Cerebrospinal Fluid Examination
Basic Facts
Cerebrospinal fluid (CSF) examination is a laboratory test that analyzes the fluid surrounding the brain and spinal cord.
The fluid is usually extracted during a procedure called a lumbar puncture.
CSF examination helps physicians diagnose myriad conditions, including infection, brain tumors, spinal tumors.
Cerebrospinal fluid (CSF) examination is a laboratory test that analyzes the fluid surrounding the brain and spinal cord. Cerebrospinal fluid is a clear fluid that cushions the brain to protect it from injury and flushes toxins out of the brain. The fluid is usually extracted from the spinal cord during a procedure called a lumbar puncture (LP). The procedure is performed in the lower back, called the lumbar region.

Analyzing the CSF can help physicians diagnose the following conditions:
  • Infections;
  • Brain and spinal tumors;
  • Cancerous cells or tumors in the meninges (the membrane that surrounds the brain);
  • Dementia;
  • Multiple sclerosis;
  • Guillain-Barre syndrome;
  • Vasculitis; and
  • Subarachnoid hemorrhage.
When analyzing CSF, technicians evaluate the following characteristics and substances in the fluid for signs of a condition:
  • Clarity and color;
  • Bacterial cultures;
  • White blood cells;
  • Protein;
  • Glucose;
  • Chloride;
  • Lactic dehydrogenase; and
  • Cancerous cells.

No fasting is required prior to a lumbar puncture. The physician may instruct the patient to use the restroom prior to the procedure.

Prior to the test, the physician will often perform a neurologic assessment that tests the patient's legs for strength, sensation, and movement.


Patients with an infection near the insertion site or patients who have increased pressure in the brain can place patients at greater risk for complications following the procedure. The physician may recommend that these patients not have an LP performed.


The patient wears a hospital gown and lies on their side with their legs pulled up toward their chest. In some cases, patients may sit on an exam table and lean forward with their head resting on pillows in their lap.

After cleaning the area and giving the patient a local anesthetic, the physician inserts a needle between two vertebrae in the patient's lower back until it enters the spinal canal. When the needle is in place, the physician may take a pressure reading of the CSF and then withdraws the CSF, which is sent to the laboratory for analysis.


Patients are sometimes instructed to lie on their back for 6 to 12 hours. To help avoid a lumbar puncture headache, patients should minimize sitting or standing for long periods during the first 12 hours after the test. Patients are instructed to drink plenty of liquids to help replace the CSF.


Headache after a lumbar puncture is the most common post-procedure complication. Other side effects may include pain or an aching feeling in the patient's neck or low back, nausea, vomiting, or ringing in the ears.

Complications from a lumbar puncture are rare; however, a lumbar puncture can make the following conditions or symptoms worse:
  • Brain herniation;
  • Spinal cord compression;
  • Subarachnoid bleeding;
  • Double vision;
  • Back pain; and
  • Radicular symptoms.
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