New Alzheimer’s blood tests may be game-changers for treating the disease

By Robert Langreth | Bloomberg

There’s no simple way to tell who has Alzheimer’s disease, but with a blockbuster treatment for millions of Americans on the horizon, blood-test makers are gearing up to change this.

Even doctors who were initially skeptical about blood tests for the condition are gaining confidence that products from Quest Diagnostics Inc., Quanterix Corp. and C2N Diagnostics can help distinguish which patients may qualify for treatment with the experimental drug lecanemab, expected to be approved next year. The drug is the first ever to clearly slow the progress of Alzheimer’s, the brain-wasting disease that affects some 6 million Americans.

“These tests are getting better — not perfect, but accurate enough so they will be used,” says Harvard Medical School neurologist Reisa Sperling. Sperling was unsure about the tests a few years ago, she says, but now is convinced they are almost ready for widespread use. “They are simpler than a PET scan, they are simpler than a spinal tap.”

Studies suggest that amyloid – an abnormal brain protein targeted by lecanemab – is present in more than two-thirds of Alzheimer’s patients and around half of 10 million more with mild cognitive impairment. Convenient testing could have a huge impact on how the therapy, a collaboration between Eisai Co. and Biogen Inc., is used. The drug must be infused into patients every two weeks with potential side effects that include brain swelling and bleeding.

It’s also likely to be expensive: sales could hit $10 billion over time, according to RBC Capital Markets analysts. Doctors won’t want to risk administering it to patients without proof of amyloid in their brains.

To qualify for lecanemab initially, patients would likely need a brain PET scan or a spinal tap to show amyloid is present. The scans could be hard to get: Medicare has restricted coverage of amyloid PET scans that can cost as much as $7,000 — most hospitals perform them only occasionally. Spinal taps are another way to get tested, but they’re invasive and sometimes painful, so some patients shy away.

Early Stages

Testing people promptly will be important: Eisai’s drug works only for people in the early stages of Alzheimer’s. While it slowed the rate of cognitive decline by 27% over 18 months, doctors hope that the impact could broaden over time. Potential side effects include brain swelling and brain bleeding, and the drug is likely to be expensive. Doctors won’t want to risk administering it to patients who don’t have amyloid in their brains.

A few years ago, blood tests for Alzheimer’s seemed like a distant prospect, but researchers are making rapid advances. Some tests compare levels of different forms of amyloid protein found in the blood, which can indicate what’s present in the brain. Others monitor various forms of a second protein called tau that tends to rise in the blood when amyloid is present. None are routinely covered by insurers or cleared by the Food and Drug Administration.

Founded by scientists from Washington University in St. Louis, C2N introduced its first amyloid blood test in 2020. The panel costs $1,250 and combines amyloid levels with measurements of another Alzheimer’s-linked protein called apolipoprotein E4 and the patient’s age to predict risk. Last month, C2N said it would start selling an improved version of the test that also measures one of the tau proteins.

Quest introduced a $500 amyloid-ratio blood test back in April. It’s covered by some insurance plans, and the company’s exploring a combination test for additional Alzheimer’s proteins. Quanterix began selling a blood test this year for one form of tau protein and is working with Eli Lilly & Co. on another.

Some researchers say the tests are mainly useful for narrowing down the number of people who need scans or spinal-fluid tests. Many have only been used to evaluate samples from people in clinical trials, who are often younger, less diverse and have fewer pre-existing conditions than the general population with Alzheimer’s symptoms, says Michelle Mielke, an epidemiologist at the Wake Forest University School of Medicine.

“The field is moving so fast,” she says, but the blood tests “are not good enough right now to be used as a sole diagnostic.”

Mielke and Sperling served on a panel of experts convened by the Alzheimer’s Association that said in July that the blood tests could be used in symptomatic people at specialized memory clinics. Still, they said, more data are needed before the tests are ready for use in primary care.

“The big question is whether you can use them instead of a PET scan” or spinal-fluid test, says Kaj Blennow, a clinical testing expert at the University of Gothenburg in Sweden. “I am not convinced.”

Some tests can be thrown off by drugs taken by people with heart failure, or by obesity, Blennow says. But in the future, the tests may help primary care clinics or smaller hospitals identify people who should be sent on to specialists for more definitive testing, he says.

In a presentation at a recent Alzheimer’s meeting, University of Southern California researchers said an assay similar to C2N’s second-generation test was 88% accurate in identifying healthy people with high levels of amyloid in the brain. While there were still some false positives, the test could be useful for determining whether people qualify for prevention trials, they said, reducing the number of health people who would need PET scans by almost two-thirds.

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