Blood tests for Alzheimer’s disease are here

last month, US Food and Drug Administration consent A new blood test to help diagnose Alzheimer’s disease. The Elecsys pTau181 device, made by Roche, measures the concentration of a specific molecule — a phosphorylated form of the protein tau — in the blood. Tau is one of two proteins, the other being amyloid, that becomes misshapen and accumulates in the brains of patients with certain types of dementia. It is believed that the accumulation of these proteins interferes with communication between brain cells, leading to symptoms in these patients.

The test already received authorization in July for marketing in Europe and is therefore the first early screening system for Alzheimer’s disease to be used in approved primary care settings in the two major pharmaceutical markets on the planet. It’s the beginning of what will soon be a crowded field, as many other tests are in advanced stages of testing and approval.

How do such tests work?

Elecsys pTau181 searches blood plasma for a form of the protein tau that has a phosphate group attached to it, which is often found in elevated amounts in Alzheimer’s patients. This molecule is an indirect marker of amyloid plaques and tau neurofibrillary tangles observed in the brains of patients with the disease.

Some other tests are also approved, but not for early screening. They are evaluating other biomarkers that relate to these two proteins. One test, called Lumipulse and made by the Japanese company Fujirebio, looks at the ratio between another form of phosphorylated tau (pTau217) and part of the main protein that forms amyloid plaques (amyloid beta peptide 1-42).

The bottom line is that these tests provide clues that amyloidosis may be present in the brain, which then needs to be more accurately diagnosed using more invasive tests, such as positron emission tomography (PET) and cerebrospinal fluid analysis by lumbar puncture, which is considered the clinical gold standard for diagnosing amyloid pathology in living patients. However, even these come with a certain degree of uncertainty; True diagnostic certainty can only be obtained through postmortem brain autopsy.

Why approve these tests now?

In the past, confirming a diagnosis of Alzheimer’s disease was not that important, as there were no medications or treatments that could change the course of the disease. But with Approval of new monoclonal antibody treatments for Alzheimer’s diseaseThe landscape has changed in the past few years.

To use these drugs, you need a way to ascertain which patients can benefit from them. Since drugs work best when used early in the development of the disease, a relatively inexpensive and minimally invasive diagnostic test would be extremely beneficial. It is not practical to subject all elderly people with suspected symptoms of cognitive decline to PET scans and cerebrospinal fluid sampling, which is where a blood test for Alzheimer’s comes in.

How useful are these tests?

Elecsys pTau181 is the first test to be approved for use as a community screening tool. The idea is for it to be given at the primary care level, for example, by your primary care doctor or general practitioner. The test has been shown to have good “negative predictive value,” that is, it is effective in accurately indicating who no You have amyloid disease. In settings where the overall prevalence of amyloid disease is low, a negative result from this test is 97.9 percent reliable. This makes it useful to select which patients will be offered further testing.

The results are similar to those of other tests already approved in recent months, such as Lumipulse from Japanese company Fujirebio, which in trials showed a negative predictive value of about 97 percent.

However, there are important limitations to note: for all blood tests for Alzheimer’s disease, a relatively large proportion of patients (15-30 percent common estimate) fall into a gray area of ​​uncertainty, where specific biomarker levels do not allow for a positive or negative answer.