M-CHAT Screening Tool Interpretation for Autism
Primary Scoring and Risk Stratification
The M-CHAT-R/F uses a two-stage screening process where an initial score of ≥3 triggers a follow-up interview, and a score of ≥2 after the follow-up interview indicates significant risk for ASD requiring immediate referral for diagnostic evaluation. 1
Three-Level Risk Algorithm
- Low Risk (0-2 points): No further action needed; continue routine developmental surveillance 1
- Medium Risk (3-6 points): Administer structured follow-up interview to clarify responses 1, 2
- High Risk (≥7 points): Skip follow-up interview and refer immediately for comprehensive diagnostic evaluation and early intervention 3, 1
Critical Items and Discriminatory Power
The six items with the best discriminability between children with and without ASD focus on social relatedness and communication 4:
- Response to name
- Joint attention behaviors
- Interest in other children
- Showing/bringing objects to share
- Imitation
- Response to pointing
Age-Specific Performance Characteristics
Optimal Screening Ages
- 18 and 24 months: American Academy of Pediatrics recommends universal ASD-specific screening at both timepoints 5
- Performance varies significantly by age: PPV for ASD is 0.28 in younger children (16-23 months) versus 0.61 in older children (24-30 months) in low-risk populations 1, 6
Sensitivity and Specificity
- With follow-up interview: Sensitivity ranges from 0.44 to 0.93 depending on population and cutoff used 3
- Specificity: Approximately 0.99 in general population screening 3
- PPV varies by risk level: 0.43-0.65 in low-risk samples with follow-up, 0.76 in high-risk samples with follow-up 1
Two-Stage Screening Process
Stage 1: Initial M-CHAT-R Questionnaire
- 23-item parent-completed yes/no questionnaire 4
- Assesses communication skills, joint attention, repetitive movements, and pretend play 1
- Takes approximately 5 minutes to complete
Stage 2: Follow-Up Interview (if Stage 1 positive)
- Critical importance: The follow-up interview dramatically improves specificity and reduces false positives 3, 2
- Without follow-up, PPV drops to 0.058; with follow-up, PPV improves to 0.11-0.65 depending on risk level 3
- 93% of children with initial scores of 3-6 did not require further evaluation after follow-up interview 3
Clinical Decision-Making Based on Results
After Follow-Up Interview
If ≥2 items remain positive after follow-up: Refer immediately for:
- Comprehensive diagnostic evaluation by developmental specialist 1, 2
- Early intervention services (do not wait for diagnosis) 5
- Audiological evaluation to rule out hearing loss 7
If <2 items positive after follow-up: Continue enhanced developmental surveillance at all well-child visits 5
Important Caveats and Pitfalls
False Positives
- Higher false-positive rates occur before 24 months, but children who screen positive still have 94.6% risk of any developmental delay or concern, making referral appropriate 2
- Overlapping behaviors between typically developing toddlers and early ASD can cause false positives 1
- Developmental concerns may resolve in some cases 1
Population-Specific Considerations
High-risk populations (siblings of children with ASD):
- 14-18% risk of ASD 7, 5
- Require intensified surveillance with screening at minimum at 18 and 24 months 7, 5
- Higher PPV (0.76-0.79) makes screening more predictive 1, 6
Low-risk populations:
- Lower PPV, especially in younger children 6
- Balance early identification against lower specificity 6
- Even with lower ASD-specific PPV, high detection rate for any developmental disorder justifies screening 2, 8
Diagnostic Stability
- Diagnosis at ≥24 months is well-established and stable 7
- Diagnosis before 24 months may have higher false-positive rates but still warrants intervention 3, 7
- Children diagnosed using M-CHAT-R/F were diagnosed 2 years younger than national median age 2
What NOT to Use
Original CHAT (not M-CHAT): Has unacceptably low sensitivity of 18% and is not recommended for current screening 3, 7