News Brief: FDA-Cleared Alzheimer’s Disease Blood Test Has Many False-Positive Results

In 2025 the Food and Drug Administration (FDA) authorized the marketing of a medical device that analyzes a blood sample and determines whether amyloid plaques are present in the brain.[1] The device was cleared for adults aged 50 years or older with symptoms suggestive of Alzheimer’s disease.

Amyloid plaques are abnormal protein deposits in the brain that are found in many but not all people with Alzheimer’s disease. The Lumipulse G pTau217/ß-Amyloid 1-42 Plasma Ratio device was the first to receive FDA clearance and was discussed in the November 2025 edition of Worst Pills, Best Pills News.[2] Subsequently, the FDA cleared several similar devices.[3]

False-positive results associated with the device were one of its main risks. Such results can lead to anxiety and unnecessary treatment, as well as discrimination in health insurance, long-term care insurance or retirement communities.[4]

A 2026 cross-sectional study, published in JAMA Neurology, confirmed that the Lumipulse device has variable results, including many false-positive results.[5] The study involved two cohorts. For participants in the first cohort (n=252), the presence of amyloid plaques was confirmed through spinal fluid samples collected via a lumbar puncture (spinal tap) or PET scans. Participants in the second cohort (n=101) had a parent with a history of Alzheimer’s disease, and amyloid plaques were confirmed via PET scans.

In cohort 1 the Lumipulse device identified most participants with amyloid plaques correctly, with a sensitivity ranging from 98% to 100%, but the ability to correctly identify those without amyloid plaques (specificity) ranged from only 23% to 84%. In the second cohort the test’s sensitivity ranged from 88% to 99% and its specificity from 85% to 96%.

The researchers speculated that the device’s variability reflected the performance of the reagents used for the analysis of the blood samples. The storage conditions of blood samples and certain medical conditions, such as kidney disease, may also affect the accuracy of this and similar tests.[6]

The study’s results confirm that the Lumipulse device has limited clinical value for diagnosing Alzheimer’s disease. In addition to false-positive results, there is insufficient evidence that brain amyloid plaques cause Alzheimer’s disease or that early diagnosis and treatment in asymptomatic patients is beneficial.

References

[1] First FDA-cleared blood test for amyloid plaques in the brain has limited clinical uses. Worst Pills, Best Pills News. November 2025. https://www.worstpills.org/newsletters/view/1694. Accessed September 4, 2026. 

[2] First FDA-cleared blood test for amyloid plaques in the brain has limited clinical uses. Worst Pills, Best Pills News. November 2025. https://www.worstpills.org/newsletters/view/1694. Accessed September 4, 2026.

[3] George J. FDA clears blood test to detect Alzheimer's in primary and specialty care. Medpage Today. August 25, 2026. https://www.medpagetoday.com/neurology/alzheimersdisease/122742. Accessed September 4, 2026. 

[4] Smith DG. Blood tests to predict Alzheimer’s are causing confusion and distress. The New York Times. August 12, 2026. https://www.nytimes.com/2026/08/12/well/mind/alzheimers-disease-blood-tests-prediction.html. Accessed September 4, 2026.

[5] Algeciras-Schimnich A, Bornhorst JA, Figdore DJ, et al. Variability in clinical performance of the FDA-cleared Lumipulse P-Tau217/β-Amyloid 1-42 Plasma Ratio. JAMA Neurol. 2026;83(8):823-827. 

[6] Smith DG. Blood tests to predict Alzheimer’s are causing confusion and distress. The New York Times. August 12, 2026. https://www.nytimes.com/2026/08/12/well/mind/alzheimers-disease-blood-tests-prediction.html. Accessed September 4, 2026.