CSF total protein

Definition
CSF total protein is a test to determine the amount of protein in cerebrospinal fluid (CSF). CSF is a clear fluid that circulates in the space surrounding the spinal cord. An abnormal protein level in the CSF suggests that there is an abnormal process occurring in the central nervous system.

How the test is performed
A sample of CSF is obtained, usually by lumbar puncture (spinal tap). The cerebrospinal fluid is then analyzed in the lab.

How the test will feel

Patients will be asked to either sit up or lie down on their sides with the back parallel to the bed and the chin tucked under and the legs curled in the fetal position. The healthcare provider will use the bony protrusions of the hip to determine the most appropriate location to remove fluid. This is usually at what is known as the L3-L4 vertebral level.

Subsequently iodine will be used to clean off the area and a sterile sheet will be draped over the surrounding area. In infants and small children, EMLA cream, a local anesthetic cream will be used to numb the skin and will be applied about 1 hour prior to the procedure. In adults, lidocaine will be injected under the skin initially, and then deeper such that tissue beneath the skin will also be numbed.

A thin 20-gauge needle will then be inserted into the interspace between the vertebra. Depending on how much subcutaneous tissue there is, this may require shallow or deeper penetration of the needle. There may be an audible “pop” when the needle penetrates the dura (membrane that surrounds the spinal cord and encases the fluid). At that point there will be fluid flowing out of the needle and this will be collected in plastic containers. Under normal circumstances, the opening pressure will be measured with a manometer and then about 20-30 cc of spinal fluid will be collected and sent for evaluation under the microscope.

Under experienced hands there should not be any pain. There may be a feeling of pressure when the needle is inserted but with appropriate anesthetic, this should not hurt. Occasionally, some people may feel numbness shooting down the leg. This may be due to irritation of a nerve root.

The needle is withdrawn, the sensation subsides and is not permanent. Following the procedure, the patient is advised to remain lying down for an hour or two to prevent low-pressure headaches. The entire procedure takes approximately 20 minutes.

Why the test is performed
The CSF total protein count may be helpful in diagnosing tumors, infection polyneuritis (inflammation of several groups of nerve cells), vasculitis, blood in the CSF, and trauma.

Normal Values
The normal protein range is 15 to 45 mg/dl.

Note: mg/dl = milligrams per deciliter

What abnormal results mean
When the protein level increases considerably, it may indicate the presence of tumors, hemorrhage, polyneuritis, trauma, or blood in the CSF.

When the protein level decreases, it can indicate rapid CSF production.

Additional conditions under which the test may be performed:

     
  • chronic inflammatory polyneuropathy  
  • primary lymphoma of the brain  
  • hemorrhage - intracerebral (deep)  
  • hemorrhage - intracerebral (hypertensive)  
  • hemorrhage - intracerebral (lobar)  
  • hemorrhage - intracerebral  
  • hemorrhage - subarachnoid

CSF protein levels must be interpreted in the context of clinical findings and results of other laboratory tests before a diagnosis can be made.

What the risks are

     
  • Risks of lumbar puncture include:       o hypersensitivity (allergic) reaction to the anesthetic       o discomfort during the test       o headache after the test       o bleeding into the spinal canal       o infection  
  • Brain herniation (if performed on a person with increased intracranial pressure), and resulting in brain damage and/or death. This test is not performed on anyone with clinical signs or imaging suggestive of increased intracranial pressure.  
  • Transient leg numbness or tingling due to irritation of a nerve root by the needle.

Johns Hopkins patient information

Last revised: December 4, 2012
by Amalia K. Gagarina, M.S., R.D.

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