False Elevations in Plasma P-tau 217
False elevations in plasma p-tau 217 are primarily caused by pre-analytical errors, assay-related factors, and biological confounders rather than true disease processes, with the most critical issues being improper blood collection/handling, use of low-performing assays, and comorbid cardiovascular/cerebrovascular disease.
Pre-analytical Sources of False Elevation
Blood Collection and Processing Errors
Systematic errors can occur from differences in blood collection timing (morning versus evening samples), which may artificially alter p-tau217 measurements 1
Using lithium heparin plasma instead of EDTA plasma can introduce systematic measurement differences that falsely elevate or alter p-tau217 values 1
Blood draw devices and processing parameters during collection can interfere with AD biomarker measurements and should be carefully standardized 1
Improper centrifugation or failure to remove particulates before analysis can affect measurement accuracy 1
Delayed processing or improper storage of samples may impact results, though p-tau217 is relatively robust to pre-analytical delays compared to other biomarkers 2
Analytical Sources of False Elevation
Assay Performance Issues
Not all p-tau assays perform equally, and lower-performing assays can produce misleading results that appear falsely elevated 3, 1
Random error from assay variability can result in false classification, especially for individuals with biomarker values close to diagnostic cut-offs 1
Systematic error related to changing assay conditions (new lot of antibodies or calibrators) can shift measurements and create false elevations 1
Lack of proper calibration curves, quality control performance, or plate adjustments using bridging samples can introduce measurement drift over time 1
Different assays return vastly different numerical values for the same analyte due to different calibrators and technical platforms, which can be misinterpreted as elevated when comparing across platforms 1
Biological Confounders
Medical Comorbidities
Cerebrovascular disease and cardiovascular disease are the most important biological confounders that may influence p-tau217 measurements and require careful interpretation 1, 3, 2
Age, creatinine levels, and depressive symptoms are biological confounders that can affect p-tau217 measurements 3, 2
Renal dysfunction (reflected by elevated creatinine) may alter clearance or metabolism of tau proteins, potentially affecting plasma levels 2
Critical Pitfalls to Avoid
Clinical Context Matters
In real-world clinical settings with heterogeneous populations, performance may not match research cohorts where high accuracies were recorded, as community prevalence of AD pathology is much lower 1
False positives are more likely when testing unselected populations versus highly selected research cohorts that had prior CSF or neuroimaging confirmation 1
Cognitively intact older adults can have elevated Aβ levels (and potentially p-tau), but not all will progress to dementia due to resilience factors 1
Assay Selection is Critical
High-performing platforms must be used to ensure accurate results, including Quanterix Simoa, Lumipulse G (FDA-approved for p-tau181), IP-MS methods, and emerging NULISA technology 2
Head-to-head comparisons show commonly used assays with lower performance compared to validated platforms 1
A two-cutpoint approach may be necessary to minimize false positives, with some results falling into an indeterminate zone requiring confirmatory testing 4
Quality Control Measures
Laboratory Standards
Assay performance metrics must be disclosed, including calibration curve R-values, linearity range, limit of detection, repeatability, and intermediate precision 1
Bridging samples or quality control samples should be used to account for batch variation when samples are analyzed continuously rather than in single batches 1
Certified reference materials should be employed to mitigate between-assay bias and improve comparability across platforms 1