A blood test—the amyloid probability score 2 (APS2)—demonstrated up to 92% diagnostic accuracy for Alzheimer's disease (AD), outperforming traditional clinical evaluations in both primary and secondary care settings, according to a recent study.

Researchers evaluated the diagnostic accuracy of the APS2—which combines the ratio of plasma phosphorylated tau 217 (p-tau217) to non-p-tau217 with the amyloid-β 42 to amyloid-β 40 ratio—for detecting AD in primary and secondary care settings.

The study, results of which published in JAMA, involved 1,213 patients with cognitive symptoms. The average age of participants was 74.2 years, with a standard deviation of 8.3 years, and 48% of the participants were women. AD pathology was found in 50% of the patients in both primary and secondary care assessments.

Using the APS2 in the primary care cohort resulted in a positive predictive value (PPV) of 91% (95% confidence interval [CI] = 87%–96%) and a negative predictive value (NPV) of 92% (95% CI = 87%–96%). In the secondary care cohort, the PPV was 88% (95% CI = 83%–93%) and the NPV was 87% (95% CI = 82%–93%).

The APS2 demonstrated a diagnostic accuracy range of 88% to 92% for detecting AD pathology. This performance was higher than the diagnostic accuracy of dementia specialists (73%) and primary care physicians (61%) who used standard clinical evaluations without AD biomarkers. In primary care, the APS2 achieved a diagnostic accuracy of 91%.

The diagnostic accuracy of the APS2, at 90% (95% CI = 88%–92%), was comparable to that of the percentage of p-tau217 alone, which also had an accuracy of 90% (95% CI = 88%–91%).

The study highlighted the potential clinical application of APS2, particularly in primary care settings, where accessible and reliable biomarker tools are often limited. The APS2 could streamline the diagnostic process and support timely treatment initiation, which is significant, given the approval of antiamyloid immunotherapies for early symptomatic AD that require biomarker-positive test results.

The prospective analysis of plasma samples confirmed the consistency of APS2's performance in clinical settings across primary and secondary care cohorts.

Full disclosures can be found in the published study.