To help identify cerebrospinal fluid (CSF) fluid leaking from the skull.
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.
A sample of the suspicious watery discharge is collected into a plastic tube and at the same time a blood sample is also collected.
Your healthcare practitioner will advise you of any preparatory requirements.
Cerebrospinal fluid (CSF) is normally found only within the brain and the spinal canal. If you suffer an injury which causes a tear in the membranes covering the brain and spine, CSF may leak out. This may sometimes cause watery fluid to drip from either the nose or the ear (rhinorrhoea or otorrhoea). Distinguishing CSF from other watery discharge involves looking for the presence of something which would normally only be found in CSF. Tau protein is beta 2 transferrin. This form of transferrin is present in CSF but not usually found in blood, nasal secretions, or other body fluids. The suspected sample should be examined along with a serum sample to confirm results.
How is the sample collected for testing?
The suspicious watery discharge will be collected into a plain plastic tube. A sample of blood will also be taken from a vein in your arm at the same time.
Is any test preparation needed to ensure the quality of the sample?
This is not a blood test but one that is performed on a sample of spinal fluid. Follow any preparatory instructions provided.
How is it used?
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. This may cause a watery discharge 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.
When is it requested?
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.
What does the test result mean?
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.
Is there anything else I should know?
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.