ASD Screening at 18 and 24 Months: Incremental Validity and Characteristics of Screen Positive Cases

Background: The American Academy of Pediatrics has recommended autism screening for all children at 18 and 24 months, but empirical data are lacking to determine the added value of screening at two time points.

Objectives:  To investigate the incremental validity of a second screen at 24 months and compare children  who screened positive on a second autism screening at 24 months to children who screened positive at 24 months without a previous autism screen.

Methods: The 2-stage M-CHAT with Follow-Up (M-CHAT/F) was used to screen children at 18 and 24 month pediatric well child visits; screen positive cases were evaluated and classified with an Autism Spectrum Disorder (ASD) or non-ASD. Participants in the current study include children who screened positive at 24-months.

Results:  Of 7,364 children screened with M-CHAT at both 18 and 24 months, 32 children screened negative on the M-CHAT(/F) at 18 months and screened positive on the M-CHAT/F at 24 months. The sample was majority male (59.4%) and represented a range of races/ethnicities (34.4% White, 34.4% African American, 12.5% Hispanic/Latino). Of the 32 cases, 9 families declined the diagnostic evaluation. Of the 23 children who received evaluations, 11 children were diagnosed with an ASD (5 Autistic Disorder, 6 PDD-NOS), 9 children received other DSM-IV or ICD-10 diagnoses, 2 children were classified as “at risk” with developmental concerns, and one child was typically developing.

All children who screened positive with a second autism screening at 24 months (n=23) were compared to children who screened positive at 24 months without a previous autism screen (n=145). There were no differences between the samples in regards to autism symptoms or severity as measured by the ADOS total score (t=-.636, p=.526) or the CARS total score (t=-.901, p=.369). When comparing cognitive functioning as measured by the Mullen Scales of Early Learning (MSEL), there were no differences between the two groups in receptive or expressive language skills. There was a trend towards significance on the MSEL Fine Motor domain (t=1.921, p=.056) and a significant difference on the MSEL Visual Reception domain (t=2.096, p=.038). The children who were identified with a second autism screening at 24 months had higher t-scores on both the Fine Motor (32.4 vs. 27.9) and Visual Reception (36.9 vs. 31.1) domains.  

Conclusions: Completing a second autism screening at 24 months identified 11 additional cases of ASD. There were no significant differences between children who screened positive on a second autism screening as compared to children who screened positive without a previous autism screen, with the exception of performance on the MSEL Visual Reception domain.  Additional investigation is needed to identify potential differences between the samples, which might help identify children who are likely to be “missed” by an autism screen at 18 months.