Researchers in a Journal of Molecular Medicine review argue that the FDA-cleared Lumipulse G plasma p-tau217/Aβ1−42 ratio has flaws as a blood-based Alzheimer’s diagnostic test. The paper by Christian Griñán Ferré, Mercè Pallàs, and Rafael Franco challenges how the biomarker performs across clinical and analytical contexts. The review frames the controversy around assay interpretation and diagnostic accuracy rather than rejecting the concept of plasma biomarkers. It highlights that even “first approved” tests can face scientific pushback as more data and comparative analyses emerge. For the market, the critique increases scrutiny on the next wave of plasma tau assays, especially regarding how ratios should be used for ruling in and ruling out disease in real-world settings.