Diagnosis of Alzheimer's disease remains a challenge for doctors, who rely on a combination of mental and physical examinations to detect the condition. In a new study, researchers describe how a smell test could enhance the accuracy of an Alzheimer's diagnosis.

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Researchers suggest that a smell test could boost the accuracy of an Alzheimer's diagnosis.

Principal investigator David R. Roalf, Ph.D. - an assistant professor in the Department of Psychiatry at the University of Pennsylvania School of Medicine - recently reported new findings in the Journal of Alzheimer's Disease.

Alzheimer's disease is a neurological disorder characterized by memory problems and changes in behavior. It is the most common form of dementia, accounting for around 60-80 percent of all dementia cases in the United States.

According to the Alzheimer's Association, around 5.4 million people in the U.S. are living with the disease, and every 66 seconds, one more person develops it.

At present, there is no single test for the diagnosis of Alzheimer's. Doctors make a diagnosis through a series of assessments, including physical and neurological examinations, mental state tests, blood tests, brain imaging, and an evaluation of medical history.

Previous studies have suggested that sense of smell diminishes with Alzheimer's; as such, researchers have increasingly investigated whether a sniff test could be used to detect the disease.

A study reported by Medical News Today in November, for example, revealed how a series of olfactory tests effectively pinpointed patients with Alzheimer's, and researchers found that patients with a reduced sense of smell were more likely to have brain abnormalities associated with the disease.

The new study from Roalf and team offers support to such research, after finding that a sniff test boosted the diagnostic accuracy for Alzheimer's disease and mild cognitive impairment (MCI), which is considered a precursor to Alzheimer's.

Smell test enabled more accurate diagnosis of Alzheimer's, MCI

To reach their findings, Roalf and colleagues enrolled 728 older adults, of whom 292 were healthy, 262 had Alzheimer's disease, and 174 had MCI.

Participants' sense of smell was tested using the Sniffin' Sticks Odor Identification Test (SS-OIT), which required them to identify 16 different odors. Subjects also underwent standard cognitive testing.

The researchers assessed the accuracy of cognitive testing alone for the diagnosis of Alzheimer's and MCI, as well as in combination with the SS-OIT.

The team found that the SS-OIT significantly increased diagnostic accuracy for patients; cognitive testing alone diagnosed MCI with 75 percent accuracy, but this increased to 87 percent when SS-OIT was included.

Similar results were seen for the diagnosis of Alzheimer's disease, and the team says that the SS-OIT even helped to identify which patients had more advanced forms of MCI.

"These results suggest that a simple odor identification test can be a useful supplementary tool for clinically categorizing MCI and Alzheimer's, and even for identifying people who are at the highest risk of worsening."

David R. Roalf, Ph.D.

Plans for future research

While larger dementia clinics have already started using smell tests as a diagnostic tool for Alzheimer's disease in older adults, Roalf notes that the most accurate tests tend to take a long time to administer, which could be discouraging their widespread use.

As such, he and his colleagues plan to create a faster, simplified smell test for Alzheimer's diagnosis.

"We're hoping to shorten the Sniffin' Sticks test, which normally takes 5 to 8 minutes, down to 3 minutes or so, and validate that shorter test's usefulness in diagnosing MCI and dementia - we think that will encourage more neurology clinics to do this type of screening," says Roalf.

Additionally, the researchers plan to study whether protein markers of Alzheimer's - which can be found in the brain region that is responsible for sense of smell - can be identified in nasal fluid. This, the team says, could enable earlier detection of the disease.

Read how a protein in urine may increase the risk of dementia.