Determination of retronasal odor threshold values

Objective and Hypothesis The present study aimed to generate the normative data of the retronasal odor threshold values for normosmic and hyposmic subjects and to test the validity by determining the normosmic/hyposmic discrimination of the retronasal odor threshold test. Materials and Methods Twenty normosmic and 20 hyposmic cases, who were evaluated by Sniffin' Sticks odor test in Dokuz Eylul University, Otorhinolaryngology Department Rhinology Laboratory between April 2017 and October 2017, were included in the study. Before the Sniffin' Sticks test, the detailed otorhinolaryngologic examinations of the cases were performed and the cases with pathological findings affecting the sense of odor negatively were excluded from the study. The Sniffin' Sticks odor thresholds, odor discrimination, odor identification and TDI scores were recorded. For the retronasal odor threshold test, 13 sets of test batteries consisting of concentrated solutions which were formerly prepared from 99% phenylethyl alcohol (PEA) with 2: 1 dilution (PEA) in the Rhinology Laboratory of our clinic and water were used. In each row, each concentration underwent with the water control and when a correct response was not given, the same procedure was continued by going up to a higher row. The value in which four consecutive correct responses were given was identified as the patient's retronasal odor threshold value. Results According to the analysis results, age was found to affect the retronasal odor threshold value (p<0.001) whereas gender, cigarette and alcohol were found to not to affect the retronasal threshold value (p>0.05). When the Sniffin' Sticks test threshold, discrimination, identification and TDI scores, retronasal threshold values of the normosmic and hyposmic cases were compared, the scores of the normosmic group was statistically significantly higher than that of the hyposmic group (p<0.001). A strong correlation was detected between the Sniffin' Sticks TDI scores and retronasal odor threshold values in the normosmic group (p<0.001, r:0,67) while a very strong correlation was detected the Sniffin' Sticks TDI scores and retronasal odor threshold values in the hyposmic group (p<0.001, r:0,81). At the same time, as a result of ROC analysis, the normosmic and hyposmic discrimination of retronasal odor threshold test was found to have 95% sensitivity and 100 % specificity. The cut off value was determined as 8.5. Conclusion It was shown in this study that a retronasal odor test which is a psychophysical odor test, can be performed using oral stimuli and it is possible to discriminate between normosmic and hyposmic subjects. Retronasal odor thresholds are an additional method for assessing the olfactory function. In future studies, it is useful to study the threshold values of retronasal odor in different conditions and diseases.