Tau protein

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.

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.