Currently, assessment for Alzheimer’s disease includes using brain scans and cognitive function tests. While these help give a probable diagnosis of Alzheimer’s, there may be doubts that it is another type of dementia. A blood test that can help distinguish Alzheimer’s would be of great use toward a proper diagnosis.
Usefulness of a Blood Test
Various compounds elevated in the brains of people with Alzheimer’s can be measured in cerebrospinal fluid, or CSF. This may help with a diagnosis, but the process of gathering CSF involves a great deal of discomfort for the patient. Having a blood test that can help with diagnosing Alzheimer’s disease would spare a patient this, be more practical for healthcare providers, and add to the battery of tests already in use.
Current Blood Tests
Taking blood is routine when assessing a person with Alzheimer’s. However, these tests do not investigate the disorder itself, but are used to rule out other problems that may cause cognitive deficits such as changes in levels of certain hormones, glucose and vitamins, or infectious diseases such as syphilis and HIV.
Testing Substances From the Brain
Levels of the protein amyloid beta increase in the brains of Alzheimer’s patients. There are two main types: AB40 and AB42, with the disc-like plaques that are a hallmark of Alzheimer’s, mainly containing AB42. Normally, amyloid beta is secreted into the CSF and blood; Richard Mayeux showed in “Neurology” November 2003 edition that Alzheimer’s subjects had high AB42 plasma levels pre-disease and large AB42 decreases with disease onset. In contrast, Marieke van Oijen reporting in “Lancet Neurology” August 2006 edition found high pre-disease AB40 associated with an increased Alzheimer’s risk. Ongoing studies are investigating if these markers can help in evaluating the risk of developing Alzheimer’s.
Proteins involved in inflammation and cell death are elevated in the brain and plasma of Alzheimer’s patients, leading to the possibility that increasing levels of these could be used for assessing the degree of damage occurring as Alzheimer’s progresses.
Testing Substances From the Blood
Amyloid beta may be cleared from the brain by immune cells called macrophages, a process defective in Alzheimer’s, possibly due to malfunctioning plasma immune cells. Hripsime Avagyan showed in the “Journal of Neuroimmunology” May 2009 edition that while none of a group of high functioning elderly people had defective plasma immune cells, 93 percent of those with Alzheimer’s did, thus testing for these cells could help distinguish people with Alzheimer’s.
Another possible blood test is the use of techniques that can evaluate large amounts of genetic material or proteins in the blood with the hope of finding some that can distinguish those with possible Alzheimer’s.
Difficulties With Testing
Many of the aforementioned blood tests have some difficulties associated with them. For instance, not all investigations have found differences in blood amyloid beta levels in Alzheimer’s compared to other dementias, so it may not be useful for distinguishing between disorders. Testing blood inflammatory components may prove difficult as levels can also increase during an infection. Similarly, defective macrophages also occur in people who are highly stressed, thus this test may only be used for ruling out this disease when people don’t have defective macrophages, as opposed for ruling it in if they do.
References
- “Canadian Medical Association Journal”; Diagnosis and Treatment of Dementia: 2. Diagnosis; Howard Feldman et al; March 2008
- “Neurology”; Plasma AB40 and AB42 and Alzheimer’s Disease: Relation to Age, Mortality, and Risk; Richard Mayeux et al; November 2003
- “Lancet Neurology”; Plasma AB1-40 and AB1-42 and the Risk of Dementia: a Prospective Case-Cohort Study; Marieke van Oijen et al; August 2006
