This past Sunday, a group of researchers reported in the journal, Nature Medicine, a preliminary technique that uses variation in blood levels of 10 fats to predict the likelihood that elderly individuals would develop mild cognitive impairment (MCI) or Alzheimer’s Disease in the following 2-3 years. The sample size was small and the results may not generalize beyond the narrow age-range and demographics of the study group (i.e. the assay is far from ready for “prime time”), but the study is an important first step towards a lower cost (vs PET imaging) and less invasive (vs spinal tap) predictive biomarker of cognitive decline*. Its publication has also triggered a flurry of discussion on possible ethical ramifications of this sort of blood biomarker. I will not attempt to address these ethical issues specifically here. Rather, I seek to highlight that how ethically troubling one views the technology to be may depend partly on the sort of knowledge one thinks these biomarkers reveal (applied epistemology at its best).