Information about Tests to Help Diagnose Alzheimer's

Two laboratory tests, called the ADmark Assays, can aid in the diagnosis of Alzheimer's disease. One of these assays measures beta-amyloid and tau protein in the cerebrospinal fluid (and therefore requires a spinal tap). Its use is currently discouraged because its accuracy is equivalent to that of a careful clinical evaluation, which should be conducted anyway.

The second test identifies which variation of APOE the person carries. The test assesses the probability that a person's dementia stems from Alzheimer's disease on the basis of whether the APOE ε4 variation is present. The test is not definitive because some individuals with this allele will never develop Alzheimer's. This test is not part of a routine evaluation of people with dementia.

Some people without dementia request testing for their APOE type, but this is discouraged for several reasons. First, the presence of an APOE ε4 allele indicates only that the person is at increased risk for developing Alzheimer's disease, not that he or she will definitely develop it.

Second, a panel of experts assembled by the National Institutes of Health recommended against testing for the APOE ε4 gene because, at this point, no preventive treatment or cure is available for Alzheimer's. Furthermore, awareness of the gene's presence could cause the person unnecessary anxiety or lead to discrimination by employers or health insurance companies.

Researchers are examining several simple tests to predict the risk of Alzheimer's. One promising example is a smell test. The sense of smell begins to deteriorate early in the course of the disease, often many years before other symptoms arise.

Researchers have found that people who are unable to identify more than two out of 10 common odors (such as lemon, smoke, and leather) are nearly five times more likely to be diagnosed with Alzheimer's disease in the ensuing years than people who perform better on the test. The "sniff test" will require further research, but in a large study it performed as well as memory tests and better than MRI scans in predicting which people would go on to develop Alzheimer's disease.

Publication Review By: Peter V. Rabins, M.D., M.P.H.

Published: 10 Mar 2011

Last Modified: 23 Jun 2011