Should I administer the Modified Checklist for Autism in Toddlers (M-CHAT) to a 36-month-old child who has never undergone the screening?

M-CHAT Screening for a 36-Month-Old Child

Yes, you should administer the M-CHAT screening to a 36-month-old child who has never had it done, as this represents a missed opportunity for early detection of autism spectrum disorder (ASD) that could still benefit the child. 1

Evidence-Based Rationale

The Modified Checklist for Autism in Toddlers (M-CHAT) and its revised versions (M-CHAT-R/F) are designed primarily for screening children between 18-30 months of age. However, for a 36-month-old who has missed previous screening opportunities, conducting the screening now is still valuable for several reasons:

Benefits of Late Screening

• While the optimal screening age is 18-24 months, evidence supports that ASD screening at or after 24 months may have better specificity than earlier screening 1
• The M-CHAT has been validated for children up to 36 months of age 2
• Early detection, even at 36 months, is still significantly earlier than the national median age of diagnosis (around 4-5 years), allowing for earlier intervention 2

Screening Process for a 36-Month-Old

1. Administer the M-CHAT-R/F questionnaire to the parents
2. If the initial score is ≥3, proceed with the follow-up interview
3. If the score remains ≥2 after follow-up, refer for comprehensive diagnostic evaluation 2

Clinical Implications

The M-CHAT-R/F has demonstrated strong clinical utility:

• Children scoring ≥3 initially and ≥2 after follow-up have a 47.5% risk of ASD diagnosis and a 94.6% risk of any developmental delay or concern 2
• The follow-up interview component is crucial for reducing false positives 3

Important Considerations

Potential Limitations

• The M-CHAT was primarily validated for the 18-30 month age range, so sensitivity may be different at 36 months
• Some behaviors typical of ASD may be more established and evident at 36 months, potentially improving detection

Risk Assessment

While the USPSTF notes insufficient evidence for universal screening recommendations 1, this applies to asymptomatic children. For a child who has missed recommended screening windows, conducting the screening represents appropriate catch-up care.

Action Steps

1. Administer the 23-item M-CHAT-R questionnaire to the parents
2. Score the questionnaire immediately
3. If score is ≥3, conduct the follow-up interview during the same visit if possible
4. If the child screens positive after follow-up (score ≥2), refer promptly for comprehensive developmental evaluation
5. Even if the screen is negative, maintain vigilance for developmental concerns at subsequent visits

Remember that the M-CHAT-R/F is a screening tool, not a diagnostic instrument. A positive screen indicates the need for further evaluation, not an ASD diagnosis.