A review challenges the performance of the FDA-cleared Lumipulse G plasma p-tau217/Aβ1−42 ratio for Alzheimer’s diagnosis, arguing the metric shows “flaws” in practice. Researchers Christian Griñán Ferré, Mercè Pallàs, and Rafael Franco of the University of Barcelona describe issues affecting interpretation and raise concerns about overreliance on a single ratio for diagnostic decisions. The critique matters for commercial diagnostics because the test is positioned as an accessible alternative for identifying Alzheimer’s biology without invasive sampling. If the ratio’s constraints are validated across populations and clinical contexts, it could reshape how laboratories and clinicians use the assay in screening and triage. The report highlights the continuing gap between analytical clearance and real-world clinical utility as the market grows for blood-based Alzheimer’s diagnostics.