FDA clears first blood test for Alzheimer's disease

The FDA has approved the first blood test for Alzheimer's disease based on a blood test – from Fujirebio – in a step forward for early diagnosis.

The test, dubbed the Lumipulse G pTau217/ß-Amyloid 1-42 Plasma Ratio, is intended for use in adults 55 and older who are showing early signs and symptoms of Alzheimer's dementia, according to an FDA statement.

It measures two proteins in blood plasma, pTau217 and β-amyloid 1-42, and calculates the ratio between them, which the regulator said can indicate the presence in the brain of amyloid plaques – a hallmark of Alzheimer's – even though the test doesn't measure amyloid directly.

Improved diagnostic options could be a boost to the new generation of amyloid-targeting therapies – Eisai/Biogen's Leqembi (lecanemab) and Eli Lilly's Kisunla (donanemab) – which have been held up as the first disease-modifying therapies for Alzheimer's but so far have yet to make much headway in the marketplace. Sales of the two drugs were $86 million and $21.5 million, respectively, in the first three months of the year.

The blood test offers an alternative to PET scans, which can detect amyloid plaques in Alzheimer's patients years before the onset of symptoms, as well as similar tests that measure the two proteins in the cerebrospinal fluid (CSF).

While effective, PET scans are a costly and time-consuming option, expose patients to radiation, and may not be easily accessed in some areas or for people who are under- or uninsured. CSF tests, meanwhile, require an invasive lumbar puncture, which, while generally safe, is harder to carry out than a blood test and can have complications including back pain, infection, bleeding, and rarely, nerve damage and blood clots.

Fujirebio's test has a breakthrough designation from the FDA and was approved on the strength of a clinical study involving nearly 500 patients, which mirrored the typical US demographics among Alzheimer's patients.

In the study, 91.7% of patients who tested positive using the diagnostic turned out to have amyloid plaques by a PET scan or lumbar puncture, while 97.3% of those with a negative result had the same result after confirmatory testing. Overall, less than one in five patients had an equivocal result with Fujirebio's test.

"Nearly seven million Americans are living with Alzheimer's disease, and this number is projected to rise to nearly 13 million," said Michelle Tarver, director of the FDA's Center for Devices and Radiological Health (CDRH).

"Today's clearance is an important step for Alzheimer's disease diagnosis, making it easier and potentially more accessible for US patients earlier in the disease."

The Alzheimer's Drug Discovery Foundation described the approval as a "game changer" that will make detecting patients in the early stages of this type of dementia as easy as detecting high cholesterol.

It will allow "more patients to receive treatment options that have the potential to significantly slow or even prevent the disease," said the organisation's co-founder and chief scientific officer Howard Fillit.

Image by Ahmad Ardity from Pixabay