One key front in the battle against Alzheimer's is early detection of the disease. Breakthroughs in this area could open up more treatment options that are less imposing on the patient, and researchers have just reported a promising advance in the form of a blood test that could reveal signs of Alzheimer's long before more obvious symptoms appear.

A common characteristic of Alzheimer's disease is the buildup of sticky proteins in the brain called amyloid beta. The relationship between these brain plaques and the decline in cognitive function is still unclear, but their regular presence in Alzheimer's patients has provided scientists in pursuit of early diagnoses a highly promising lead.

Advanced MRIs and new nanometer-sized biosensors are two examples of devices that could one day zero in on the early signs of Alzheimer's, as are new kinds of blood tests. Last year, scientists at Rowan University developed a blood test that could detect early-stage Alzheimer's with 100 percent accuracy, at a point when treatments are more likely to be beneficial. That blood test remains a work in progress, with the scientists moving to replicate their results in larger trials. The latest breakthrough comes from researchers at Washington State University in St Louis.

The team is aiming to develop a blood-based screening test that can reveal if amyloid beta has started building up. At present, the only way to detect these proteins is once they have already taken hold in the brain through PET scans or sampling spinal fluid, methods that are either expensive or invasive.

Earlier research has shown that the amount of amyloid beta in the blood doesn't necessarily correlate with levels in the brain, so the team shifted their attention to three amyloid subtypes, the peptides amyloid beta 38, 40 and 42. The study involved 41 subjects aged 60 or older.

Signs of cognitive impairment were detected in 23 of these, and PET scans and spinal fluid samples had confirmed either amyloid plaques in the brain or altered levels in the cerebrospinal fluid. The remaining 18 subjects had no buildup of amyloid beta.

The researchers took 20 blood samples from each subject and used mass spectrometry to measure the levels of the three amyloid beta subtypes, hoping to find a correlation with amyloid levels in the brain. And find an indication they did, with the levels of amyloid beta 42 consistently 10 to 15 percent lower than amyloid beta 40 in people with amyloid plaques in the brain.

"Amyloid plaques are composed primarily of amyloid beta 42, so this probably means that it is being deposited in the brain before moving into the bloodstream," said Randall J. Bateman, the study's senior author. "The differences are not big, but they are highly consistent. Our method is very sensitive, and particularly when you have many repeated samples as in this study — more than 500 samples overall — we can be highly confident that the difference is real. Even a single sample can distinguish who has amyloid plaques."

The researchers say that they could identify people with amyloid plaques with 89 percent accuracy when they averaged out the ratios of amyloid beta 42 and 40 across the 20 samples.

"Our results demonstrate that this amyloid beta blood test can detect if amyloid has begun accumulating in the brain," says Bateman. "This is exciting because it could be the basis for a rapid and inexpensive blood screening test to identify people at high risk of developing Alzheimer's disease."

The research was published in the journal Alzheimer's and Dementia.