eGFR Threshold for Accurate Plasma p-Tau217 Testing
Based on the most recent high-quality evidence, plasma p-tau217 maintains diagnostic accuracy for detecting Alzheimer's disease pathology down to an eGFR of approximately 45-60 mL/min/1.73 m², with significant interference occurring below eGFR <45 mL/min/1.73 m².
Evidence-Based Threshold Recommendations
The 2026 multicenter study by the UGOT/Roche consortium 1 provides the most definitive guidance on this question. This study analyzed 2,571 participants and demonstrated that:
- Standard single cutoffs showed reduced accuracy in chronic kidney disease (CKD), dropping from baseline accuracy to 0.65 (95% CI: 0.57-0.72) in patients with eGFR <60 mL/min/1.73 m²
- Optimized cutoffs improved accuracy to 0.83 (95% CI: 0.76-0.89) in the CKD group
- Advanced CKD (eGFR <45 mL/min/1.73 m²) showed even more pronounced effects on p-tau217 levels
Practical Clinical Algorithm
For eGFR ≥60 mL/min/1.73 m²:
- Use standard p-tau217 cutoffs without adjustment
- Results are reliable for clinical decision-making
For eGFR 45-59 mL/min/1.73 m² (CKD Stage 3a):
- P-tau217 remains usable but requires platform-specific optimized cutoffs 1
- Consider using p-tau217/Aβ42 ratio instead of absolute p-tau217 values, as ratios are less affected by kidney function 2
- A double-cutoff strategy may be warranted to reduce false classifications
For eGFR <45 mL/min/1.73 m² (CKD Stage 3b or worse):
- Exercise significant caution - kidney dysfunction substantially elevates plasma p-tau217 levels 2, 3
- Strongly prefer ratio-based measures (p-tau217/Aβ42 or p-tau217/BD-tau) which show stable performance across all eGFR groups 2, 4
- Consider alternative diagnostic pathways (CSF biomarkers or amyloid PET) for definitive diagnosis
Key Mechanistic Insights
The 2026 ALZAN cohort study 2 revealed critical findings:
- All individual plasma biomarkers were significantly elevated in eGFR <60 group
- Age-adjusted analysis confirmed inverse correlation between eGFR and plasma biomarkers
- Kidney dysfunction impaired specificity of p-tau181, GFAP, NfL, and BD-tau (p<0.001)
- P-tau217 alone was less affected than other biomarkers, but still showed influence
- Ratio-based measures (especially p-tau217/Aβ42) maintained stable sensitivity and specificity across all eGFR groups
The Norwegian Norfrail study 3 demonstrated that eGFR explained 27% of plasma p-tau217 variance (p<0.001), underscoring the substantial confounding effect of kidney function.
Platform-Specific Considerations
Recent 2026 evidence 5 confirms that while different automated platforms (Lumipulse G600II and Cobas e801) show excellent analytical concordance (ICC=0.922), they require platform-specific thresholds. This is particularly important when kidney function is impaired, as systematic concentration differences between platforms may compound interpretation challenges.
Common Pitfalls to Avoid
- Do not ignore mild-to-moderate CKD (eGFR 45-60): Even stage 3a CKD affects p-tau217 interpretation
- Do not use standard cutoffs in advanced CKD: This leads to false-positive results
- Do not rely solely on absolute p-tau217 values when eGFR <60: Ratios are more reliable
- Do not forget to measure eGFR before interpreting p-tau217 results - this is a mandatory prerequisite
Optimal Testing Strategy
When ordering p-tau217 testing:
- Always obtain concurrent serum creatinine to calculate eGFR using CKD-EPI equation 6
- If eGFR <60 mL/min/1.73 m²: Request ratio-based reporting (p-tau217/Aβ42 or p-tau217/BD-tau) 2, 4
- If eGFR <45 mL/min/1.73 m²: Consider confirmatory testing with CSF biomarkers or amyloid PET imaging
- Document kidney function in the clinical interpretation to guide future longitudinal comparisons 7
The evidence strongly supports that ratio-based plasma biomarkers overcome the confounding effects of reduced kidney function 2, making them the preferred approach when eGFR falls below 60 mL/min/1.73 m².