Amyloid probability score 2 blood test helps identify Alzheimer disease: JAMA

A new study by Sebastian Palmqvist and team showed that when used in conjunction with established cutoff values, the amyloid probability score 2 (APS2) and proportion of p-tau217 demonstrated good diagnostic accuracy for diagnosing Alzheimer disease (AD) in patients expressing cognitive symptoms in primary and secondary care. The findings of this study were published in the Journal of American Medical Association.

Due to Alzheimer's disease, 1 in 5 women and 1 in 10 males have dementia. The majority of people with cognitive symptoms are referred to tertiary care after initially being examined in primary care. Between 25% and 35% of individuals receiving treatment at specialist clinics and probably even more people receiving general care receive a false diagnosis of symptomatic Alzheimer's disease. For the treatment of people with early symptomatic Alzheimer disease, two anti-amyloid immunotherapies have been licensed, and further medicines are probably in the works. To diagnose Alzheimer's disease, primary care doctors do not have access to easily obtainable biomarker tools and so this study prospectively assessed a clinically accessible AD blood test in primary and secondary care using the predetermined biomarker cutoff values.

From February 2020 to January 2024, 1213 individuals in Sweden had clinical examinations for cognitive problems. The biomarker cutoff values were determined in an independent cohort and matched to a primary care cohort and a secondary care cohort. The plasma sample of each patient was tested prospectively in a separate batch for each cohort. Each patient provided one plasma sample for examination within two weeks after collection. The main result was AD pathology and AD in clinical terms was the secondary endpoint. The calculations were made to determine the diagnostic accuracy, area under the curve (AUC), negative predictive value (NPV) and positive predictive value (PPV).

In both primary and secondary care, the APS2 demonstrated a high degree of diagnostic accuracy (range, 88%-92%) in identifying Alzheimer disease pathology. When employing the APS2, primary care doctors had a diagnosis accuracy of 61% vs. 91%, whereas dementia experts detected clinical Alzheimer disease with a diagnostic accuracy of 73% vs. 91%. Overall, using predetermined threshold values, the APS2 and proportion of p-tau217 alone demonstrated a good diagnostic accuracy for detecting Alzheimer disease in persons with cognitive symptoms in primary and secondary care settings.

Reference:

Palmqvist, S., Tideman, P., Mattsson-Carlgren, N., Schindler, S. E., Smith, R., Ossenkoppele, R., Calling, S., West, T., Monane, M., Verghese, P. B., Braunstein, J. B., Blennow, K., Janelidze, S., Stomrud, E., Salvadó, G., & Hansson, O. (2024). Blood Biomarkers to Detect Alzheimer Disease in Primary Care and Secondary Care. In JAMA. American Medical Association (AMA). https://doi.org/10.1001/jama.2024.13855