Expediting clinician assessment in the diagnosis of autism spectrum disorder

Abstract

Aim: To investigate a novel observational rating protocol designed to expedite clinical diagnosis of autism spectrum disorder (ASD).

Method: Two hundred and forty patients referred to a tertiary autism center (median age 8y 9mo, range 2y 6mo-34y 8mo; 188 males, 52 females) were rated using an adaptation of the Childhood Autism Rating Scale, Second Edition (CARS-2) based exclusively on patient observation (CARS-2^obs ). Scores were compared to expert diagnosis of ASD, parent-reported Social Responsiveness Scale, Second Edition (SRS-2) and, in a selected subset of patients, the Autism Diagnostic Observation Schedule, Second Edition (ADOS-2).

Results: CARS-2^obs distinguished patients with a clinical diagnosis of ASD from those with non-ASD neuropsychiatric disorders (mean score=18 vs 11.7, p<0.001). Severity ratings on the CARS-2^obs correlated with the ADOS-2 (r=0.68, ρ=0.64) and SRS-2 (r=0.31, ρ=0.32). A CARS-2^obs cutoff point equal to or greater than 16 demonstrated 95.8% specificity and 62.3% sensitivity in discriminating individuals with ASD from individuals without ASD in a specialty referral setting.

Interpretation: The CARS-2^obs allows the rapid acquisition of quantitative ratings of autistic severity by direct observation. Coupled with parent/teacher-reported symptoms and developmental history, the measure may contribute to a low-cost diagnostic paradigm in clinical and public health settings, where positive results might help reduce delays in diagnosis, and negative results could prompt further specialty assessment.

What this paper adds: The Childhood Autism Rating Scale, Second Edition based on patient observation distinguished individuals with versus without autism spectrum disorder (ASD). A score equal to or greater than 16 on this assessment showed high specificity for a diagnosis of ASD.

Figure 1

(a) Scaled Social Responsiveness Scale, Second Edition (SRS‐2) total score distribution comparison between patients diagnosed with autism spectrum disorder (ASD) and patients without such a diagnosis (ASD ruled out). (b) Childhood Autism Rating Scale, Second Edition based on patient observation (CARS‐2^obs) score distribution comparison between patients with ASD and patients without (ASD ruled out). All patients had been referred to the Autism Clinical Center for suspicion of ASD and were ultimately diagnosed with ASD or another primary diagnosis.

Figure 2

(a) Regression plot of the Childhood Autism Rating Scale, Second Edition based on patient observation (CARS‐2^obs) and Autism Diagnostic Observation Schedule, Second Edition (ADOS‐2) for all patients. (b) Regression plot of the CARS‐2^obs and raw Social Responsiveness Scale, Second Edition (SRS‐2) total scores for all patients. The line of best fit is noted along with the 95% confidence intervals and 95% prediction limits. Although there is evidence of overestimation for a CARS‐2^obs greater than 25, suggesting that the relationship may not be uniformly linear, removal of this group of individuals did not significantly affect the model.

Figure 3

Receiver operating characteristic curve calculated for the total Childhood Autism Rating Scale, Second Edition based on patient observation (CARS‐2^obs) score. Individual tested cutoff points with corresponding scores are noted on the graph.