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The use of a blood test significantly improved diagnostic accuracy compared with standard clinical evaluations for Alzheimer disease, especially in primary and secondary care settings.
Sebastian Palmqvist, MD, PhD
(Credit: Lund University)
In a new study presented at the 2024 Alzheimer’s Association International Conference, July 28 to August 1, in Philadelphia, Pennsylvania, use of the PrecivityAD2 (C2N Diagnostics) test was able to detect Alzheimer disease (AD) with high accuracy among patients who presented with cognitive symptoms compared with traditional diagnostic methods in primary and secondary care settings.1 The blood test, known as Amyloid Probability Score-2 (APS2), uses a combination of plasma phosphorylated-tau217 to not-phosphorylated-tau217 ratio (%p-tau217) and the ratio of 2 types of amyloid (Aβ42/Aβ40).2
After a standard work-up, clinicians in primary care accurately identified AD in 58% of patients compared with 89% (83–95%) for APS2 (P <.001). Notably, dementia experts had a diagnostic accuracy of 74% (69–80%) in comparison with 90% (86–94%) for APS2 (P <.001). In primary care, 51% of patients tested positive for AD. For diagnosis, 25% had subjective cognitive decline (SCD), 47% had mild cognitive impairment (MCI), and 28% had dementia. In secondary care, 49% of patients were AD pathology positive and diagnoses were 21% for SCD, 43% for MCI, and 36% for dementia.
“Notably, these were the results of blood samples that have been shipped bi-weekly for analysis from primary care units, which is similar to routine clinical practice,” lead author Sebastian Palmqvist, MD, PhD, an associate professor of neuroscience at Lund University in Sweden, said in a statement.2 “These results were especially impressive considering that older populations in primary care often have medical conditions that can influence or vary the concentrations of p-tau217.”
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In the study, investigators included 940 prospective and unselected patients who sought medical assessment for early cognitive symptoms. Researchers measured plasma %p-tau217 and Aβ42/40 utilizing mass spectrometry and APS2, and then calculated the combination of these values. Authors established predefined cutoffs in an independent training cohort and applied them to primary (n = 307) and secondary care (n = 300) cohorts, which comprised of patients who undergone cognitive evaluation where plasma samples were evaluated in single batches. The blood test was then assessed prospectively in patients from primary (n = 100) and secondary (n = 234) care where researchers analyzed plasma samples bi-weekly. The main outcome of the study was amyloid status as established by cerebrospinal fluid AD biomarker positivity.
In single batch analyses, the area under the curve (AUC) for APS2 was 0.97 (95% CI, 0.95–0.99), positive predictive values (PPV) 91% (87–96%), and negative predictive values (NPV) 92% (87–96%) in primary care. In secondary care, the AUC was 0.96 (0.94–0.98), PPV 88% (83–93%), and NPV 87% (82–93%). When investigators had the samples analyzed prospectively in primary care, the AUC was 0.97 (0.95–1.00), PPV 90% (81–99%), and NPV 90% (82–98%). Then in secondary care, the AUC was 0.97 (0.94–0.99), PPV 92% (86–97%), and NPV 89% (83–94%).
“We see this as a major step towards global clinical implementation of an Alzheimer blood test,” senior author Oskar Hansson, MD, PhD, full professor of neurology at Lund University, said in a statement.2 “It highlights the need for Alzheimer biomarkers in making a correct diagnosis more of the time. The next steps include establishing clear guidelines for how an Alzheimer blood test can be used in clinical practice, preferably by implementing these tests first in specialist care and then in primary care. This work is currently ongoing.”
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