Elecsys® Phospho-Tau (181P) CSF

Robust and accurate biomarker tests to aid clinical decisions

Elecsys® Phospho-Tau (181P) CSF
Robust and accurate biomarker tests to address unmet needs in Alzheimer’s disease

Elecsys® Phospho-Tau (181P) CSF is an in vitro diagnostic immunoassay intended for the quantitative determination of the pTau 181 (Tau protein phosphorylated at threonine 181) concentration in human cerebrospinal fluid (CSF). Paired with the Elecsys® β-Amyloid (1-42) CSF II assay, the pTau181/Abeta42 ratio measures two main biomarkers of Alzheimer’s pathology, beta-amyloid 42 and phosphorylated tau 181 proteins, in adults ages 55 and older being evaluated for AD or other causes of cognitive impairment.1

The abnormal phosphorylation of tau protein leads to formation of intracellular neurofibrillary tangles. Together with the amyloid plaques, these modifications constitute the hallmark pathologies in AD and changes in these biomarkers were shown to occur before clinical symptoms.2,3 Studies demonstrated that while Abeta42 levels in CSF decrease to around half the level in controls, CSF pTau181 levels increase around 2‑3 fold in mild‑moderate AD patients compared to age‑matched controls.4,5

Biomarker confirmation of amyloid positivity either by amyloid PET or CSF testing is one of the requirements listed in the appropriate use recommendations for amyloid-targeting therapies.6

The Elecsys® pTau181 CSF assay is not intended to be used as a stand-alone test and should only be used with the Elecsys® β-Amyloid (1-42) CSF assay to calculate the ratio of Phospho-Tau (181P) (pTau181) to β-Amyloid (1-42) (Abeta42) in CSF (pTau181/Abeta42 ratio).1

A negative result, defined as pTau181/Abeta42 ratio value below cutoff or an Abeta42 value above the measuring range, is consistent with a negative amyloid positron emission tomography (PET) scan result and reduces the likelihood that a patient’s cognitive impairment is due to AD. A positive result, defined as pTau181/Abeta42 ratio value above cut‑off, is consistent with a positive amyloid PET scan result.1

Although a positive result does not establish a diagnosis of AD or other cognitive disorder, the use of the pTau181/Abeta42 ratio result in addition to other clinical diagnostic evaluations enhances diagnosis accuracy and can streamline patient management.1,7,8


Don't wait to confirm amyloid positivity and unlock new therapies for more patients.

Contact us


  1. Elecsys Phospho-Tau (181P) CSF 2022-12.
  2. Busche, M.A., Hyman, B.T. Synergy between amyloid-β and tau in Alzheimer’s disease. Nat Neurosci 23, 1183–1193 (2020).
  3. Alzheimer’s Association. 2023 Alzheimer’s Disease Facts and Figures. Alzheimers Dement 2023;19(4).
  4. Mattsson N, Zetterberg H, Hansson O, et al. CSF biomarkers and incipient Alzheimer disease in patients with mild cognitive impairment. JAMA. 2009;302(4):385-393.
  5. Hampel H, Blennow K. CSF tau and β-amyloid as biomarkers for mild cognitive impairment. Dialogues Clin Neurosci. 2004;6(4):379-390.
  6. Cummings, J., Apostolova, L., Rabinovici, G.D. et al. Lecanemab: Appropriate Use Recommendations. J Prev Alzheimers Dis (2023).
  7. Sabbagh MN, Lue LF, Fayard D, Shi J. Increasing Precision of Clinical Diagnosis of Alzheimer's Disease Using a Combined Algorithm Incorporating Clinical and Novel Biomarker Data. Neurol Ther. 2017;6(Suppl 1):83-95.
  8. Hansson, O. et al. (2018). CSF biomarkers of Alzheimer’s disease concord with amyloid-β PET and predict clinical progression: A study of fully automated immunoassays in BioFINDER and ADNI cohorts. Alzheimers Dement 14(11), 1470-1481.

Elecsys® Phospho-Tau (181P) CSF test characteristics

  • Testing time

    18 minutes

  • Test principle

    Two-step sandwich 

  • Calibration


  • Sample material

    Cerebrospinal Fluid (CSF)

  • Sample volume

    30 µL - cobas e 801 module and cobas e 402 module 

    50 µL - cobas e 411 analyzer and cobas e 601/602 modules

  • LoB (Limit of Blank)

    4 pg/mL

  • LoD (Limit of Detection)

    8 pg/mL

  • LoQ (Limit of Quantitation)

    8.0 pg/mL


  • Measuring range

    8.0 – 120 pg/mL


  • Reagent onboard-stability

    16 weeks - cobas e 801 module and cobas e 402 module

    28 days - cobas e 411 analyzer and cobas e 601/602 modules