Performance of M-CHAT and ITC Screeners in High-Risk Siblings

Background:  It is important to examine screening efficacy in determining children at risk for ASD. Most studies have included low-risk toddlers; younger siblings of children diagnosed with ASD are a high-risk population of particular interest, given their elevated ASD prevalence of 1 in 5.4 (Ozonoff et al, 2011) compared to the general population’s prevalence of 1 in 68 (CDC, 2014).  

Objectives:  To examine two screening tools, the Infant-Toddler Checklist (ITC) and the Modified Checklist for Autism in Toddlers (M-CHAT), and to examine concordance between screening outcomes and ASD classification at 36 months. 

Methods:  Parents of high risk siblings (n=166; 74 females, 92 males) completed the ITC at 6, 12, and/or 18 months and/or the M-CHAT at 18 and/or 24 months. Sensitivity, specificity, and positive likelihood ratios were examined for each screener at each timepoint, combinations of timepoints for each screener, and both screeners at 18 months using clinical best estimate for classification.

Results:  As children got older, the percent who screened positive on each tool decreased (37.9%, 25.5%, and 22.4% for ITC, 25.8% and 21.6% for M-CHAT). The ITC sensitivity ranges from 48.5-69.2% and specificity from 65.2-91.1% for ages 6-18 months. The M-CHAT sensitivity ranges from 53.8-62.1% and specificity from 81.9-92.7% for ages 18-24 months. Sensitivity for ITC at any age from 6-18 months is 83.9% and for M-CHAT from 18-24 months is 82.1%. At 18 months, screening positive on one or both screens yielded 71.4% sensitivity and 76.4% specificity, while screening positive on both at 18 months resulted in 50.0% sensitivity and 95.8% specificity.  The ITC at 18 months, the M-CHAT at 24 months, and screening positive on both the M-CHAT and ITC at 18 months had the highest positive likelihood ratios of 7.8, 8.5, and 11.9 respectively, meaning that children with ASD are that much more likely to screen positive than those without ASD. The combination of screening positive on the M-CHAT at 18 or 24 months and the combination of screening positive on both the M-CHAT and ITC at 18 months had both sensitivity and specificity >70%.

Conclusions:  High-risk siblings are at elevated risk of ASD and also elevated risk of other developmental disorders. Therefore, it is important to examine the performance of tools that have been validated in low-risk samples to determine their utility in identifying siblings at the greatest risk of ASD. Performance on both tools was better in older children than in younger children, consistent with the literature (e.g., Pandey et al., 2008). Both the ITC and the M-CHAT demonstrated moderate sensitivity and moderate to good specificity at various ages; there was not a single tool at a specific age that was notably best at detecting ASD. However, the combination of M-CHAT at either age and the combination of either tool at 18 months met thresholds for adequate sensitivity and specificity; this suggests that in the complex developmental trajectories of siblings at risk for ASD, it will be important to consider multiple tools or multiple ages to best assess risk for ASD.