A blood test that indicates if someone is at high risk of developing Alzheimer鈥檚 disease went on sale to the public in the US on 31 July. It could give people an early warning about their deteriorating health, perhaps allowing them to take preventative measures, says the manufacturer, . But some doctors are urging caution, saying the science is still too uncertain and a positive result could cause people great distress for no real benefit.
The test is based on a protein called amyloid, which is thought to build up in the brain over many years before people see symptoms of Alzheimer鈥檚, such as memory loss and confusion. In the past couple of years, two drugs consisting of antibodies that bind to amyloid have shown promise in slowing the deterioration seen with the condition 鈥� although the effect is small and there are concerns about side effects.
Researchers have long investigated whether amyloid levels could also give clues about disease progression. People can鈥檛 receive the antibody treatments unless they have a brain scan that shows amyloid clumps, known as plaques, or a test of their spinal fluid that shows excess amyloid. More recently, several firms including Quest have begun offering blood tests for amyloid to doctors. A common version measures the ratio of one form of the protein to another, as a low number indicates more brain plaques. The ratio tends to fall below a certain level about six years before plaques in the brain reach concerning levels, .
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Quest is the first firm to let members of the public order the test themselves. In theory, they can only do this if they are at a higher risk of Alzheimer鈥檚 and under the oversight of an online doctor, but in practice they can be bought by anyone aged 65 or over or anyone above 18 who ticks a box saying they have experienced symptoms, have a family history of Alzheimer鈥檚 or have ever had a head injury. Realistically, anyone who wants to pay $399 for the test can take it, says , a neurologist at the National Institutes of Health in Maryland, who isn鈥檛 connected with Quest.
When asked if this was the case, a Quest spokesperson said: 鈥淥ur website at聽questhealth.com explains that the test is not a diagnostic test and that it is for individuals who meet certain criteria, such as family history of AD, experiencing mild cognitive impairment or past head trauma or injury.鈥�
The dilemma is what people do if they get a positive result. When doctors such as Thambisetty order the test, they do so for people who already have symptoms and the result is considered alongside other investigations to help guide diagnosis. There are few details available yet on how informative this test is for people who have no Alzheimer鈥檚 symptoms.
When contacted by 快猫短视频, Quest provided a brief summary of a conference presentation about the test鈥檚 accuracy. The firm says that fuller results will eventually be published in a peer-reviewed journal. But, for now, we don鈥檛 know what proportion of people with a positive result and no symptoms end up being diagnosed with Alzheimer鈥檚 in five or 10 years鈥� time, simply because these tests haven鈥檛 been around long enough. 鈥淲e don鈥檛 know how meaningful these results are to someone without overt cognitive impairment,鈥� says Thambisetty.
It is also likely that a positive result would be a huge psychological blow 鈥� and there is little that people could do to act on the results. In its , Quest said that interventions to stall or mitigate Alzheimer鈥檚 may be most effective when begun in the early stages of the condition. But the new amyloid-based drugs can鈥檛 be given to people who have no cognitive impairment.
Quest also says people can adopt a healthier lifestyle to reduce their risk of progressing to dementia, for instance by starting a new exercise regime. It is true that exercise is recommended as a preventative measure against dementia by many medical bodies, such as England鈥檚 . But any benefit is likely to be small, as aspects of lifestyle as a whole 鈥� including diet, smoking status and other factors, as well as exercise levels 鈥� have previously been calculated to contribute only 40 per cent of people鈥檚 total risk of developing dementia. No randomised trial 鈥� the best kind of medical evidence 鈥� has yet shown that people with a positive amyloid blood test who do more exercise or adopt any other healthier habits can delay disease progression.
There are other concerns. In the US, people who get a positive result may find that it makes it harder for them to get health insurance or life insurance cover. Prospective employers could also find out about the results, potentially putting them off hiring someone.
Of course, the same is true for all medical tests that indicate someone has a serious health condition, but in those other cases, a positive test result has the benefit that, once forewarned, people can receive treatment. This wouldn鈥檛 be the case for anyone without symptoms who gets a positive amyloid blood test.
Quest says it has no plans yet to launch this test outside of the US, but research teams all over the world are working to develop similar blood tests for Alzheimer鈥檚, having been galvanised by the new antibody treatments. For instance, a group of UK medical charities recently announced new funding for such research in a project called the .
鈥淲e do want to see blood tests that can be used in the clinic to help diagnose Alzheimer鈥檚 disease,鈥� says Si芒n Gregory at the UK鈥檚 Alzheimer鈥檚 Society. She adds, however: 鈥淚t would be concerning if people could access blood tests that identify them as high risk of Alzheimer鈥檚 disease at home, and then be potentially left alone with a frightening result.鈥� Quest says it will put people in touch with a doctor to discuss the results and that a doctor will proactively contact any individual who receives a positive result.
Research into amyloid levels in the brain, spinal fluid and blood is clearly聽a promising area, but many uncertainties remain, says Thambisetty. 鈥淗ow are people going to be able to handle those results? How will people alter their behaviour? I鈥檓 not sure we have the answers.鈥�
