Glottal function index as a brief screening tool: Determination of an optimal cutoff score for functional dysphonia

This study aimed to evaluate the diagnostic utility of the Glottal Function Index (GFI) in distinguishing individuals with functional dysphonia from normophonic controls and to determine an optimal cutoff score for screening. A total of 100 participants (50 males, 50 females) were included in this case–control study. The study group (SG) comprised 50 patients with functional dysphonia, and the control group (CG) included 50 age- and gender-matched healthy individuals. All participants underwent a multidimensional voice assessment, including acoustic analysis, auditory-perceptual evaluation (GRBAS), aerodynamic measurement [Maximum Phonation Time (MPT)], and self-reported outcome measures [Voice Handicap Index-10 (VHI-10), Voice-Related Quality of Life (V-RQoL), and GFI]. Group comparisons were performed, and receiver operating characteristic (ROC) analysis was used to determine the optimal GFI cutoff based on the Youden index. ROC analysis demonstrated excellent diagnostic accuracy for the GFI in functional dysphonia (AUC = 0.983). The optimal cutoff score was ≥ 3, providing 96% sensitivity and 96% specificity. The SG exhibited significantly higher GFI scores [median 14 (9.75–19)] than the CG [0 (0–0)] (p < 0.001). The SG also showed significantly deteriorated acoustic (increased shimmer, decreased harmonics-to-noise ratio), auditory-perceptual (higher G score), aerodynamic (shorter MPT), and self-reported (higher VHI-10, lower V-RQoL) parameters than the CG (all p < 0.001). The GFI is a highly sensitive self-report tool for identifying functional dysphonia. A cutoff score of ≥ 3 provides excellent diagnostic accuracy and supports its use as a brief screening measure within multidimensional voice assessment protocols.