Smelly testing

Improbable research reports on a test for Alzheimer's using peanut butter. 

“Results. The mean odor detection distance of AD patients’ left nostril (5.1 cm), and not their right (17.4 cm), was significantly less (F(3,90) = 22.28, p < 0.0001) than the other groups…. “Conclusion. This non-invasive and inexpensive left–right nostril odor detection test appears to be a sensitive and specific test for probable AD.”

actually, losing smell sensitivity is a traditonal way to test for early dementia, including HIV related dementia. This is why testing for smell is part of the neurological exam.  Usually we tested by opening a small bottle full of coffee grounds, but this webpage suggests using soap for some reason.

On the other hand, as this BMJ article notes: Hardly anyone does it nowadays in routine exams.

Abstract

When was the last time you asked a patient about their sense of smell? When did you last perform any test of smell identification? Probably never is the answer to both questions. And if you ever did, I expect it was an afterthought and you had to send the clinic nurse scurrying off for an orange or some coffee grains, or worse still you dug out those prehistoric smell bottles that are more appropriate for reviving the dead than assessing the rhinencephalon (the smell brain). Ammonia is useful for cleaning metal. Tinct. asafoetida – the smell of flatus – is an important ingredient of one of the Pentagon’s most repugnant smells ‘US Government Standard Bathroom Malodor’, which causes volunteers to scream and curse within a few seconds...

Loss of smell is called anosmia, and the reason we rarely do the testing is that there are so many reasons for it that testing doesn't give you a lot of information.
LINK from webMD:

Nasal congestion from a cold, allergy, sinus infection, or poor air quality is the most common cause of anosmia. Other anosmia causes include:

• Nasal polyps -- small noncancerous growths in the nose and sinuses that block the nasal passage.
• Injury to the nose and smell nerves from surgery or head trauma.
• Exposure to toxic chemicals, such as pesticides or solvents.
• Certain medications, including antibiotics, antidepressants, anti-inflammatory medication, heart medications, and others.
• Cocaine abuse.
• Old age. Like vision and hearing, your sense of smell can become weaker as you age. In fact, one's sense of smell is most keen between the ages of 30 and 60 and begins to decline after age 60.
• Certain medical conditions, such as Alzheimer's disease, Parkinson's disease, multiple sclerosis, nutritional deficiencies, congenital conditions, and hormonal disturbances.
• Radiation treatment of head and neck cancers.

In other words, the person is more likely to suffer from a cold than Alzheimer's disease...