Clinical use of blood ptau217: plasma or serum? The matrix matters
Bibliographic record
Abstract
BACKGROUND: Several studies on both research and clinical cohorts have confirmed the high accuracy of plasma p -Tau217 assays in identifying individuals in the Alzheimer's disease pathway. However, it is worth noting that while these blood tests rely strictly on EDTA plasma, clinical settings and some bio-banked research environments often prefer serum matrices, as dictated by established clinical chemistry protocols for other targets. Yet, the performance of p -Tau217 assays in serum remains unclear, prompting the interest to determine if serum results are comparable to plasma. METHOD: This study evaluated the performance of six high-performing plasma p -Tau217 assays (Simoa, ALZpath/Janssen; Nulisa, Alamar; Lumipulse, Fujirebio; MSD, Lilly/S-plex) in three study-phases (Figure 1). First, p -Tau217 was quantified and compared between plasma and serum in samples of 100 participants with known amyloid PET status and ranging within the AD continuum. The second phase then assessed specific validation parameters (e.g., Precision, Parallelism, Dilution Linearity, Sample Stability) between matrices within the same assay, following standard immunoassay validation protocols. Phase III compared the impact of different plasma collection tubes (e.g., EDTA, Sodium-Citrate and Lithium-Heparin) on p -Tau217 measurements. RESULT: High correlations of ptau217 were found between plasma and serum for most assays, but plasma often yielded higher relative concentrations compared to serum, except for Lumipulse and MSD-Lilly (Figure 2). In the AD context, ptau217 could detect amyloid pathology with high accuracy in serum (0.63<AUC<0.95). However, plasma cutoffs applied in serum led to high misclassification rates. Furthermore, the reassessment of assay parameters suggest that not all assays can reliably quantify blood ptau217 in serum as they do in plasma. Lastly, ptau217 quantifications highly correlated within assays amongst plasma collection tube types (0.87<rho<0.99), although a proportional bias was detected between plasma EDTA and Citrate (Figure 3). CONCLUSION: Our data show that, when assays are reliable in serum, relative biomarker values vary across blood fractions, which most often prevents the use of a single cutoff for the two matrices. In addition, very high agreement was found between collection tube types, suggesting that ptau217 is similarly quantified regardless of the clotting factor used. However, once again the data underscores caution when merging results from samples collected under different protocols.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.030 | 0.057 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.002 | 0.000 |
| Bibliometrics | 0.001 | 0.002 |
| Science and technology studies | 0.001 | 0.002 |
| Scholarly communication | 0.005 | 0.002 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.002 | 0.002 |
| Insufficient payload (model declined to judge) | 0.003 | 0.002 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".