Examining the Diagnostic Validity of Autism Measures Among Adults in an Outpatient Clinic Sample.

BACKGROUND

Previous research has questioned the validity of diagnostic measures for autism spectrum disorder (ASD) among adults. This study examined the correspondence between several measures and clinician diagnosis.

METHODS

We conducted a retrospective chart review for 93 adults (18-61 years; 72% male) who received an ASD evaluation at a specialty outpatient clinic. Thirty-one individuals (33%) in the sample were diagnosed with ASD. We compared participant scores on the Autism Spectrum Quotient (AQ), the Ritvo Autism Asperger's Diagnostic Scale-Revised (RAADS-R), and the Autism Diagnostic Observation Schedule (ADOS) to clinician diagnosis of ASD. We calculated sensitivity, specificity, and area under the curve (AUC) for each measure.

RESULTS

Participants diagnosed with ASD scored significantly higher, on average, on the ADOS than those who were not diagnosed with ASD, but not on the RAADS-R or AQ. The AUC was relatively low for each measure: ADOS = 0.69 (95% confidence interval [CI] 0.58-0.81), RAADS-R = 0.58 (95% CI 0.46-0.72), and AQ = 0.40 (95% CI 0.28-0.52). Sensitivity and specificity of all three measures were in the poor to fair range. When dichotomized at the optimal cutoffs for this sample, the ADOS had a sensitivity of 0.65 and a specificity of 0.76; the RAADS-R had a sensitivity of 0.52 and a specificity of 0.73; and the AQ had a sensitivity of 0.45 and a specificity of 0.52.

CONCLUSIONS

Results of the study suggest that clinicians should not rely solely on self-report measures or the ADOS when diagnosing adults on the spectrum. Further development of measures is needed, including self-report measures with higher diagnostic validity, that are sensitive across age, gender, and cognitive functioning, and that differentiate autism from psychiatric diagnoses.

LAY SUMMARY

Diagnosing adults with autism spectrum disorder (ASD) is difficult. Other research has suggested that the few measures that exist for autistic adults may not be very effective for accurate diagnoses. We wanted to see how closely the results of commonly used ASD assessment tools compared with clinical diagnoses in a real-life outpatient setting. This study looked at adults who went to an adult ASD outpatient clinic for an initial ASD diagnosis over 3 years. Of these 93 adults, one-third were diagnosed as autistic. As part of the evaluation, all participants completed two commonly used autism screening surveys-the Autism Spectrum Quotient (AQ) and the Ritvo Autism Asperger's Diagnostic Scale-Revised (RAADS-R)-and took part in a semistructured diagnostic interview called the Autism Diagnostic Observation Schedule (ADOS). The clinicians also collected additional information and, when possible, spoke to family members before jointly making a diagnosis. The researchers compared how those diagnosed with ASD and those who were not diagnosed with ASD scored on the AQ, the RAADS-R, and the ADOS. Although adults on the spectrum scored higher on average on the ADOS clinical interview than those who did not receive an autism diagnosis, they did not score higher on the AQ and RAADS-R self-report measures. All three of the measures were only moderately effective at showing who would be diagnosed with ASD and who was not. These results confirm and expand on findings from other prior studies. The findings suggest that ASD diagnostic measures should not be used alone or considered the only source of information when making an initial autism diagnosis in adulthood. When studying the accuracy of diagnostic tests, it is best to compare the results of the tests being studied with an "independent gold standard," that is, a test that we know is very good and that is totally separate from the tests being studied. In this case, there is no clear "gold standard," so we had to compare the tests with the next best thing-the clinicians' final decision about whether or not a client has a diagnosis of ASD. It is possible that the clinicians did not make the right diagnosis. Also, the diagnosis was not "independent" of the tests being studied, since the clinicians used the results of the tests to help make the diagnosis. Clinicians only diagnosed about one-third of adults in this study with ASD, whereas previous studies in community clinics have had a higher percentage of adults diagnosed; this factor may have influenced the measures' accuracy. Lastly, clinicians in this study did not assess clients for any other mental health conditions, which may have provided more information about the clients who were not diagnosed with ASD. The findings from this study suggest that none of these measures are very accurate on their own. Thus, we recommend multiple measures (interviews and questionnaires) should be used together when clinicians diagnose ASD in adulthood. Results of this study also suggest that measures for adults with ASD should be tested in real-world community clinics, so that clinicians and researchers see how the measures perform when used for initial diagnosis in adulthood.