Introducing a New Blood Test for Alzheimer’s Disease: Essential Information You Should Know.

With the aging population, incidents of Alzheimer’s disease are escalating. In the U.S., 7.2 million Americans aged over 65 are expected to be living with Alzheimer’s by 2025, and the percentage of affected individuals rises with age. Around 5% of those aged 65 to 74 are afflicted with Alzheimer’s disease.

After confirming cognitive impairment, doctors can utilize blood tests as a less invasive alternative to traditional diagnostic methods for Alzheimer’s disease. Previously, comprehensive diagnostic techniques included invasive and costly procedures like positron emission tomography (PET) scans and lumbar punctures to extract cerebrospinal fluid, alongside MRI or CT scans to diagnose other cognitive impairments.

The new blood tests analyze the ratio of two proteins in the blood, which correlates with the presence of amyloid plaques—a significant marker for Alzheimer’s disease in the brain.

For individuals experiencing memory issues potentially associated with Alzheimer’s, the initial step is to consult a primary care physician (PCP) for cognitive evaluations. If cognitive impairment is indicated, the patient will then be referred to a neurologist for a thorough analysis.

Experts in dementia and PCPs concur that this blood test can facilitate diagnosis, as emphasized by Dr. Greg Day, a neurologist at the Mayo Clinic in Jacksonville, Florida. Dr. Day led a study on the blood test published in June in the Journal of the Alzheimer’s Disease Association. Research published in 2024 in Jama found the test equally effective for confirming suspected Alzheimer’s diagnoses, whether ordered by a PCP or a specialist.

PCPs can use the test results to refer patients to specialists who can prescribe treatments like Rekanemab and Donanemab. Dr. Day noted that PCPs may also prescribe drugs like donepezil, which aids cognitive function in Alzheimer’s patients. The FDA’s approval is believed to facilitate Medicare and private insurance coverage for the new blood tests, according to Dr. Day.

The test, known as the “lumipulse g ptau217/ß-amyloid 1-42 plasma ratio,” is intended for individuals aged over 55 who exhibit signs of cognitive decline, as identified by clinicians. It is designed for the early detection of amyloid plaques linked to Alzheimer’s disease. (Amyloid plaques are abnormal clusters found between brain cells, composed of beta-amyloid protein.)

Related: A man at high risk for early-onset Alzheimer’s still grapples with the disease in his 70s – how does this happen?

Early detection is critical, according to Dr. Sayad Osim Ajitzi, Clinical Director of Behavioral Neurology and Memory Impairment at Yale School of Medicine. He likens the Alzheimer’s brain to a rusty engine, where the plaque acts like rust, impairing the engine’s function, explaining that “the buildup hinders its ability to run smoothly.”

There are FDA-approved treatments that work similarly to motor oil, keeping the engine running, though they do not eliminate the plaque itself. He stated that available treatments can slow cognitive decline by approximately 30% to 40%, allowing patients to maintain their function longer.

“If you’re currently driving and living independently, you might not be able to do so in five years if you’re on no treatment,” Ajitzi points out. “With medication, that span could extend from five years to eight years.” By integrating these blood tests into practice, more individuals could gain access to effective treatments sooner.

Current recommendations do not support testing as a general screening method for the entire population. These tests are intended strictly for individuals showing symptoms of Alzheimer’s disease as determined by healthcare professionals.

Although amyloid presence is somewhat common during typical aging, it does not necessarily predict future Alzheimer’s disease development. Dr. Ajitzi explains that detecting amyloid plaques two decades prior to cognitive symptoms would render immediate treatment impractical.

“Treatment isn’t completely without risks,” he added. Receiving lecanemab involves biweekly infusions and is followed by maintenance doses every four weeks. Donanemab is administered every four weeks and may lead to side effects such as headaches, nausea, and vomiting.

In rare instances, donanemab can elicit potential life-threatening allergic reactions, and both medications have been associated with rare occurrences of brain swelling and bleeding—known as “amyloid-related imaging abnormalities,” observable in brain scans.

The new blood tests may produce false positives—indicating Alzheimer’s disease when it is not present. This occurs because the amyloid markers sought by the tests can also arise from other health conditions. For instance, the accumulation of amyloid in the brain might suggest suboptimal kidney function, prompting Dr. Day to recommend kidney function tests alongside Alzheimer’s blood tests.

The Mayo Clinic study evaluated around 510 participants, with 246 exhibiting cognitive decline. The blood tests confirmed that 95% of those with cognitive concerns had Alzheimer’s disease. However, 5.3% of results returned false negatives, while 17.6% evidenced false positives, according to Dr. Day.

Many false-positive cases still displayed Alzheimer’s-like changes in their brains, but their symptoms were actually due to other conditions, such as Lewy body dementia. The Mayo study highlights that blood tests can help clinicians differentiate Alzheimer’s from other types of dementia.

As with numerous clinical studies, test populations generally consist of individuals in better health than average, often with insurance and being primarily white and non-Hispanic, as pointed out by Dr. Day. Consequently, in broader applications of these blood tests, individuals with conditions such as sleep apnea or kidney disease might also test positive without having Alzheimer’s. Some individuals with these ailments may exhibit memory issues or cognitive declines unrelated to Alzheimer’s disease. If a blood test suggests amyloid buildup, additional tests can be mandated, and patient history can assist in ruling out other causes.