Phospho-Tau 217, Plasma (Sendout)

Useful For: Evaluation of individuals, aged 50 years and older, presenting with cognitive impairment who are being assessed for Alzheimer disease and other causes of cognitive decline.

Ordering Guidance:

• This assay should not be ordered for individuals younger than 50 years or in cognitively unimpaired individuals regardless of age.
• This test is not intended as a screening test for Alzheimer disease in asymptomatic individuals.

Ordering Requirements: Pre-approved for the UW Medicine Memory & Brain Wellness Center. Orders from other locations require Laboratory Medicine Resident (LMR) approval.

Reference Values:

Interpretation:

Negative: A normal (negative) phosphorylated Tau217 (p-Tau217) result is consistent with a negative (normal) amyloid positron emission tomography (PET) scan result. This result indicates a reduced likelihood that an individual has neuropathological changes associated with Alzheimer disease.

Intermediate: An intermediate p-Tau217 result cannot accurately differentiate between the presence or absence of neuropathological changes associated with Alzheimer disease. Further testing, such as amyloid positron emission tomography (PET) or cerebrospinal fluid Abeta42 and tau biomarkers, is needed to determine the likelihood of neuropathological changes associated with Alzheimer disease being present.

Positive: An elevated (positive) p-Tau217 result is consistent with a positive (abnormal) amyloid positron emission tomography (PET) scan result. This result is consistent with the presence of neuropathological changes associated with Alzheimer disease. In the proper clinical context this test is supportive of Alzheimer disease being related to current clinical symptoms. This test has not been demonstrated to provide information on the risk of an asymptomatic individual developing symptoms related to Alzheimer disease in the future.

Clinical performance of this test was established in a study of 427 individuals aged 50 years and older with mild cognitive impairment or early dementia with a 64% prevalence of amyloid pathology defined by an amyloid-positron emission tomography (PET) and a Centiloid of > or =25. For detection of an abnormal amyloid-PET, pTau217 test sensitivity at the lower cutpoint (< or =0.185 pg/mL) was 92% and the specificity at the upper cutpoint (> or =0.325 pg/mL) was 96%. The diagnostic performance of this test has not been established in asymptomatic individuals.¹

Cautions:

Phosphorylated Tau217 (p-Tau217) results must be interpreted in conjunction with other diagnostic tools, such as neurological examination, neurobehavioral tests, imaging, and routine laboratory tests.

This assay should not be ordered for individuals younger than 50 years.

Elevations of p-Tau217 may be seen in individuals with impaired kidney function associated with chronic kidney disease and should be interpreted with caution in these situations.

False-positive or false-negative test results may occur.

The performance of this test was evaluated using specimens obtained from a US White population. At this time, it is uncertain if similar clinical performance will be observed in other racial and ethnic groups.

This assay should not be used for cognitively unimpaired (asymptomatic) individuals to predict the development of dementia or other neurological conditions.

The safety and effectiveness of this test have not been established for monitoring the effect of disease monitoring therapies or for predicting development of dementia or other neurologic conditions.

p-Tau217 concentrations have not been established to correlate with disease severity.

Results obtained with different assay methods or kits may be different and cannot be used interchangeably.

In rare cases, some individuals can develop antibodies to mouse or other animal antibodies (often referred to as human anti-mouse antibodies or heterophile antibodies) that may cause interference in some immunoassays. Caution should be used in interpretation of results, and the laboratory should be alerted if the result does not correlate with the clinical presentation.

Outside Laboratories: Centrifuge sample and transfer plasma to a separate plastic screw-top vial. Refrigerate plasma while awaiting shipment. Transport with a cold pack.

Stability: Refrigerated (preferred): 7 days; Frozen: 7 days; Ambient: 72 hours.

Centrifuge sample and transfer plasma into two separate aliquots. If sample volume is low, prioritize the sendout test (RPT217).

• RPT217: Aliquot 0.6 mL plasma into a screw-cap vial and place sample in the Refrigerated Mayo Sendouts Rack.
• UW443: Aliquot 0.5 mL plasma into a separate plastic vial and place sample in the -70°C UCGEN/Chemistry rack.
  • For samples collected at other locations: freeze samples prior to transport and send to UW-MT with the next Cross Hospital batch.

Sendouts:

• Order Mayo Test: PT217
• Interfaced: Yes [Interface: 601; Worksheet: MARF]

Stability: Refrigerated (preferred): 7 days; Frozen: 7 days; Ambient: 72 hours.