What Modified Checklist for Autism in Todler (mCHAT) score is concerning?

Concerning M-CHAT Scores for Autism Screening

An M-CHAT score of 3 or higher initially, and 2 or higher after follow-up interview, is concerning and warrants referral for diagnostic evaluation, as this indicates a 47.5% risk of autism spectrum disorder (ASD) and a 94.6% risk of any developmental delay. 1

Understanding M-CHAT Scoring and Risk Levels

The Modified Checklist for Autism in Toddlers (M-CHAT) is a validated screening tool used primarily for toddlers between 16-30 months of age. Based on the most recent evidence, the M-CHAT-R/F (Revised with Follow-up) uses a three-tier risk stratification system:

Risk Categories:

• Low Risk (0-2 points): Continue routine developmental surveillance
• Medium Risk (3-7 points): Administer follow-up interview; refer for diagnostic evaluation if score remains ≥2 after follow-up
• High Risk (8-20 points): Bypass follow-up interview and refer immediately for diagnostic evaluation 1

Clinical Significance of M-CHAT Scores

The positive predictive value (PPV) of the M-CHAT varies significantly based on:

1. Age of screening:

   • PPV is lower in younger children (16-23 months): 0.28
   • PPV is higher in older children (24-30 months): 0.61 2

2. Risk status:

   • Low-risk population: PPV = 0.11 without follow-up; improves to 0.65 with follow-up interview
   • High-risk population: PPV = 0.60 without follow-up; improves to 0.76 with follow-up interview 2

3. Follow-up interview impact:

   • The follow-up interview is essential as it significantly improves PPV and reduces false positives
   • In the largest sample to date (N=18,989), PPV for ASD with follow-up was 0.54, and for any developmental disorder was 0.98 2

Implementation Recommendations

Optimal Screening Protocol:

1. Initial screening: Administer M-CHAT-R at 18 and 24-month well-child visits
2. Risk stratification:
   • Score 0-2: Low risk, continue routine monitoring
   • Score 3-7: Medium risk, conduct follow-up interview
   • Score ≥8: High risk, refer directly for evaluation 1
3. After follow-up interview:
   • If score remains ≥2: Refer for diagnostic evaluation
   • If score <2: Low risk, continue routine monitoring

Important Clinical Considerations:

• Children with initial scores of 3-7 (93% of all cases) require the follow-up interview
• Children with scores ≥8 (1% of all cases) should be referred directly for diagnostic assessment 2
• The follow-up interview is critical as it reduces false positives while maintaining sensitivity

Pitfalls and Caveats

• Age considerations: M-CHAT may be less accurate at 18 months compared to 24 months 3
• False negatives: Some children with ASD may be missed by M-CHAT screening, particularly those with more subtle presentations
• Cultural factors: Validation studies in different populations show varying PPVs (e.g., 0.19 in a Spanish sample) 2
• Developmental context: A positive M-CHAT may detect not only ASD but also other developmental delays, speech delays, and social anxiety 4
• Follow-up completion: In implementation studies, only about 60-63% of screen-positive children completed diagnostic evaluations 2

Benefits of Early Detection

Early identification through M-CHAT screening can lower the age of ASD diagnosis by approximately 2 years compared to national averages, significantly increasing the time available for early intervention 1. In one implementation study, children were diagnosed at a mean age of 24 months following M-CHAT screening 4, which is substantially earlier than typical diagnosis ages.

Remember that while M-CHAT is a valuable screening tool, it is not diagnostic, and all children with concerning scores should be referred for comprehensive evaluation by specialists in ASD diagnosis.