PHILADELPHIA — new research showed.
Accurate early diagnosis of Alzheimer’s disease is important because two monoclonal antibodies donanemab (Kisunla) and lecanemab (Leqembi) are now approved by the Food and Drug Administration (FDA) for early-stage Alzheimer’s disease. However, the use of these agents requires amyloid confirmation.
A key finding of the study was that primary care physicians had a diagnostic accuracy of 61%, and dementia specialists had an accuracy of 73%, after completing standard clinical evaluations and before seeing results of the blood test or other Alzheimer’s disease biomarkers, while the blood test used in the study had an accuracy of 91% for correctly classifying clinical, biomarker-verified Alzheimer’s disease.
“This underscores the potential improvement in diagnostic accuracy, especially in primary care, when implementing such a blood test,” said study investigator Sebastian Palmqvist, MD, PhD, associate professor of neurology at Lund University, Lund, and a consultant at Skåne University Hospital, Malmö, Sweden. “It also highlights the challenges in accurately identifying Alzheimer’s disease based solely on clinical evaluation and cognitive testing, even for specialists.”
The findings were presented at the 2024 Alzheimer’s Association International Conference (AAIC) and simultaneously published online in JAMA.
The study included two cohorts from primary and secondary care clinics in Sweden. Researchers analyzed plasma samples together at one time point in a single batch.
It also included two cohorts from Swedish primary and secondary care clinics where the plasma samples were analyzed prospectively (biweekly) in batches throughout the enrollment period, which more closely resembles clinical practice.
Primary care physicians and dementia specialists documented whether they believed their patients had Alzheimer’s disease pathology, basing the diagnoses on the standard evaluation that includes clinical examination, cognitive testing, and a CT scan prior to seeing any Alzheimer’s disease biomarker results.
They reported their certainty of the presence of Alzheimer’s disease pathology on a scale from 0 (not at all certain) to 10 (completely certain).
Plasma analyses were performed by personnel blinded to all clinical or biomarker data. Mass spectrometry assays were used to analyze Abeta42, Abeta40, phosphorylated tau 217 (p-tau217), and non–p-tau217.
Biomarkers used in the study included the percentage of plasma p-tau217, which is the ratio of p-tau217 relative to non–p-tau217, and the Abeta42 to Abeta40 ratio (the amyloid probability score 2 [APS2]). Researchers determined p-tau217 alone and when combined with the APS2.
The study included 1213 patients with cognitive symptoms — mean age 74.2 years and 48% women. Researchers applied biomarker cutoff values to the primary care cohort (n = 307) and the secondary care cohort (n = 300) and then evaluated the blood test prospectively in the primary care cohort (n = 208) and the secondary care cohort (n = 398).
The blood biomarker cutoff value was set at 90% specificity for Alzheimer’s disease pathology (the 1 cutoff-value approach). A 2 cutoff-value approach (using 1 upper and 1 lower cutoff value) was also used with values corresponding to 95% sensitivity and 95% specificity.
The primary outcome was presence of Alzheimer’s disease pathology. A positive finding of the Abeta biomarker was defined according to the FDA-approved cutoff value (≤ 0.072). A positive finding of the tau biomarker was defined as a p-tau217 level > 11.42 pg/mL in cerebrospinal fluid.
Researchers calculated the positive predictive value (PPV), negative predictive value (NPV), and diagnostic accuracy, as well as area under the curve (AUC) values.