'Sniff test' can help diagnose early Alzheimer's: study

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David R. Roalf, Ph.D.
David R. Roalf, Ph.D.

Administering a simple “sniff test” can enhance the accuracy of diagnosing Alzheimer's disease and the mild cognitive impairment that often progresses to dementia, according to the results of a study published in the Journal of Alzheimer's Disease.

“There's the exciting possibility here that a decline in the sense of smell can be used to identify people at risk years before they develop dementia,” said principal investigator David R. Roalf, Ph.D., an assistant professor at the Perelman School of Medicine at the University of Pennsylvania.

Roalf and coauthors administered the Montreal Cognitive Assessment as well as the commercially available Sniffin' Sticks Odor Identification Test, in which subjects must try to identify 16 different odors, to 728 older adults who already had been evaluated by physicians and had been categorized as being healthy, having mild cognitive impairment or having Alzheimer's dementia. The researchers used the results from the cognitive test alone, or combined with the sniff test, to see how well they identified subjects in each category.

They found that the sniff test added significantly to diagnostic accuracy when combined with the cognitive test. For example, the cognitive test alone correctly classified only 75% of people with mild cognitive impairment, but that figure increased to 87% when the sniff test results were added. Combining the two tests also enabled more accurate identification of healthy older adults and those with Alzheimer's dementia. The combination even boosted accuracy in assigning people to milder or more advanced categories of mild cognitive impairment.

“These results suggest that a simple odor identification test can be a useful supplementary tool for clinically categorizing mild cognitive impairment and Alzheimer's, and even for identifying people who are at the highest risk of worsening,” Roalf said.

Prior studies have linked a weakening sense of smell to Alzheimer's disease, but use of the sniff test has not become widespread because the tests that seem most useful take five to eight minutes to administer, according to the researchers. Roalf and colleagues now are trying to develop a test that can be administered in three minutes but work as well as current ones.

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