Estimating the cut-off point of Xerostomia Inventory questionnaire score to diagnose dry mouth based on non-stimulating saliva test: a diagnostic sensitivity and specificity study.

Aim: Xerostomia is defined as a subjective complaint of dry mouth and is a prevalent condition. The study aims to estimate the cut point of the xerostomia inventory (XI) questionnaire for diagnosing dry mouth based on a saliva test.

Method: This prospective study was conducted in Dentistry School of Kerman University of Medical Sciences. Eligibility criteria included individuals aged 40 and above who were capable of undergoing saliva testing. For each randomly selected participants, a non-stimulating saliva test as a reference test was taken between 9:00 AM and 12:00 PM. Participants were asked to avoid eating, drinking and smoking 60 min before and during the test. For 5 min, the patient poured the accumulated saliva in his mouth every 1 min by bending forward into the container. If the collected saliva was less than 0.1 ml during 1 min, the participant was diagnosed with dry mouth. The Persian version of the XI questionnaire as an index test was used to calculate the xerostomia score, which was determined by summing the scores for each question. The diagnostic power of the questionnaire was assessed using receiver operating characteristic curve, and Youden index was utilized to identify the positivity cut off point.

Results: In this research, 120 people who referred to the Faculty of Dentistry in 2022-2023 who were participated. Of all participants, 50% in the study were women. The average age of the participants in the study was 50.2 ± 7.2 years. Among the participants, 40 experienced dry mouth. The positivity cut-off point for the diagnosis of dry mouth was xerostomia score greater than 23.5, which has a sensitivity of 82.5% and a specificity of 81.5%. The area under curve for the questionnaire was 0.898.

Conclusions: The XI questionnaire cut point of 23.5 demonstrated high sensitivity and specificity for diagnosing dry mouth in individuals over 40 years old. Results for specific age or gender subgroups should be interpreted with caution.