Validation of Olfactory Questionnaire in Koreans: an Alternative for Conventional Psychophysical Olfactory Tests

Background: The patients with coronavirus disease 2019 (COVID-19), a worldwide pandemic infection, frequently complain of olfactory disorders. However, psychophysical olfactory tests performed by an examiner are very difficult in these highly infectious patients. This study aimed to develop and validate a questionnaire for olfactory function that can be readily used to evaluate olfactory loss. Methods: Fourteen smell-related questions were created based on smells familiar to Koreans. Among them, questions with a kappa value of 0.6 or higher were finally selected through a test-retest reliability analysis. The correlations between the scores of the olfactory questionnaire and those of olfactory function tests (Butanol Threshold Test [BTT] and Cross Cultural Smell Identification Test [CCSIT]) were analyzed. To evaluate the predictive ability of the questionnaire and elicit cutoff values, receiver operating characteristic (ROC) curves were generated. Results: Out of the 14 questions in the questionnaire, 11 (kappa > 0.6) were selected for the olfactory questionnaire. We analyzed 2,273 subjects, and there was a significant correlation between the total score of the olfactory questionnaire and the BTT (r = 0.643, P< 0.001) or CCSIT (r = 0.615, P< 0.001) scores. ROC curves for the olfactory questionnaire, BTT, and CCSIT all demonstrated high predictive power to discriminate anosmia and severe hyposmia from normosmia. Regarding mild to moderate hyposmia, however, ROC curve for the olfactory questionnaire alone showed high predictive power of discrimination from normosmia. Based on the results of ROC curves among the subclasses, we suggest the classification of the total score of the questionnaire as 0-4, 5-17, 18-27, 28-41, and 42-44, for anosmia, severe hyposmia, moderate hyposmia, mild hyposmia, and normosmia, respectively. Conclusion: The total scores of the questionnaires correlated with the BTT and CCSIT scores. The symptom questionnaire for olfactory dysfunction may be useful as an alternative tool for olfactory function testing, when unavailable.

Automated summary

The study developed and validated a reliable olfactory function questionnaire for assessing olfactory loss in COVID-19 patients. The questionnaire showed significant correlations with conventional olfactory function tests and demonstrated high predictive power in discriminating different levels of olfactory dysfunction. This questionnaire could serve as an alternative tool for olfactory function testing in cases where traditional psychophysical tests are challenging to perform.