Same Blood Samples, Different Results: ADRC Pilot Flags Alzheimer's Biomarker Lab Gap

A University of Washington Alzheimer's Disease Research Center analysis of nearly 200 paired plasma samples found that values from a national central laboratory ran consistently higher than values from the center's own lab, even though the two sets of results were strongly correlated, the National Alzheimer's Coordinating Center reported this month.

The National Alzheimer's Coordinating Center (NACC), which coordinates data across the federally funded network of Alzheimer's Disease Research Centers (ADRCs), reported on October 12, 2026, that a pilot comparison of blood biomarker results found statistically significant differences depending on where the samples were analyzed. Nearly 200 plasma samples, collected from the same participants at the University of Washington ADRC in 2023 and 2024, were split so that one portion was analyzed at the National Centralized Repository for Alzheimer's Disease and Related Dementias (NCRAD) and the other locally at the UW ADRC. According to the NACC report, results from NCRAD were consistently higher than the UW ADRC's own results, even though the two sets of measurements were significantly correlated with each other.

The work, led by Cameron Afzal, a medical student at Tufts University School of Medicine working with the UW ADRC over the summer, found that the ranking of patients held steady across both platforms: the same participants fell into the same high, middle, or low thirds for a given biomarker regardless of which lab ran the test. Afzal is quoted by NACC saying this indicates the testing kits are not necessarily producing inaccurate results, but that results from one platform are shifted systematically up or down relative to the other. The ADRC program relies on standardized clinical protocols across its member centers specifically so that data from different sites can be combined for research, and biomarker results such as these inform research classifications of mild cognitive impairment (MCI) and Alzheimer's disease in NACC's shared dataset.

According to the NACC report, Afzal and the UW ADRC cautioned that the pilot's sample size was not large enough to determine whether the lab-to-lab gap actually changes how individual participants would be classified under research diagnostic criteria for MCI or Alzheimer's disease. The finding adds to previously reported concerns within the ADRC network about combining biomarker data across sites: a separate 2024 analysis of plasma biomarker results from 14 Alzheimer's Disease Research Centers, published in Alzheimer's & Dementia, identified a cluster of unusually high amyloid ratio values traced to a single site, which affected the diagnostic accuracy of the pooled dataset until it was investigated.

NACC said further validation work involving larger sample sets is needed before the UW ADRC comparison can show whether, or how often, the measured gap between labs would change a research participant's classification.