Use of Alzheimer's disease biomarkers in primary care

among us Previous case-based reviewsteased the opportunity to use biomarkers to increase diagnostic accuracy and convenience. alzheimer's disease (advertisement). These tests are no longer limited to research settings and are now available to specialists and primary care clinicians alike. However, I believe its greatest impact will be in our clinical space, given that most cognitive disorders are first identified in primary care.

The pathological processes associated with AD can be detected approximately 20 years before the appearance of clinical symptoms. It is estimated that the symptomatic period of cognitive impairment accounts for only the last third of the disease course of Alzheimer's disease.. Clinicians primarily use imaging studies such as PET, cerebrospinal fluid (CSF), and even blood biomarkers of beta-amyloid and tau, which are pathological factors in AD, to detect AD pathology before symptoms appear. patients with the disease can be identified. Importantly for current interventions, the application of biomarkers can also aid in early diagnosis of Alzheimer's disease.

Although amyloid PET identifies one of the earliest markers of potential AD, a common barrier to advanced imaging is cost. Medicare currently approves coverage of amyloid PET for cases of suspected cognitive impairment. A large study of more than 16,000 older adults in the United States had positive PET scans. 55.3% of cases had mild cognitive impairment (MCI). The PET positivity rate in adults with other dementias was 70.1%. Application of PET has changed care in more than 60% of patients with MCI and dementia. A quarter of participants had their diagnosis changed from AD to another dementia, and 10% had their diagnosis changed from another dementia to AD.

Fluid biomarkers may include cerebrospinal fluid or blood samples. To date, CSF testing has provided more consistent results and defined protocols for evaluation. Still, collecting CSF is more difficult than collecting blood, and patients and their families may object to lumbar puncture. Therefore, evaluation of CSF generally remains the domain of experts and research centers.

Primary care clinicians have been waiting for a reliable blood-based biomarker for Alzheimer's disease, but the wait may be over. a Research to be published in July 2024 The study included 1,213 adults being screened for cognitive symptoms in Sweden. They completed a test that measures the ratio of phosphorylated tau-217 to non-phosphorylated tau-217, with and without a serum amyloid ratio test. These tests were compared with the clinician's clinical diagnosis and CSF results, which are considered the gold standard.

When using clinical tools alone, primary care clinicians and specialists had diagnostic accuracy for MCI and dementia of only 61% and 73%, respectively. These values ​​were substantially weaker compared to the performance of either the serum tau ratio or the amyloid ratio (both 90% accurate). The authors concluded that serological testing has the potential to improve clinical care for patients with cognitive impairment.

Where does that leave us today? Currently, blood biomarkers are commercially available that use a variety of test values ​​and cutoff values. Although these may be helpful, they are likely difficult to compare and interpret for primary care clinicians. Additionally, these tests are less likely to be covered by insurance. Amyloid PET scans are a very reasonable option to enhance clinician judgment regarding suspected cognitive impairment, but not all geographic areas have ready access to this imaging test.

Still, it is a great time to have more objective tools at our disposal to distinguish between MCI and AD. These tools can only be optimized by clinicians who recognize the symptoms and perform the necessary baseline testing to determine the pretest probability of MCI or dementia.