Olfactory testing is a medical evaluation that measures and quantifies a person’s sense of smell. People with a diminished sense of smell may not be aware of their deficit, and testing can clarify if a perceived loss of flavor is rooted in smell rather than taste. The evaluation provides a baseline for healthcare providers to understand the nature and severity of an olfactory disorder.
Reasons for Olfactory Testing
Olfactory testing may be recommended for several reasons, including:
- Smell loss following a viral illness. Respiratory viruses, including the one responsible for COVID-19, can lead to smell dysfunction. Testing helps gauge the impairment’s extent and monitor potential recovery.
- Early detection of neurodegenerative diseases. A decline in smell can be an early indicator of conditions like Parkinson’s or Alzheimer’s disease. Testing provides data that aids in the early identification of these disorders.
- Assessment of physical nasal issues. Chronic sinus disease, nasal polyps, or tumors can create blockages that prevent odors from reaching the olfactory epithelium. Head trauma can also damage olfactory nerves, and testing assesses the functional impact.
- Evaluation of environmental or occupational exposure. Exposure to certain chemicals and toxins can harm olfactory function. Testing provides a standardized method to document this loss for occupational health assessments.
Types of Olfactory Tests
The most common methods for evaluating the sense of smell are psychophysical tests, which measure a person’s reported perception of an odor. These tests are categorized as identification, threshold, or discrimination tests. The results help pinpoint if the issue is in the nose or the brain’s processing of smells.
Odor identification tests require a person to name a smell from a list of choices. The University of Pennsylvania Smell Identification Test (UPSIT) is a common example, using a 40-item “scratch-and-sniff” booklet where the person chooses the correct scent from four options. A shorter 12-item version, the Brief Smell Identification Test (B-SIT), is also used for quicker screenings.
Odor threshold testing aims to find the lowest concentration of an odorant that a person can detect. A substance, often n-butanol, is presented in increasing dilutions, and the point where the person first perceives the scent is their detection threshold. This test assesses the sensitivity of the olfactory receptors.
Odor discrimination tests evaluate the ability to tell different smells apart. A person is presented with three scent devices, two with the same odor and one that is different, and their task is to identify the distinct one. This process is repeated to assess the brain’s ability to differentiate smells.
The Olfactory Testing Procedure
Patients are asked to refrain from eating, smoking, or drinking anything but water for an hour before the test. This prevents strong substances from interfering with the perception of test odors.
The testing process itself is straightforward and non-invasive. A clinician administers the test using materials like a “scratch-and-sniff” booklet or odor-dispensing pens. The patient scratches a panel, sniffs it, and selects the correct odor from multiple-choice options. The procedure is painless and does not take long.
The patient follows instructions and provides their best guess for each odor, even if it is not clearly perceptible. This forced-choice method is standard and helps produce a quantifiable score.
Interpreting Test Results
After the test, the raw score of correct answers is calculated. The score is then compared to a database of results from healthy individuals, accounting for the patient’s age and sex. This normative data allows the score to be classified.
A score within the normal range for one’s age and sex is classified as normosmia, indicating a healthy sense of smell. A score below the normal range suggests a reduced ability to smell, a condition known as hyposmia. A very low or zero score indicates anosmia, the complete inability to detect odors.
Some tests, like the UPSIT, are also designed to help identify potential malingering, or the feigning of smell loss. The statistical probability of scoring below a certain threshold by chance is so low that such a result can suggest a non-genuine effort. The test result is one piece of data that a provider uses with a physical exam, medical history, and other tools to form a diagnosis and treatment plan.