A simple odor identification test or a sniff test can help identify people at risk of developing Alzheimer's disease because the sense of smell declines sharply in its early stages.
The researchers found the test useful for diagnosing a pre-dementia condition called mild cognitive impairment (MCI), which often progresses to Alzheimer's dementia within a few years.
‘A simple odour identification test can be a useful supplementary tool for clinically categorising MCI and Alzheimer's, and even for identifying people who are at the highest risk of worsening.’
"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 Roalf, Assistant Professor at Perelman School of Medicine at the University of Pennsylvania in the US.
Roalf and his colleagues used a simple, commercially available test known as the Sniffing Sticks Odor Identification Test, in which people must try to identify 16 different odours.
They administered the sniff test, and a standard cognitive test (the Montreal Cognitive Assessment), to 728 elderly people.
The participants had already been evaluated by doctors and had been placed in one of three categories -- healthy older adult, mild cognitive impairment, or Alzheimer's dementia.
Roalf and his team used the results from the cognitive test alone, or combined with the sniff test, to see how well they identified participants in each category.
The sniff test added significantly to diagnostic accuracy when combined with the cognitive test, the researchers reported in the study published in the Journal of Alzheimer's Disease.
For example, the cognitive test alone correctly classified only 75 per cent of people with MCI, but that figure rose to 87 percent 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 MCI and Alzheimer's, and even for identifying people who are at the highest risk of worsening," Roalf said.
Neurologists have been eager to find new ways to identify people who are at high risk of Alzheimer's dementia but do not yet show any symptoms.
There is a widespread consensus that Alzheimer's medications now under development may not work after dementia has set in.