What is the recommended screening and intervention process for Autism Spectrum Disorder (ASD) using the M-CHAT-R (Modified Checklist for Autism in Toddlers - Revised) screening tool?

M-CHAT-R/F Screening Protocol for Autism Spectrum Disorder

Use the Modified Checklist for Autism in Toddlers, Revised with Follow-Up (M-CHAT-R/F) at both 18 and 24 months during well-child visits, with a two-stage screening process that includes a structured follow-up interview for positive screens before referral. 1, 2

Screening Timeline and Administration

Universal screening should occur at 18 and 24 months of age during routine well-child visits, as recommended by the American Academy of Pediatrics. 1 The M-CHAT-R/F is a parent-rated questionnaire that assesses communication skills, joint attention, repetitive movements, and pretend play. 3, 2

Special Population Considerations

• Siblings of children with ASD require intensified surveillance with mandatory screening at minimum at both 18 and 24 months due to their elevated risk of 14-18%. 1, 4

Two-Stage Scoring Algorithm

The M-CHAT-R/F uses a three-level risk stratification system that determines the next clinical action:

Stage 1: Initial Screening Score

• Low Risk (0-2 points): Screen negative; continue routine developmental surveillance 2
• Medium Risk (3-6 points): Administer structured follow-up interview 2
• High Risk (≥7 points): Skip follow-up interview and refer immediately for diagnostic evaluation and early intervention 2

Stage 2: Follow-Up Interview (for Medium Risk only)

• Score ≥2 after follow-up interview: Positive screen—refer for comprehensive diagnostic evaluation 2, 5
• Score <2 after follow-up interview: Negative screen—continue routine surveillance 2

Clinical Performance Characteristics

The screening accuracy varies significantly by age and risk population:

• At 18 months: PPV = 0.28 for younger toddlers (16-23 months), indicating higher false-positive rates 2, 6
• At 24 months: PPV = 0.61 for older toddlers (24-30 months), demonstrating improved accuracy 2
• With follow-up interview: PPV improves to 0.43-0.65 in low-risk samples and 0.76 in high-risk samples 2
• Overall diagnostic yield: 47.5% risk of ASD diagnosis and 94.6% risk of any developmental delay when scoring ≥3 initially and ≥2 after follow-up 5

Critical Implementation Points

The follow-up interview is essential and significantly improves specificity, reducing false positives while maintaining sensitivity. 4 Without the structured follow-up, the PPV drops to only 0.058 in low-risk samples. 3

What the Screening Assesses

The M-CHAT-R/F evaluates key early markers of ASD that emerge between 12-24 months:

• Reduced social attention and social communication 1
• Failure to respond to name at 12 months 1
• Fewer nonverbal behaviors to initiate shared experiences 1
• Deficits in joint attention initiation 1
• Less frequent eye contact 1
• Increased repetitive behavior with objects 1

Referral Pathway After Positive Screen

Immediately refer all children who remain screen-positive after the two-stage process for comprehensive diagnostic evaluation and appropriate early intervention services, without waiting for additional developmental milestones. 1 Children diagnosed through this screening process are diagnosed approximately 2 years younger than the national median age of diagnosis (mean age 23.1 months in screened populations versus national median of 4-5 years). 5, 7

Important Caveats and Limitations

• Screening at 18 months has lower specificity than 24 months, but the positive predictive value for any diagnosable developmental disorder remains high, making the screen clinically valuable even with higher false-positive rates for ASD specifically. 1
• False positives may occur due to developmental concerns that may resolve or behaviors in typically developing toddlers that overlap with ASD deficits. 2
• Screen-negative children still require ongoing developmental surveillance at all well-child visits, as some children with ASD will be missed (sensitivity is not 100%). 1, 7

Conflicting Evidence Note

The U.S. Preventive Services Task Force (USPSTF) issued an "I" statement (insufficient evidence) regarding universal ASD screening in asymptomatic children, noting lack of direct evidence on clinical outcomes from screening. 3 However, the American Academy of Pediatrics maintains its recommendation for universal screening at 18 and 24 months based on the established early markers of ASD, high diagnostic stability after 24 months, and benefits of early intervention. 1, 4 In clinical practice, follow the AAP recommendation for universal screening, as the potential benefits of early detection and intervention outweigh the minimal harms of screening and behavioral interventions. 1