Results of Two Screening Tools Impact Diagnostic Outcome

Background:  In order for early autism intervention to help improve prognosis, early detection is crucial.  A variety of screening tools exist; however, no screening tool can identify all children with ASD. In this study, the Modified Checklist for Autism in Toddlers (M-CHAT(-R)) was administered to parents of toddlers, and the Screening Tool for Autism in Two-Year-Olds (STAT) was administered to a subset of screen negative and screen positive cases.

Objectives:  Examine whether diagnostic outcomes differ based on which measures children screened positive; in other words, does ASD-risk conveyed by M-CHAT(-R) and/or STAT relate to outcome? 

Methods:  Parents consented and completed the M-CHAT(-R) at their child’s 18- and/or 24-month pediatric check-up; screen positive cases were contacted by researchers to complete the M-CHAT(-R) Follow-Up; those who continued to screen positive were offered a free diagnostic evaluation, including the STAT.  Additionally, a subset of those who did not show risk on the M-CHAT(-R) completed the STAT, as well as a subsequent free evaluation if they demonstrated ASD risk on the STAT. The current sample (n=75; mean age at evaluation = 27.6 months, SD = 2.8) includes three sex- and age-matched groups: screen positive on both M-CHAT(-R) and STAT (BOTHpos), screen positive on M-CHAT(-R) and screen negative on STAT (M-CHATpos), and screen negative on M-CHAT(-R) and screen positive on STAT (STATpos). ASD diagnosis was based on ADOS(-2), structured parent interview, and clinical judgment. 

Results:  The sample was 64% male; race was 52% Black and 40% White. Chi-Square indicated that group (based on screening results) was related to diagnostic outcome, χ²(2, 75)=8.50, p=.014, Cramer’s V = .337. Specifically, adjusted residuals (all > ± 1.96) indicated that the STATpos group was less likely to have ASD (PPV = .32), and the BOTHpos group was more likely to have ASD (PPV = .72).  Additionally, ADOS comparison scores were examined across screening groups as a more dimensional approach to understanding ASD symptomatology. Results revealed that screening group was significantly related to ADOS comparison score, H(2) = 13.63, p = .001. Post-hoc Mann-Whitney U tests with Bonferroni corrections indicated higher ADOS severity score in the BOTHpos group compared to the STATpos group, U = 123.0, p < .001. The M-CHATpos group was not significantly different from the other two groups on diagnostic classification or ADOS outcome. When groups were restricted only to cases diagnosed with ASD, the ADOS severity score did not significantly differ, U = 2.50, p = .286.

Conclusions:  The BOTHpos group was more likely to be diagnosed with ASD and have higher ADOS severity than the STATpos group.   However, across groups children with ASD did not differ in severity of symptoms. The current study used the STAT as both a level two screening measure for use among at-risk samples as it was originally intended, and as a tool to identify missed ASD cases.  The results suggest that the highest likelihood of an ASD diagnosis is when a child screens positive on both screeners.