A new blood test, recently arrived in Brazil, may help in the diagnosis of Alzheimer’s. By using a technology that identifies small molecules in blood samples, the procedure makes it possible to observe the presence of an important marker of the disease.
Alzheimer’s has symptoms such as memory loss and difficulty doing everyday activities because it is associated with a degeneration of the central nervous system.
The disease is the most prevalent type of dementia in the world. In Brazil, it affects approximately 1.2 million people and affects about 11% of the elderly population, which is the most affected by the condition.
Regarding mortality, the 2019 Global Burden of Disease (GBD) points out that Alzheimer’s along with other dementias represent a rate of 25 deaths per 100,000 inhabitants in the country.
The diagnosis is made primarily through clinical practice. In this way, the doctor investigates, in the face of symptoms and tests, if a person really has Alzheimer’s. Some research, for example, has already advanced to understand the causes of the condition in order to increase the accuracy of the diagnosis.
One of the most consolidated currents on the origin of the condition looks at two proteins that are considered markers of Alzheimer’s — that is, substances associated with the disease.
One of these proteins is beta-amyloid, which is normally found in the walls of neurons, important cells for brain function.
Rodrigo Carvalho, a neurologist at the DFVNeuro neurosurgery center and at the Sírio-Libanês Hospital, explains that, in excess, beta-amyloid is deposited in brain tissues.
“One of the hypotheses is that this protein deposit begins many years before the onset of Alzheimer’s symptoms. This already places this protein as a pathological marker of the disease”, he says.
This accumulation of beta-amyloid triggers the retention of another protein, called TAU. It is the latter that causes death of neurons and, consequently, causes a degenerative process of brain activity.
Thus, both proteins are associated with Alzheimer’s. This discovery means that “the trend is increasingly to classify the disease based on those substances that are altered”, continues the neurologist.
There are already some tools that seek to observe these two markers. One of them is the collection of cerebrospinal fluid, a liquid that permeates the region of the brain and lumbar spine. Because it is in constant contact with the region of the central nervous system, it is possible to observe the concentration of beta amyloid by the CSF.
This procedure is done by a doctor who inserts a needle between the vertebrae of the spine. Then, it is possible to remove the cerebrospinal fluid to perform an exam in order to verify the presence of beta amyloid. The lower the concentration of the protein, the greater the indication for Alzheimer’s, as this is an indication that the substance must be retained in the walls of the brain.
Even though it is a useful procedure to complement the clinical suspicions of Alzheimer’s, the CSF collection has some problems. One of them is the price – when done by a doctor, the exam is more expensive than other more common ones. Another point are some contraindications, as in the case of patients who have an infectious process on the skin or have spinal problems that make it difficult to apply the injection.
The new test, launched in the United States just over a month ago and which is made available in Brazil by the Dasa network of hospitals and laboratories, tries to overcome these impasses.
It works similarly to CSF collection by measuring beta-amyloid to see if the patient has Alzheimer’s. Because it is a blood test, however, it needed some changes that mainly rely on a technological advance called mass spectrometry.
Gustavo Campana, medical director at Dasa, explains that observing the amount of protein in the cerebrospinal fluid is simpler because the liquid is in constant contact with the brain, a region that has the highest concentration of beta-amyloid.
However, research has already observed that some proteins can pass from the cerebrospinal fluid into the blood, but in a smaller amount – a phenomenon known as the blood-brain barrier.
For this reason, a common blood test would not have the same precision in indicating the concentration of beta-amyloid as in the CSF removal procedure. Spectrometry, in this case, is used precisely because it can observe proteins, even in small amounts, in a blood sample.
“It’s a technology that allows me to separate different molecules to observe their concentration”, explains Campana.
The exam is not for everyone
While it is an important way to increase the accuracy of Alzheimer’s diagnosis, the new blood test is not for everyone.
The restriction of the procedure happens mainly because Alzheimer’s is a disease of clinical diagnosis. That is, it uses other mechanisms and also the specialist’s own assessment of the patient’s condition.
Carvalho says that magnetic resonance imaging can be used to see if the symptoms were not caused by other diseases that mimic Alzheimer’s, such as stroke.
“It’s not that everyone needs to do it, but for some specific cases, diagnostic complementation is essential”, says Campana.
One such case in which it could be useful to observe the presence of beta-amyloid is when the doctor suspects that the patient may have Alzheimer’s or frontotemporal dementia, another disease also caused by neurodegeneration.
In this impasse, Carvalho explains, it is important to have a more accurate diagnosis because treatment for Alzheimer’s can worsen frontotemporal dementia.