Diagnostic accuracy of the screenings Sniffin’ Sticks Test (SST-12) in COVID-19 induced olfactory disorders

by Emma J. A. Schepens, Inge Stegeman, Digna M. A. Kamalski

Objective olfactory function can be assessed using validated olfactory tests like the Sniffin’ Sticks Test (SST). However, their extensive nature makes them less suitable for clinical practice. To address this, shorter olfactory tests like the screenings Sniffin’ Sticks Test (SST-12) can be used for screening purposes and reduce testing time. The SST-12 serves as a diagnostic tool for screening olfaction in cases unrelated to COVID-19. However, these screening tests are uncertain regarding their accuracy in detecting olfactory dysfunction in patients with COVID-19 as the plausible cause. We aim to determine the diagnostic accuracy of the SST-12 in adults with post-COVID-19 olfactory dysfunction. We performed a diagnostic accuracy study with data from 113 consecutive COVID-19 diagnosed patients who experienced objectified smell loss ever since. At approximately 6 months after their diagnosis, all participants underwent the SST (reference standard), part of the SST was the SST-12 (index test). Diagnostic accuracy of the SST-12 is measured as negative predictive value (NPV), positive predictive value (PPV), sensitivity, and specificity. The SST-12 detected smell loss in 85 patients among 91 patients with smell loss and ruled out smell loss in 15 patients among the 22 patients without smell loss based on the reference standard. Making sensitivity 93.4% (CI 0.87–0.97), and specificity 68.2% (CI 0.48–0.85). Out of the 92 patients with a positive test result on SST-12, 85 patients had indeed smell loss (PPV 92.4% CI 0.86–0.97), and out of the 21 patients with a negative test result, 15 patients had no smell loss regarding the reference standard (NPV 71.4% CI 0.50–0.88). The findings suggest that the SST-12 holds promise as a useful tool for identifying individuals with smell loss, also in individuals with COVID-19 as cause, but it is important to have a good understanding of the interpretation of the results of the SST-12 when considering its implementation in clinical practice.