Blood test can now detect Alzheimer's disease before symptoms appear

Understanding the biomarker breakthrough

Cognitive decline can now be detected through a simple blood test, marking a shift from dismissing memory lapses as normal aging to treating them as biological changes worthy of clinical attention. Current diagnostic guidelines increasingly rely on biomarkers, primarily proteins such as amyloid and tau measured in the bloodstream, to identify Alzheimer's disease before it progresses. Blood tests focus on protein levels, specifically p-tau217, p-tau181 and amyloid-beta 42, with recent international studies indicating that blood tests for p-tau217 can approach the accuracy of lumbar puncture or amyloid PET scans in detecting Alzheimer-related changes, according to Dr. Shea Yat-fung, a geriatrician and dementia specialist.

Amyloid proteins clump into plaques in the brain, while abnormal tau proteins form tangles inside brain cells, disrupting neural communication. In Hong Kong, immunology-related techniques are the most commonly used methods for measuring these disease-related proteins because the systems are smaller and more automated. Specialists generally recommend having these blood tests performed at specialist outpatient clinics.

When testing makes sense

The key requirement for these blood tests is that the person truly shows signs of cognitive problems, for example, mild cognitive impairment or dementia, rather than routine screening of everyone. At the primary-care level, doctors screen for cases using memory tests and a review of medical history, with blood tests and other diagnostic methods recommended when the diagnosis is uncertain. If a primary-care blood test for p-tau217 yields a high negative predictive value, it is very likely the person does not have Alzheimer's disease, prompting clinicians to investigate other causes of cognitive problems.

Doctors use statistical methods to set thresholds, choosing an upper cut-off and a lower cut-off. Results above the upper cut-off are considered positive, and results below the lower cut-off are considered negative, with values falling between forming a grey zone. International guidelines aim to keep the grey zone fairly small, typically 10 to 20 percent of tested people, meaning at most about one in five patients will get an indeterminate result requiring further follow-up.

The scale of the problem

Nearly 22 percent of people aged 60 and over in Hong Kong have mild neurocognitive disorder or mild cognitive impairment, and close to 10 percent meet criteria for major neurocognitive disorder (dementia), according to a recent community-based study by the Chinese University of Hong Kong. Globally, 75 percent of people living with dementia receive no formal diagnosis at all, and those who do frequently face wait times of up to two years for diagnostics.

Prevention through lifestyle

When combined with managing blood pressure and cholesterol alongside lifestyle measures, including a balanced diet, regular physical activity, social engagement, quitting smoking, and addressing sensory problems such as hearing or vision loss, some studies report that development of dementia may be prevented or delayed by 40 percent.

Source: South China Morning Post