Evaluating Methods for Olfactory Assessment: A Comparative Longitudinal Analysis of Sniffin’ Sticks and Alternative Tools

Anosmia and hyposmia, referring to total or partial smell loss, respectively, affect 3-20% of people. The Sniffin' Sticks Extended Test, assessing odor threshold, discrimination, and identification (TDI), is a well-validated tool widely used in European and U.S. clinics. However, its time and resource demands limit routine use. During the COVID-19 pandemic, several rapid smell tests were developed, yet their classification performance and agreement with established psychophysical measures remain underexplored. We compared four alternatives-the Visual Analogue Scale for self-rated smell ability (VAS), the smell section of the Appetite, Hunger, and Sensory Perception questionnaire (AHSP), the Global Consortium for Chemosensory Research Smell Check (GCCR-Check), and the SCENTinel rapid smell test-against TDI scores in a longitudinal cohort of 96 adults (77 female patients; age 46.6 ± 10.5 years) with post-COVID-19 smell dysfunction, assessed up to five times over 12 months. Analyses used Generalized Estimating Equations for repeated measures, Bland-Altman plots for agreement and bias, and Receiver Operating Characteristic (AUC) curves for classification. No tool dominated across all TDI-defined categories. SCENTinel showed robust performance for anosmia (0.81) with the most balanced sensitivity-specificity trade-off among rapid tests, while GCCR-Check achieved the highest AUC for anosmia (0.88) and VAS best identified normosmia (0.73). Agreement analyses revealed systematic biases in self-report and rapid psychophysical tests. Rapid tools reliably detect anosmia, while classification performance decreases near diagnostic boundaries, particularly for normosmia. Combining brief self-report and short psychophysical measures may improve accuracy while maintaining feasibility for clinical and large-scale screening.