Alzheimer’s disease (AD) is a neurodegenerative disorder hallmarked by extracellular amyloid-beta (AB) plaques and intracellular neurofibrillary tangles of hyperphosphorylated tau (p-tau), which lead to progressive loss of neuronal function and cell death. These pathologies can be present and developing in the brain for years before any symptoms become apparent. During this buildup there are several specific proteins that are released into the cerebrospinal fluid (CSF) that have been identified as reliable biomarkers for the diagnosis of AD.

Tau protein normally acts to stabilize the axons of neurons, but when it is hyperphosphorylated (p-tau) it becomes prone to aggregating into neurofibrillary tangles, leading to neuronal dysfunction and death, There are several variants of p-tau that have been identified as significant in AD, differentiated by the location of the phosphorylation site.

The two most notable isoforms are p-Tau 181 and p-Tau 217. Levels of p-Tau 181 and 217 in both CSF and blood have been shown to be elevated in AD and increase over the course of the disease, indicating they could be a valuable tool for diagnosis, but the relative performance of the two has been an area of intense interest.

Elevated levels of p-Tau181 are associated with Aβ and tau pathologies in the brain and can be used to discriminate AD from non-AD dementias.

Test code:


Abbreviations, alternative names:

Plasma p-Tau181


In-house single-molecule array (Simoa)


Research use only (RUO)


Specimen type:

EDTA plasma

Minimum volume:

0.5 mL

Preferred volume:

5 mL

Rejection criteria:

Grossly hemolytic, lipemic, or icteric. If the sample arrives at room temperature

Our offices are only able to receive samples Mon-Fri, so samples must be shipped Mon-Thur. Samples arriving over the weekend may need to be re-drawn.


Specimen collection:

No patient preparation required before testing
Draw blood in K2 EDTA tubes (lavender top).
Invert 8 times to ensure complete mixing

Specimen handling:

Centrifuge EDTA tubes at 1800 - 2200 x g for 10-15 minutes
Draw off plasma into Aliquot tubes with pipette, ensuring not to take gel or RBC (middle/bottom layers)
Store Aliquot tubes in refrigerator (2°C - 8°C) until shipping

Specimen storage:

Plasma samples must either be refrigerated and shipped chilled within 24 hours of collection, or frozen and shipped on dry ice


Testing frequency:

On demand

Turnaround time:

3-10 business days

Reference range:

46.0 ng/L


Research use only (RUO)

Additional Information

  • Test results are for research use only. Not to be used for diagnostic purposes.

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