measures to assess the ability to taste

The tools assessing the ability to taste (and smell) are often based on validated perception thresholds. Generally, a difference is made between detection ability, identification ability, and discrimination ability. The detection ability can be tested by assessing the absolute threshold, the lowest concentration at which a stimulus can be detected, but not yet recognized. The  recognition threshold  is the concentration at which the stimulus can not only be detected but can also be recognized. The differential threshold, or discrimination threshold,  is the level at which an increase (or decrease) in a detected stimulus can be perceived, and says something about the sensitivity or discriminative ability.

taste tests

For testing taste capability, water solutions with different concentration of taste-substances are often used. The ability to taste sweetness is usually measured with sucrose concentrations (table sugar), sourness with citric acid, saltiness with NaCl (table salt), bitterness to quinine or caffeine, and umami to MSG (mono-sodium glutamate). The cut-off values used for lowered taste perception may differ considerably between groups of individuals and for different tastes. Thresholds for bitter and sour tastants are considerably lower than those for other flavors. The detection threshold for some sweeteners is also lower compared to sucrose, for example that of intensive sweeteners. 

As you may understand preparing (fresh) taste solutions is very labor-intensive and not very practical in many (clinical or home) situations. One example of an easier taste assessment test is the Taste Strip Test. In this test, people are given paper strips with different intensities of the five basic tastes. Participants need to identify the taste of each strip. If they correctly identify more than eleven strips, they are not considered to have a loss of taste. If they identify fewer correctly it may indicate a taste disorder.

SMELL TESTS

Different tests exist to identify smell ability of a person.^[1] Three examples of such smell tests are:

1. The University of Pennsylvania Smell Identification Test (UPSIT). This test consists of a booklet with 40 scratch and sniff strips. The person being tested scratches each strip one at a time to release the scent. A potential participant can smell and select one out of four choices listed next to the strip. The total score is the number of odors correctly identified. The score is then compared against reference data to determine olfactory function.
2. The European Test of Olfactory Capabilities (ETOC ). This test is a comprehensive method for evaluating a person’s sense of smell. The odorants used in the tests are typically presented in pen-like dispensers and represent different aspects of olfactory function. The participant is presented with the odorants one at a time and is asked to identify the aroma. This can be done in a multiple choice option or open question. With this test also detection thresholds can be measured, that is the smallest concentration that someone can detect reliably. For discrimination testing, two pens are smelled and it is questioned whether the odor is different. The score is then compared against reference data to determine olfactory function. The odors comprise of a range of common food odors, such as coffee, mint, orange, vanilla, but also non-food such as rose, leather, smoke and gasoline.
3. The ‘Sniffin’ Sticks’ smell test, that uses pen-like devices that release odors. It includes three parts: testing how well you can detect smells, tell different smells apart, and identify specific odors. The scores for each part range from 0 to 16, and the total score can range from 0 to 48. A score of 30 or above indicates a normal sense of smell, a score between 16-30 indicates a reduced sense of smell, and a score below 16 indicates loss of smell ability.

In order to test smell capability of children there is an adjusted smell test for kids. This test contains smells that are child-friendly, such as bubble gum, strawberry, chocolate and banana. Different references values exist depending on the age and the developmental stage of the child. 

Smell tests can also be used to identify early indicators of different diseases, for example Parkinson’s or Alzheimer’s disease. Sometimes, self-reported loss of of smell can also be used as an indicator for disease, for example in COVID-19.