Blood Tests for Alzheimer’s Are Here

Last month, the US Food and Drug Administration allowed A new blood test to help diagnose Alzheimer’s disease. Manufactured by Roche, the Elecsys pTau181 measures the concentration of a specific molecule – a phosphorylated form of the tau protein – in the blood. Tau is one of two proteins, the other being amyloid, that become deformed and accumulate in the brains of patients with certain types of dementia. It is believed that the formation of these proteins interferes with the communication of brain cells, resulting in symptoms in these patients.

The test already received approval for marketing in Europe in July and is thus the first early screening system for Alzheimer’s for use in primary care settings approved in the two major pharmaceutical markets of the planet. It’s an opener that will soon become a crowded field, as several other tests are in advanced stages of testing and approval.

How does this type of test work?

Elecsys pTau181 looks for a form of tau protein with a phosphate group in blood plasma, which is often found in high levels in Alzheimer’s patients. This molecule is an indirect marker of the plaques of amyloid and neurofibrillary tangles observed in the brains of patients with the disease.

Some other tests are also approved, although not for primary screening. These evaluate other biomarkers associated with these two proteins. One test, called Lumipulse and developed by the Japanese company Fujirebio, looks at the ratio between another form of phosphorylated tau (pTau217) and a key protein fragment that forms amyloid plaques (amyloid beta peptide 1-42).

The bottom line is that these tests give clues to the possible presence of amyloidosis in the brain, which then requires more invasive tests, such as PET (positron emission tomography) scans and cerebrospinal fluid analysis by lumbar puncture, which are considered the living pathology standard in clinical amyloidosis patients. Even these, however, come with some uncertainty; Accurate diagnostic certainty can only be obtained by postmortem dissection of the brain.

Why approve this test now?

In the past, confirming the diagnosis of Alzheimer’s disease was not so important, because there were no drugs or therapies that could change the course of the disease. But with Approval of a new Alzheimer’s monoclonal antibody treatmentThe landscape has changed over the past few years.

To use these drugs, you need a way to determine which patients might benefit. And since drugs ideally give the best results when used early in the disease’s progression, relatively inexpensive and minimally invasive diagnostic tests would be extremely useful. It is impractical to subject all elderly people with suspected signs of cognitive decline to PET scans and cerebrospinal fluid sampling, so this is where blood tests for Alzheimer’s are performed.

How useful are these tests?

Elecsys pTau181 is the first test approved for use as a community-screening tool. The idea is that it will be administered at the primary care level – so, for example, by a primary care physician or general practitioner. The test has been shown to have a good “negative predictive value”—that is, it’s effective at pinpointing no Have amyloid disease. In settings where the overall prevalence of amyloid disease is low, a negative result of this test is 97.9 percent reliable. This makes it useful for selecting which patients to put forward for further testing.

The results are similar to other tests already approved in recent months, such as LumiPulse from Japan’s Fujirebio, which showed a negative predictive value of about 97 percent in the test.

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