this new large study reveal that most of the early studies that helped develop the AAP guidelines had been conducted in strict research settings rather than in real life. This means that there may be errors in the results which may not translate into the real world. The team wrote that there is little information on the long-term outcomes of the children who have been screened to be negative for autism on the M-CHAT/F.

This latest study looked at the effect of screening results in a primary care setting.  

As part of a large paediatric network implementing universal screening, we found ourselves in a unique position to find answers to critical questions about the accuracy of the M-CHAT, and to determine how many children are missed by early, universal screening. Early intervention has been shown to improve outcomes, potentially into adulthood. We know that early and accurate screening and diagnosis is the crucial first step in helping children access those effective, autism-specific therapies.”

Lead author Whitney Guthrie, clinical psychologist specializing in early diagnosis at CHOP's Center for Autism Research

For this study, the team looked at electronic health records (EHR) of 25,999 children with autism who had been screened at the primary healthcare setting between aged 16 and 26 months using the M-CHAT/F. These children were then followed up for four years between 4 and 8 years of age of each of the children using the health records. The results revealed that 91% percent of the children followed up had been screened using the standard M-CHAT/F. Of all the screenings, 40% of the children were detected with ASD. These children diagnosed with ASD had also been detected with the condition an average of seven months earlier than those children who had been declared negative at the screening. This meant that early screening helped early detection of ASD. Of the 40%, 2.2% of the children were found to be on the autism spectrum. This percentage is similar to the national average released by the Centers for Disease Control and Prevention (CDC).

Although our findings reveal significant shortcomings in current screening tools, we want to be clear that we are not recommending that paediatricians stop universal screening.”

Whitney Guthrie

Whitney Guthrie added, “Instead, clinicians should continue to screen using the M-CHAT/F, while being aware that this screening tool does miss some children with ASD. Any clinical or parental concerns should be taken seriously, and warrant continued surveillance even if a child screens negative on the M-CHAT/F. And of course, a screen positive on the M-CHAT/F warrants referral so that children with ASD can be diagnosed and receive early intervention. Paediatricians should also be aware of disparities in screening practices and results in children of colour and from low-income backgrounds.”

This new study also showed that 9% of the children who had not been screened between ages 18 and 24 months belonged to racial minority groups, from lower and medium-income households, from Medicaid receiving families and from non-English speaking families. These children, when screened using the M-CHAT, were found to be false positives.

Female children were less likely to be accurately diagnosed with ASD compared to males. Co-author of the study Kate Wallis, a developmental pediatrician and researcher at CHOP's Policy Lab explained, “Persistent racial and economic disparities in autism screening and diagnosis are a cause for great concern, and are consistent with previous research showing that black and Hispanic children tend to be diagnosed years later than white children.” She added, “This study revealed important limitations and provides us with new knowledge that we can use to make critical improvements to autism screening tools and screening processes, so paediatricians can properly detect and support more children with autism and reduce disparities in diagnosis and care.”