What you need to know

Between 20% and 67% of people who get COVID-19 develop some type of smell disorder, depending on the SARS-CoV-2 variant they are infected with. Tests have already been developed that measure loss of smell, whether total (anosmia) or partial (hyposmia). However, these tests are difficult to carry out on a widespread scale during a pandemic. To be applied at the population level, a rapid and readily available test that can discriminate between different kinds and degrees of smelling loss is needed.

In a study supported by the National Institute on Deafness and Other Communication Disorders (NIDCD), researchers developed a self-administered diagnostic test to measure both quantitative smelling loss (anosmia or hyposmia) and qualitative smelling loss, such as perceiving odors differently than usual (parosmia) or smelling odors that are not there (phantosmia).

What did the researchers do?

Early in the COVID-19 pandemic, researchers at the Monell Chemical Senses Center created a self-administered test to detect, identify, and measure the intensity of a flower odor. This test was called SCENTinel 1.0, and the researchers believed it could be useful in screening for COVID-19. Their current work builds on that success with the development of a more refined screening tool.

For this study, the researchers created SCENTinel 1.1, a new rapid test, and gave it to participants who reported having smell disorders. Most participants had been diagnosed with a loss of smell from COVID-19, but some participants with no loss of smell were included.

The participants reported on their current sense of smell — did they have partial or complete loss of smell, were they experiencing odors differently than usual, or were they smelling things that were not actually there? On the test card, they were asked to identify the odor they smelled — for example, a flower, coffee, bubblegum, or caramel popcorn — and its intensity. They also reported on the odor’s pleasantness.

The researchers examined how closely the results from the SCENTinel 1.1 test corresponded to the self-reports. Total or partial smell loss were classified as quantitative disorders, and distorted (parosmia) or phantom (phantosmia) smells were classified as qualitative disorders.

The researchers found that the SCENTinel 1.1 test was able to discriminate between quantitative and qualitative smelling disorders and rapidly tell when someone’s sense of smell was distorted.

Why is this research important?

Diagnosing smell disorders is complex. SCENTinel 1.1 hopes to provide a fast, inexpensive way to differentiate between different conditions affecting the sense of smell, including COVID-19, which may be useful in research and for better targeting treatments for these conditions.

Where can I go to learn more?

SCENTinel 1.1, Second Iteration of Monell’s Rapid Smell Test, Discriminates Between Smell Loss and Smell Distortion

• The Monell Chemical Senses Center describes its research findings.

Sniffing Out COVID-19

• NIH has supported multiple researchers in the development of smell tests related to COVID-19.

Smell Disorders

• NIDCD shares information on the diagnosis and treatment of smell disorders.

Sources

Hunter, S. R., Hannum, M. E., Pellegrino, R., O’Leary, M. A., Rawson, N. E., Reed, D. R., Dalton, P. H., & Parma, V. (2023). Proof-of-concept: SCENTinel 1.1 rapidly discriminates COVID-19-related olfactory disorders. Chemical Senses, 48, bjad002. https://doi.org/10.1093/chemse/bjad002

Parma, V., Hannum, M. E., O’Leary, M., Pellegrino, R., Rawson, N. E., Reed, D. R., & Dalton, P. H. (2021). SCENTinel 1.0: Development of a rapid test to screen for smell loss. Chemical Senses, 46, bjab012. https://doi.org/10.1093/chemse/bjab012