Tau Protein
Note: this site is for informational purposes only. To view test results or book a test, use the NHS app in England or contact your GP.
A tau protein test measures the level of tau protein in the cerebrospinal fluid using a sample collected by lumbar puncture (spinal tap). It is used to help evaluate and support the diagnosis of conditions affecting the brain, particularly Alzheimer’s disease and other forms of dementia.
Why get tested?
To help identify cerebrospinal fluid (CSF) fluid leaking from the skull.
When to get tested?
If there is a watery discharge from your nose or ear (rhinorrhoea or otorrhoea) after you have suffered a skull fracture or after brain surgery.
Sample required?
A sample of the suspicious watery discharge is collected into a plastic tube and at the same time a blood sample is also collected.
Test preparation needed?
None
Common questions
If you suffer an injury (e.g. skull fracture) which causes a tear in the membranes covering the brain and spine, CSF may leak out from your nose or ear (rhinorrhoea or otorrhoea). It may be necessary to distinguish CSF from other watery discharge in these circumstances. This involves looking for the presence of something which would normally only be found in CSF, such as tau protein. This is a form of transferrin present in CSF but not usually found in blood, nasal secretions, or other body fluids. The suspected CSF should be examined along with a serum sample to confirm results.
Tau protein would be requested when there is doubt over the origins of watery ear or nose discharge, following a high risk event such as a head injury.
If the fluid from the nose or ear is indeed CSF, tau protein would be detected when the fluid sample was analysed. However, tau protein may be found in blood in certain circumstances, e.g. when the individual naturally produces certain transferrin types due to genetic variation, or when an individual consumes large amounts of alcohol. This is why a blood sample must be examined at the same time as the suspected CSF.
CSF leaking from the nose or ear is very rare. Most nasal and ear discharges have an obvious straightforward explanation e.g. infection, and this type of analysis is only required in a very small number of cases where a doctor has a high level of suspicion about the source of discharge.
Tau protein is present in the neurofibrillary tangles found in Alzheimer disease. There is therefore interest in whether measurement of tau protein may help with diagnosis and monitoring of Alzheimer disease. Research is ongoing. Measurement in dementia is not recommended in routine clinical practice currently.