CSF protein is largely an ultrafiltrate of plasma, and is predominantly made up of low molecular weight and medium molecular weight proteins. In normal health, the protein concentration of CSF is approximately 100-fold less than that of plasma.
There are many causes of an elevated CSF protein. Therefore this test is a non-specific biomarker of CNS pathology that may be of some diagnostic use when applied to the relevant clinical context.
Heavily blood stained specimens and specimens containing clots are unsuitable for analysis
Elevations of CSF protein may occur for a number of reasons. The table below is adapted from Tietz Textbook of Clinical Chemistry and Molecular Diagnostics, 6th Edition (Rifai, Horvath & Wittwer) and is a non-exhaustive list of some of the more common causes of a high CSF protein. The result should be interpreted in the clinical context which will allow for a narrowing of the differential diagnosis.
|Increase in permeability of blood-brain barrier||Meningitis (bacterial, viral, fungal), encephalitis, CNS neoplasms|
|Intrathecal production of protein (usually immunoglobulin)||Multiple sclerosis and other demyelinating conditions (e.g. Guillain-Barre syndrome).|
|Cerebral haemorrhage||Sub-arachnoid haemorrhage, subdural haematoma, intracerebral haemorrhage|
|Mechanical obstruction of CNS flow||Spinal cord tumour or abscess|
|Specimen contamination||Traumatic tap|
A common cause of a high CSF protein is contamination with venous blood due to a traumatic collection (bloody tap). CSF protein can be markedly elevated depending upon the degree of contamination. CSF protein results usually should not be interpreted in blood-stained specimens.
0.15 – 0.40 g/L
This reference interval applies to adult patients where the CSF is collected from a lumbar puncture. The CSF protein concentration tends to be higher in neonates, and is lower in CSF specimens collected from the ventricular system.
Spectrophotometry (pyrogallol red) on a Beckman Coulter AU5822 analyser.
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