pTau217, plasma
Ordering Info & Methodology
Test Code
Cerner Synonyms
PTAU217B
Phosphorylated tau 217, plasma
Turn Around Time
Methodology
Analysis performed weekly
Roche Cobas Elecsys: sandwich immunoassay with electrochemiluminescent detection
Ordering Guide
Not orderable in Cerner. Not orderable in British Columbia.
Specimen Requirements
Sample Type
Collection Container
Alternate Collection Containers
EDTA plasma
Lavender (EDTA tube)
None
600 ul at minimum preferred in a 13 x 75 mm aliquot tube; Absolute minimum: 150 uL
After separation from cells: Ambient 7 days, Refrigerated 1 month, Frozen 1 month; Max freeze/thaw cycles: 6
Add on stability
This is the length of time after sample collection that this analyte is stable. Test can be added to a previously collected sample if the time since collection is less than the add on stability time.
Minimum Volume
Add On Stability
Collection and Shipping Requirements
Collect and process following standard laboratory procedures for an EDTA tube. Separate plasma from cells and aliquot into a 13 x 75 mm tube (preferred). Freeze and ship frozen.
Reference Intervals
Female Reference Interval
Age Category | Reference Interval | units |
|---|---|---|
Male Reference Interval
Age Category | Reference Interval | units |
|---|---|---|
Additional Notes
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Measurement Uncertainty (MU)
Every laboratory value is an estimate of the true concentration of substance. MU is the 95% confidence interval around that estimate. 95% of the time, the true concentration will be within the range of the reported value ±MU. This value is based on analytical variability (precision) and does not reflect other factors such as sample collection and handling which may also affect the result.
Example
Reported sodium = 140 mmol/L
Sodium MU = 1%
Expanded uncertainty = 140 mmol/L ± 1% or 140mmol/L ± 1.4 mmol/L
Interpretation - the true value of sodium in the sample is in the range 138.6-141.4 mmol/L, with 95% confidence.
Measurement Uncertainty
Who can order this test?
Currently, this test is only orderable by physicians outside of the province of British Columbia.
Following current clinical guidelines, testing is recommended only for patients with objective cognitive impairment (i.e., MCI or mild dementia) presenting for care at a specialized memory clinic.
Are special collection kits required?
No. Standard EDTA collection tubes are used.
Are their special collection and processing steps required to ensure test accuracy?
No. Phosphorylated tau 217 is not affected by routine collection and processing proceedures and can be processed following standard clinical laboratory protocols.
Interpretive guidance
Medical decision limits
Medical decision limits were determined using a two cut-point model, in which lower and upper thresholds were selected to achieve ≥90% sensitivity and ≥90% specificity for the presence of Alzheimer’s disease pathology as determined by comparison to CSF Alzheimer’s disease core biomarkers.
Medical decision limits and their performance characteristics apply only to populations with a high prevalence of Alzheimer’s disease, such as specialized memory clinics. In lower prevalence populations the medical decision limits (and related performance characteristics) are not applicable.
Table. Medical decision limits and performance characteristics.
Medical decision limit (MDL) | Interpretation | Explanation |
< Lower MDL | Negative | Rule-out AD pathology for concentrations below the lower MDL (90% sensitivity for detection of AD pathology above the lower MDL) |
Lower - upper MDL | Intermediate | Consider confirmatory testing by CSF for AD core biomarkers or amyloid PET for concentrations between the two MDLs |
> Upper MDL | Positive | Rule-in AD pathology for concentrations above the upper MDL (90% specificity for detection of AD pathology) |
Comorbidities
The performance of ptau217 in plasma has not been extensively characterized in the presence of other comorbidities. Research studies have demonstrated an association of eGFR with plasma ptau217, with eGFR <60 associated with increased plasma ptau217 compared to individuals with eGFR ≥60. Mean increases observed in plasma ptau217 were modest (12-15%). As is the case with most protein biomarkers measured in blood, there is no corrective calculation available to apply to ptau217 by degree of kidney dysfunction.
Resources specific to out-of-province (non-BC) practitioners
Invoicing information - For out-of-province requisitions, financial information for the ordering physician must be on-file with the lab before testing will be performed.
Resources for researchers
Our laboratory is experienced in supporting a wide range of research studies from translational research studies to multi-site/multi-national clinical trials. Our laboratory is accredited by the College of Physicians and Surgeons of British Columbia Diagnostic Accreditation Program. Please see our Research page for additional details.