Blood tests for Alzheimer’s diagnosis are on the rise. At the same time, the need for Alzheimer’s biomarkers is increasing in order to make the correct diagnosis in a larger number of cases. The next steps also include establishing clear guidelines on how an Alzheimer’s blood test can be used in clinical practice, preferably by introducing these tests first in specialist care and then in primary care.
Highly accurate blood tests for Alzheimer’s disease are moving closer to use in doctors’ surgeries. New research suggests they could revolutionize the accuracy of diagnosis and provide a cleaner, faster way to participate in research and treatment. Dementia is often underdiagnosed – and when it is diagnosed by a doctor, many people are still unaware or uninformed of their diagnosis, according to the Alzheimer’s Disease Facts and Figures 2024 report. Blood tests for Alzheimer’s diagnosis are showing in research that they could significantly improve accuracy and physician confidence and provide greater accessibility and a platform for improved communication. The most promising blood tests for detecting Alzheimer’s-related changes in the brain measure phosphorylated tau protein (p-tau), an Alzheimer’s biomarker that can build up before patients show signs of cognitive impairment. The increase in the specific marker p-tau217 over time correlates with the deterioration of cognitive abilities and brain atrophy. The p-tau217 test also predicts the likelihood of amyloid plaques in the brain, which are another biomarker for Alzheimer’s disease and target recently approved treatments.
“Blood tests that (a) have greater than 90% accuracy in large populations and (b) are more widely available, promise to improve and potentially redefine the clinical trial recruitment process and the diagnosis of Alzheimer’s disease,” said Dr. Maria C. Carrillo, Chief Science Officer and Director of Medical Affairs for the Alzheimer’s Association. “While primary and secondary care physicians should currently use a combination of cognitive tests and blood tests or other biomarkers to diagnose Alzheimer’s disease, blood tests have the potential to increase the accuracy of early diagnoses and maximize the chance of accessing Alzheimer’s treatments as early as possible for better outcomes.” When considering the use of a blood test, the Alzheimer’s Association Appropriate Use Recommendations for Blood Biomarkers in Alzheimer’s Disease should be carefully followed. To help healthcare professionals incorporate blood testing for Alzheimer’s into their clinical practice, the Association has convened a panel of clinical and professional experts and is leading the development of clinical practice guidelines for the use of blood biomarkers in Alzheimer’s disease.
Study supports blood tests
A large study shows that blood tests can detect Alzheimer’s disease better than general practitioners and specialists using conventional diagnostic methods. In the study, 1213 patients were tested with the PrecivityAD2 test (known as APS2). It uses a combination of the ratio of phosphorylated to non-phosphorylated tau217 in plasma (known as %p-tau217) and the ratio of two types of amyloid (Aβ42/Aβ40) and significantly outperformed clinicians in this study. In 698 patients examined in memory clinics, APS2 was able to identify Alzheimer’s disease with an accuracy of around 90%, while the specialists’ accuracy was 73%. In 515 patients examined by primary care physicians, APS2 accuracy was also around 90%; primary care physicians identified Alzheimer’s disease 63% of the time. The researchers found that the APS2 test was also highly accurate in patients with comorbidities, such as kidney disease, which is common in older patients. “These are the results of blood samples sent in for analysis every two weeks by general practitioners, which is in line with routine clinical practice,” said lead author Sebastian Palmqvist, M.D., Ph.D., of Lund University, Lund, Sweden. “These results are particularly impressive considering that older people in primary care often suffer from diseases that can affect or alter p-tau217 concentrations.”
Focus on early diagnosis
Including people in earlier stages of Alzheimer’s disease in clinical trials could potentially help identify treatments that are effective. A study found that p-tau217 blood tests could be a simple and accurate screening tool for identifying cognitively unimpaired patients who are likely to have amyloid beta plaques in their brains. The researchers analyzed samples from 2718 cognitively unimpaired participants from 10 different studies. They found that p-tau217 in plasma can positively predict (with a range of 79-86%) the likelihood that a cognitively unimpaired person would also test positive for amyloid beta pathology on an amyloid PET scan or CSF biomarker. When the results of the amyloid beta CSF test or an amyloid beta PET scan are added to the analysis after a positive blood sample, the positive prediction improves to 90% or more. “If these numbers hold up and are replicated and confirmed by other independent laboratories, this approach could reduce the need for lumbar punctures and PET scans for Alzheimer’s diagnosis by 80 or even 90%,” said Gemma Salvadó, Ph.D., lead author of the study and associate researcher at Lund University. The results suggest that p-tau217 positivity in plasma alone may be sufficient to select cognitively unimpaired, amyloid-positive participants for many clinical trials.
Source: Alzheimer’s Disease Blood Tests Could Improve Diagnosis in Primary Care, Speed Recruiting for Research and Reduce Wait Times. AAIC 2024.
Congress: Alzheimer’s Association International Conference (AAIC)
InFo NEUROLOGIE & PSYCHIATRIE 2024; 22(4): 32 (published on 26.8.24, ahead of print)
