Test Overview
Clinical Utility
This test is intended to help rule in or rule out the presence of amyloid pathology that is consistent with Alzheimer’s disease (AD) but is not diagnostic on its own. Clinical correlation is required.
Plasma pTau217 concentration has been reported to have excellent discriminative ability for amyloid pathology when performed in cohorts of older adults with objective cognitive impairment concerning for AD; at the individual patient level, however, correlation with the clinical history and other ancillary test data are required when interpreting the plasma pTau217 concentration to ensure accurate diagnosis.
The diagnostic utility of this test in other cohorts, including younger patients (e.g. <50 years of age) or cognitively unimpaired patients, is not well-established; the test is not recommended for such patients at this time. For patients with values near the cut-offs, clinical correlation is particularly important.
Please note that impaired kidney function has been associated with elevation in plasma pTau217 concentration, so cautious interpretation is recommended in patients with impaired kidney function. Unusually high plasma pTau217 concentrations have also rarely been reported to represent a false elevation due to heterophilic antibody interference in patients with heterophilic antibodies.
A clinical diagnosis of AD in a patient with an abnormally elevated plasma pTau217 concentration should only be made after it has been determined that the patient presentation is compatible with AD and alternative diagnoses have been reasonably excluded.
Method
Electrochemiluminescent immunoassay (ECLIA)
Analytical Platform
Roche Elecsys
Method Description
This is a laboratory-developed test that is performed in an accredited laboratory. It is not Health Canada-approved but has received CE mark and is offered by LHSC for clinical use following internal validation.
Result Included
Phosphorylated Tau 217 (pTau217)
Specimen
Specimen Type
Plasma
Important Note: TEST ID: ALZP P
Non-interfaced clients should specify ICL TEST ID: ALZP P when ordering this test. Not doing so will cause processing delays while ICL ascertains which test you are requesting.
Similar testing is available for clinical use by a different method performed in Canada outside of Ontario: pTau217 by SiMoa, Plasma
Containers
Collection Containers
Lavender top (EDTA)
Volume
Sample Volume
2.0 mL
Minimum Volume
0.5 mL
Specimen Comment
Red, Gold or Light Green (Lithium Heparin) top tubes are NOT acceptable.
Collection & Handling
Handling Information
Spin promptly and aliquot plasma. Do not submit whole blood. Store and ship plasma frozen.
Stability
| Ambient | Refrigerated | Frozen |
|---|---|---|
| 2 days | 7 days | 60 days |
Rejection Criteria
| Criteria | Specification |
|---|---|
| Hemolysis | Gross |
Performance & Interpretation
Turnaround Time
8 days
Results
-
Phosphorylated Tau 217 (pTau217)pg/mLNormal: ≤0.223
Intermediate: 0.224-0.378
Abnormal: >0.378
Comment
A normal plasma concentration of pTau217 (≤0.223 pg/mL) is not consistent with Alzheimer’s disease (AD)-related pathologic change but cannot rule out a diagnosis of AD on its own. Clinical correlation is required.
A plasma concentration of pTau217 in the intermediate zone (0.224-0.378 pg/mL) is indeterminate for the presence of AD-related pathologic change. Clinical correlation is required.
An abnormally elevated plasma concentration of pTau217 (>0.378 pg/mL) is consistent with AD-related pathologic change but is not diagnostic of AD on its own. Clinical correlation is required.
Referral Location
Canada
Interface & Setup
HL7 Interface Codes
| Order Code | Result Name | Result Codes | Units |
|---|---|---|---|
| ALZP P | Phosphorylated Tau 217 (pTau217), Plasma | 66329 | pg/mL |
| pTau217 Result Classification, Plasma | 66330 | ||
| Alzheimer Interp (pTau217), Plasma | 66331 | ||
| General Alzheimer's Comment, Plasma | 66332 |
Test Version
Last Updated
2026-06-15