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AAIC 2024: Blood Test Shows High Accuracy in Identifying Alzheimer Disease
Diagnostic accuracy higher compared with primary care physicians and dementia specialists using clinical exam, cognitive testing, and CT scan
MONDAY, Aug. 5, 2024 (HealthDay News) -- A blood test is 90% accurate in identifying Alzheimer disease in patients with cognitive symptoms seen in either primary care or at specialized memory care clinics, according to a study published online July 28 in the Journal of the American Medical Association to coincide with the Alzheimer’s Association International Conference, held from July 28 to Aug. 1 in Philadelphia.
Sebastian Palmqvist, M.D., Ph.D., from Lund University in Sweden, and colleagues assessed whether a blood test based on the ratio of plasma phosphorylated tau 217 (p-tau217) to non-p-tau217 (expressed as percentage of p-tau217) combined with the amyloid-β 42 to amyloid-β 40 plasma ratio (the amyloid probability score 2 [APS2]) can accurately identify Alzheimer disease.
The analysis included patients undergoing cognitive evaluation in primary care (307 patients) or secondary care (300 patients). Twenty-three percent of participants had subjective cognitive decline, 44% had mild cognitive impairment, and 33% had dementia. Across both primary and secondary care, 50% of patients had Alzheimer disease pathology.
The researchers found that in the primary care cohort, when the samples were analyzed in a single batch, the area under the curve (AUC) was 0.97 when the APS2 was used, the positive predictive value was 91%, and the negative predictive value was 92%. In the secondary care cohort, the corresponding values were 0.96, 88%, and 87%, respectively. In the primary care cohort, when the plasma samples were analyzed prospectively (biweekly), the AUC was 0.96 when the APS2 was used, the positive predictive value was 88%, and the negative predictive value was 90%. For the secondary care cohort, with samples analyzed prospectively, the corresponding values were 0.97, 91%, and 91%. Across the four cohorts, the diagnostic accuracy was high (range, 88% to 92%).
In contrast, primary care physicians had a diagnostic accuracy of 61% for identifying clinical Alzheimer disease after clinical examination, cognitive testing, and a computed tomography scan versus 91% using the APS2. Compared with APS2, dementia specialists also had lower diagnostic accuracy (91% versus 73%). In the overall population, the diagnostic accuracy of using the APS2 was similar to using p-tau217 alone (90% for both).
“The blood test should not serve as a standalone diagnostic test for Alzheimer disease but must be interpreted in a clinical context,” Palmqvist told Elsevier’s PracticeUpdate. “This is important since Alzheimer pathology can be asymptomatic for many years and cognitive symptoms in some patients with Alzheimer pathology can be primarily caused by other conditions. Incorrect interpretation of a positive test could thus lead to underdiagnosis of relatively common non-Alzheimer disease conditions.”
Several authors disclosed financial ties to the pharmaceutical industry.
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