26850 Phospho-Tau 217, Plasma (PT217)

​Centrifuge and aliquot plasma into plastic vial. 

Do not submit in original tube.

Gross Hemolysis

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.

The two main neuropathologic features observed in the brain of patients with Alzheimer disease (AD) are the presence of plaques composed of beta-amyloid (Abeta) peptides and intracellular neurofibrillary tangles containing hyperphosphorylated Tau (p-Tau) proteins. To date, positron emission tomography (PET) and cerebrospinal fluid (CSF) biomarkers are the most widely used biomarkers in clinical practice for detection of Abeta and tau pathologies. There are several PET tracers that can detect the load of Abeta fibrils in the brain (amyloid-PET). Studies have demonstrated high concordance between the in vivo uptake of these amyloid-PET tracers and the density of Abeta plaques as determined post-mortem. In CSF, Abeta42 concentrations and especially the ratios of Abeta42/Abeta40 and p-Tau181/Abeta42 concentrations correlate strongly with amyloid-PET status and AD neuropathology. Several CSF Abeta and p-Tau assays on high-performing, fully automated platforms are currently used in clinical practice. However, there is a need for accurate AD blood-based biomarkers that are easily accessible and minimally invasive.

Different p-Tau isoforms that are increased in the presence of amyloid pathology are detectable in plasma, including pTau181, pTau217, and pTau231. Head-to-head comparisons of assays for p-Tau181, p-Tau217, and p-Tau231 using plasma from patients with mild cognitive impairment indicate that increases in plasma p-Tau217 were superior at detecting AD pathology and predicting future development of AD dementia. Both p-Tau181 and p-Tau217 were associated with both Abeta plaques and tau tangles, with p-Tau217 showing stronger correlations with both pathologies. In addition, plasma concentrations of p-Tau217, but not p-Tau181 and p-Tau231, have been shown to increase over time in people with abnormal brain Abeta deposition correlating with brain atrophy and cognitive decline.

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-PET and a Centiloid scale value of 25 or more. 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.