At what ages is the Modified Checklist for Autism in Toddlers, Revised (M‑CHAT‑R) administered?

M-CHAT-R Administration Age

The M-CHAT-R is administered to children aged 16 to 30 months, with optimal screening recommended at 18 and 24 months. 1

Recommended Screening Ages

The evidence from pediatric guidelines clearly establishes the validated age range:

• Primary screening window: 16-30 months 1, 2
• Optimal timing: 18 and 24 months 1
• Can be used up to 48 months, though validated primarily for the younger age range 3, 4

Age-Related Performance Considerations

The screening accuracy of the M-CHAT-R varies significantly by age, which is critical for clinical interpretation:

Younger children (16-23 months):

• Lower positive predictive value (PPV = 0.28) 1
• Higher false-positive rates due to developmental variability 1
• Still valuable for detecting ANY developmental disorder (PPV = 0.98 for any developmental concern) 1

Older children (24-30 months):

• Substantially better positive predictive value (PPV = 0.61) 1
• More reliable ASD-specific detection 1
• Reduced false-positive burden 1

Clinical Implementation Strategy

For routine well-child visits:

1. Screen at the 18-month visit as recommended by AAP guidelines 1
2. Repeat screening at 24 months 1
3. Always use the follow-up interview for screen-positive cases (improves PPV from 0.058 to 0.65) 1

Important caveats:

• Screening before 18 months has lower sensitivity and higher false-negative rates 1
• Performance degrades outside the 16-30 month optimal window 5
• Children screening positive at 18 months should receive diagnostic evaluation even with lower PPV, as they often have identifiable developmental concerns requiring intervention 1

The evidence consistently demonstrates that repeated screening (at both 18 and 24 months) improves sensitivity with minimal cost to specificity 6, making this the preferred approach when feasible in clinical practice.