Development and validation of the four-item Concise Aging adults Smell Test to screen for olfactory dysfunction in older adults

Background: Olfactory dysfunction (OD) in the elderly is common and associated with numerous comorbidities, yet often underrecognized. This study sought to develop an instrument for widespread screening of this condition. Methods: Demographic factors, comorbidities, and olfactory-related questions were examined in a focus group (N = 20) and development cohort (N = 190). The 4-item Concise Aging adults Smell Test (4-CAST) screening instrument was then developed to predict OD on Sniffin Sticks testing. An independent validation cohort (N = 147) was then examined to confirm ability of the 4-CAST to predict OD on Smell Identification Test 40 (SIT40). Results: The most important variables for predicting olfactory loss in older subjects were age, type II diabetes status, Visual Analog Scale (VAS) of overall rating of smell, and VAS of impact of smell upon safety. In the development cohort, the 4-CAST model yielded predictive probability (area under the curve) of 0.805 (p < 0.001) for predicting the bottom 25th percentile on Sniffin Sticks. Results were similar in the validation cohort, as the 4-CAST accurately classified 83.8% subjects (area under the curve [AUC] 0.789, p < 0.001) in the bottom 25th percentile of SIT40 testing. The 4-CAST was able to accurately classify 89.4% of subjects with anosmia. Conclusion: The 4-CAST is a quick screening instrument for predicting OD in older adults and has similar performance characteristics in independent populations using the two most common validated olfactory tests. Given the high prevalence of unrecognized olfactory loss in this population, this can be a useful tool for practitioners to determine which subjects may benefit from more extensive olfactory testing.