“True Misses” : The Characteristics of Missed Screening Cases

Background:

The American Academy of Pediatrics recommends autism specific screening at 18 and 24 months of age. Several ASD screening tools have been developed, though few have been evaluated longitudinally to ascertain a more accurate estimate of sensitivity and specificity. Studying potential “missed” cases provides an opportunity to obtain a more accurate understanding of both the sensitivity of the screener as well as the characteristics of children who are missed by the instrument. 

Objectives:

This study provides preliminary data from a 2-year follow-up screening with the Modified Checklist for Autism in Toddlers (M-CHAT). The focus of the follow up is to assess the characteristics of potential “missed” screening cases, or children who screen negative on the ASD screening instrument but are later found to have an ASD diagnosis.  

Methods:

Participants were drawn from a sample of children who passed the M-CHAT when screened between 16 and 30 months of age. Approximately 2 years later children were rescreened; the M-CHAT was mailed to families with a stamped envelope to return the form to the study. Rescreeners were sent back for 2996 children. A portion of the children rescreened with the M-CHAT were also screened with the Social Communication Questionnaire (SCQ) (n=1407) which was added to the study later. 

Results:

At follow-up, 42 of the 2996 children were identified as “potential misses” and seen for diagnostic evaluation.  28 children were identified based on screening results (screening positive on the M-CHAT or SCQ), 11 children had a caregiver report that he/she received an ASD evaluation referral or diagnosis since their initial screening, and 3 were flagged by a healthcare provider. Fifteen children were diagnosed with ASD and classified as “true misses.”

The majority (92.3%) of the true misses were male. The average age at initial screening was 22.8 months (SD=5.96); there was no difference in regards to whether the initial screening occurred at 18 or 24 months of age (46.2% were screened at 18-months and 53.8% were screened at 24-months). The mean M-CHAT score of the true misses at initial screening was 1.58 failed items of a possible 23 (SD=1.084); the mean M-CHAT score at follow up was significantly higher at 5.33 (SD=4.271) (t=-3.174, p<.01).

The average age at follow up evaluation was 52.2 months (SD=6.29). All true misses received ASD diagnoses at follow up: 10 with Autistic Disorder, 3 with PDD-NOS, and 2 with Asperger’s Disorder.

Conclusions:

This study was designed to present preliminary data on a sample of missed screening cases. The results suggest that missed cases are largely identified by follow-up screening. The missed cases in this sample were more likely to be male and presented with significantly higher (more impaired) scores on the screening instrument at follow-up. This could be because there was regression after the initial screening, in which skills initially reported were lost, or because parents reported more accurately at age 4 than at age 2.