First FDA-Cleared Blood Test for Amyloid Plaques in the Brain Has Limited Clinical Uses

In May 2025 the Food and Drug Administration (FDA) authorized the marketing of a medical device that analyzes a blood sample and concludes from this analysis whether amyloid plaques are present in the brain. The device is for adults aged 50 years or older who show symptoms of Alzheimer’s disease.[1]

Amyloid plaques are abnormal protein deposits in the brain that are found in many but not all people with Alzheimer’s disease. Although similar blood tests are already on the market, the Lumipulse G pTau217/ß-Amyloid 1-42 Plasma Ratio device is the first to be cleared by the FDA.[2]

The FDA-cleared device analyzes a blood sample to determine the concentrations of two proteins called pTau217 and ß-amyloid 1-42. The device then calculates the ratio of these two proteins in blood plasma; certain values of the ratio correlate with the presence of amyloid plaques in the brain.[3]

Until recently, amyloid plaques in the brain could only be detected by analyzing cerebrospinal (spinal) fluid samples collected via a lumbar puncture (spinal tap) or amyloid positron-emission tomography (PET) scans.[4] According to the FDA, the new blood test may reduce the need for these more costly and involved tests.[5]

Alzheimer’s disease is an irreversible, progressive disease of the brain that significantly impairs thinking, memory and — in the late stages — the ability to perform basic daily activities. The cause is not fully understood, and at present there is no cure. However, because the condition is sometimes characterized by the presence of amyloid plaques in the brain, treatments that target these plaques have been developed.

A recent survey by the Alzheimer’s Association, which receives substantial financial support from industry, found that many people are not yet familiar with blood tests for Alzheimer’s disease; however, taking these tests may be viewed as a way to benefit from early treatment.[6] Although the blood tests may detect amyloid buildup in the brain, the presence of amyloid does not mean a person has Alzheimer’s disease or will develop the condition. In fact, many people with amyloid buildup will never develop dementia.[7] Moreover, signs and symptoms of cognitive decline may be unrelated to Alzheimer’s disease.

The diagnosis of Alzheimer’s disease is not based on subjective complaints of cognitive decline or the results of a diagnostic test. A clinician makes the diagnosis after a comprehensive clinical assessment. A recent Viewpoint article in JAMA Internal Medicine rightfully stated that the results of blood tests such as the Lumipulse G pTau217/ß-Amyloid 1-42 Plasma Ratio “offer little actionable insight.”[8]

About the blood test

The Lumipulse G pTau217/ß-Amyloid 1-42 Plasma Ratio test was cleared for marketing under the 510(k) pathway, which is available to manufacturers that can show that their medical device is “substantially equivalent” to another device already on the market (called a predicate).[9] For the Lumipulse G pTau217/ß-Amyloid 1-42 Plasma Ratio, the FDA accepted the manufacturer’s claim that another of the company’s tests (a test that analyzes spinal fluid samples) is such a predicate.

The FDA also reviewed data from a clinical study including 499 adults with cognitive decline. All participants had previously undergone either a spinal fluid test or PET scan for brain amyloid plaques. These results and the blood test results were compared.[10],[11] For about 20% of the participants, the blood test could not confirm either the presence or absence of amyloid plaques in the brain. For participants with a positive blood test, 91.7% had a prior positive result for brain amyloid plaques; for participants with a negative blood test, 97.3% had a prior negative result.

The main risk associated with the blood test is false-positive results, which could lead to anxiety and unnecessary treatment.[12] Similarly, because not all people with Alzheimer’s disease have amyloid buildup in their brains, even a correctly identified positive test result could mean that other treatable causes of cognitive decline (for example, vision impairment or thyroid dysfunction) will not be adequately explored.[13] A negative result could provide a false sense of reassurance and lead to patients not having further clinical evaluation of their signs and symptoms.[14] A positive test result may also lead to discrimination in employment and health insurance.[15]

Concerns for clinical practice

The FDA cautions that the cleared blood test should be used only for adult patients with signs of cognitive decline who seek treatment in specialized care settings. The agency stated that in such a context the blood test can be used in conjunction with additional tests and other patient clinical information to aid decision-making for diagnosis and treatment options.[16] The Alzheimer’s Association, which released a clinical practice guideline for the blood tests in July 2025, similarly warns that they are not an alternative to a comprehensive clinical assessment.[17] Although the guideline does not endorse specific tests, it recommends that tests (such as the one cleared by the FDA) can be used instead of spinal fluid tests or PET scans.

Due to the accessibility of blood tests, Public Citizen’s Health Research Group shares the concerns of Alzheimer’s disease experts that the tests will be widely used or will be used as a standalone diagnostic or screening tool for asymptomatic older patients. The tests will possibly replace the more time-consuming and accurate diagnostic workups needed for the diagnosis of Alzheimer’s disease.[18],[19],[20] Reliance on blood tests is of particular concern because research also has shown that the detection of amyloid plaques may lead to an increase in inappropriate use of drugs for Alzheimer’s disease.[21]

What You Can Do

There are two FDA-approved amyloid-targeting drugs: lecanemab (LEQEMBI) and donanemab (KISUNLA). Both are intended for patients with a diagnosis of mild cognitive impairment or mild dementia and confirmed amyloid buildup in the brain. Public Citizen’s Health Research Group has designated both drugs as Do Not Use.[22],[23] Evidence is lacking that early detection and subsequent treatment with amyloid-targeting drugs is beneficial.[24],[25] Moreover, these drugs are associated with serious adverse effects, such as amyloid-related imaging abnormalities that may be a precursor to severe, life-threatening brain swelling or bleeding.

The blood test cleared by the FDA is only useful for those being evaluated for Alzheimer’s disease who would otherwise need a more invasive diagnostic test as part of their clinical assessment.[26] There is insufficient evidence that brain amyloid plaques cause Alzheimer’s disease or that early diagnosis and treatment of brain amyloid plaques in asymptomatic patients is beneficial. At present, the Lumipulse G pTau217/ß-Amyloid 1-42 Plasma Ratio has very limited uses.
 

References

[1] Food and Drug Administration. FDA clears first blood test used in diagnosing Alzheimer’s disease. May 16, 2025. https://www.fda.gov/news-events/press-announcements/fda-clears-first-blood-test-used-diagnosing-alzheimers-disease. Accessed August 31, 2025.

[2] Chen E, Feuerstein A.FDA clears first blood test for diagnosing Alzheimer’s. STAT. May 16, 2025. https://www.statnews.com/2025/05/16/alzheimers-fujirebio-fda-approval/. Accessed August 31, 2025

[3] Food and Drug Administration. FDA clears first blood test used in diagnosing Alzheimer’s disease. May 16, 2025. https://www.fda.gov/news-events/press-announcements/fda-clears-first-blood-test-used-diagnosing-alzheimers-disease. Accessed August 31, 2025.

[4] Widera E, Covinsky K. The limited role of Alzheimer disease blood-based biomarkers in primary care. JAMA Intern Med. 2025 Jul 1;185(7):755-757.

[5] Food and Drug Administration. FDA clears first blood test used in diagnosing Alzheimer’s disease. May 16, 2025. https://www.fda.gov/news-events/press-announcements/fda-clears-first-blood-test-used-diagnosing-alzheimers-disease. Accessed August 31, 2025.

[6] Alzheimer’s Association. New Alzheimer’s Association report: Americans want early diagnosis, treatment and are open to risk-taking to slow disease progression. April 29, 2025. https://www.alz.org/news/2025/facts-figures-report-alzheimers-treatment. Accessed August 31, 2025.

[7] Widera E, Covinsky K. The limited role of Alzheimer disease blood-based biomarkers in primary care. JAMA Intern Med. 2025 Jul 1;185(7):755-757.

[8] Ibid.

[9] Ibid.

[10] Ibid.

[11] Food and Drug Administration. Summary. Lumipulse G pTau217/ß-Amyloid 1-42 Plasma Ratio. K242706. May 16, 2025. https://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfpmn/pmn.cfm?ID=K242706. Accessed August 31, 2025.

[12] Food and Drug Administration. FDA clears first blood test used in diagnosing Alzheimer’s disease. May 16, 2025. https://www.fda.gov/news-events/press-announcements/fda-clears-first-blood-test-used-diagnosing-alzheimers-disease. Accessed August 31, 2025.

[13] Rubin R. What to know about the first FDA-cleared blood test for Alzheimer biomarkers. JAMA. 2025 Jul 15.

[14] Widera E, Covinsky K. The limited role of Alzheimer disease blood-based biomarkers in primary care. JAMA Intern Med. 2025 Jul 1;185(7):755-757.

[15] Public Citizen. Comments on Food and Drug Administration’s Draft Guidance: “Early Alzheimer’s disease: Developing drugs for treatment” (FDA-2013-D-0077). June 7, 2024. https://www.citizen.org/wp-content/uploads/2684.pdf. Accessed August 31, 2025.

[16] Food and Drug Administration. FDA clears first blood test used in diagnosing Alzheimer’s disease. May 16, 2025. https://www.fda.gov/news-events/press-announcements/fda-clears-first-blood-test-used-diagnosing-alzheimers-disease. Accessed August 31, 2025.

[17] Alzheimer’s Association. Alzheimer’s Association releases its first clinical practice guideline for blood-based biomarker tests. July 29, 2025. https://aaic.alz.org/downloads2025/BBMCPGNewsRelease.pdf. Accessed August 25, 2025.

[18] Public Citizen. Comments on Food and Drug Administration’s Draft Guidance: “Early Alzheimer’s disease: Developing drugs for treatment” (FDA-2013-D-0077). June 7, 2024. https://www.citizen.org/wp-content/uploads/2684.pdf. Accessed August 25, 2025.

[19] Rubin R. What to know about the first FDA-cleared blood test for Alzheimer biomarkers. JAMA. 2025 Jul 15.

[20] Widera E, Covinsky K. The limited role of Alzheimer disease blood-based biomarkers in primary care. JAMA Intern Med. 2025 Jul 1;185(7):755-757.

[21] Langa KM, Burke JF. Preclinical Alzheimer disease-early diagnosis or overdiagnosis? JAMA Intern Med. 2019;179(9):1161-1162.

[22] Lecanemab for Alzheimer’s Disease: Do not use. Worst Pills, Best Pills News. October 2023. https://www.worstpills.org/newsletters/view/1556. Accessed August 31, 2025.

[23] Donanemab (KISUNLA): A bad choice for Alzheimer’s disease. Worst Pills, Best Pills News. November 2024. https://www.worstpills.org/newsletters/view/1626. Accessed August 31, 2025.

[24] Walsh S, Merrick R, Milne R, et al. Considering challenges for the new Alzheimer's drugs: Clinical, population, and health system perspectives. Alzheimers Dement. 2024 Sep;20(9):6639-6646.

[25] Public Citizen. Comments on Food and Drug Administration’s draft guidance: “Early Alzheimer’s disease: Developing drugs for treatment” (FDA-2013-D-0077). June 7, 2024. https://www.citizen.org/wp-content/uploads/2684.pdf. Accessed August 31, 2025.

[26] Ibid.