Elecsys® Total-Tau CSF (tTau) is an in vitro diagnostic immunoassay intended for the quantitative determination of the total tau (the 6 human brain Tau isoforms) protein concentration in human cerebrospinal fluid (CSF). Paired with the Elecsys® β-Amyloid (1-42) CSF assay, the tTau/Abeta42 ratio measures two biomarkers of Alzheimer’s pathology, beta-amyloid 42 and tau proteins, in adults ages 55 and older being evaluated for AD or other causes of cognitive impairment.1
Studies have shown that while CSF β‑Amyloid (1‑42) levels decrease to around half the level in controls, CSF tTau levels increase around 2‑3 fold in mild-moderate AD patients compared to age‑matched controls.2,3
The Elecsys® Total-Tau 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 Total-Tau (tTau) to β-Amyloid (1-42) (Abeta42) in CSF (tTau/Abeta42 ratio).1
A negative result, defined as tTau/Abeta42 ratio value below cutoff 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 tTau/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 disorders, the use of tTau/Abeta42 ratio in addition to other clinical diagnostic evaluations enhances diagnosis accuracy and can streamline patient management.1,4,5