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What Is a Cerebral Spinal Fluid (CSF) Test? 
CSF is the watery fluid present around the brain and spinal cord. It functions as a protective shock absorber around these delicate organs, carries glucose, oxygen and ions and chemicals to the brain cells, and helps maintain the pH of blood. CSF also aids in the transportation of hormones, ions, proteins, enzymes from the brain and spinal cord.
A CSF test involves analysis of the levels of different chemicals and cells in the cerebral spinal fluid for the diagnosis of various diseases. The CSF for testing is extracted from the patient through a procedure called lumbar puncture (LP) or spinal paracentesis. An LP is done in the area of the lower back. If needed, it can sometimes also be taken from other parts around the brain and spinal cord.
A CSF test has now become an important part of the diagnosis of various conditions because it can help them decide further tests to be performed.The test is sometimes referred to as spinal tap, CSF culture, ventricular puncture or cisternal puncture.

  1. Why is a CSF test performed?
  2. How do you prepare for a CSF test?
  3. How is a CSF test performed?
  4. What do CSF test results indicate?

CSF test is mainly done to microscopically look for the presence of any infections or abnormal cells or to analyse proteins and chemicals in the body. A change in the levels of any substance could indicate an underlying condition. Therefore, a doctor may recommend a CSF test in the following cases:

The physical appearance and pressure while collecting the sample can also be an indication of certain disorders.

A CSF test can identify specific bacteria, viruses, brain-specific proteins and markers for inflammation and cancers. Thus, the doctor could perform a CSF test as a part of diagnosis for any of the following underlying conditions:

This test does not require special preparations. Make sure you are well-rested before the test and available for an entire day for the procedure, as proper rest is essential after the procedure. Also, it is important that you inform your doctor about any previous medical conditions you may have had or if you are taking any medicines or herbal supplements.

At the test centre, your doctor will first explain the basic procedure to you. The following steps will then be followed for the test:

  • You will be asked to lie down on the bed on one side and curl up in a foetal position with your legs close to your chest
  • Your doctor will clean the area of puncture, ie on the lower back between two bones (vertebrae), to make it sterile and he/she will apply a numbing cream
  • A sterilised needle will then be slowly inserted between two bones to collect the fluid 
  • The doctor will use a manometer to check the pressure of the fluid at this point
  • Once the fluid is withdrawn, the needle will be slowly removed 
  • The area will be covered with a cotton gauze and bandage
  • You will be asked to remain in the foetal position for some time and take rest for a few hours

A slight tingling sensation may be felt due to the numbing cream applied on the lower back. You might also have a headache after the procedure, which may last several hours. Inform the doctor if the headache prolongs.

If you feel nauseated, your doctor may advise you to stay on intravenous fluids. In extremely rare cases, there could be a chance of infection due to the procedure. The doctor will recommend antibiotics accordingly.
​It is essential that you remain calm throughout the test. Lying in the foetal position for long may be uncomfortable, but if you do not move, the procedure will be completed in approximately 30 minutes.

Normal results: The following values would indicate normal results:

Pressure

8-20 centimetres (cm) H2O

Appearance

Clear and colourless water-like

Protein

15-60 milligrams (mg)/100 millilitres (mL)

Glucose

50-80 mg/100 mL (or greater than 2/3 of blood sugar level taken simultaneously)

Glutamine

6-15 mg/decilitres (dL)

Lactate dehydrogenase

less than 2.0-7.2 units (U)/mL

White blood cells (WBCs)

0-4/ cubic millimetres (mm3)

Chloride

110-125 milliequivalents (mEq)/litre (L)

Abnormal results: Values outside the normal range are indicative of an underlying condition. The following table gives a detailed list of conditions that could be associated with abnormal results.
 

Pressure

Increased

Increased pressure in the skull

Decreased

Tumour in the spinal cord, diabetic coma

Appearance

Cloudy

Presence of infections, WBCs or proteins

Bloody

Bleeding or obstruction in the spinal cord

Brown, yellow, orange

Signs of previous bleeding

Protein

Increased

Breakdown of the blood-brain barrier and infections due to bacteria, virus or fungus

Decreased

Excess CSF production

Glucose

Decreased 

Bacterial infection or fungal infection leading to meningitis, tuberculosis

Increased

High blood sugar

WBCs

Increased

Bacterial and viral infections, tumours, multiple sclerosis, stroke or abscess

  • Presence of specific strains of bacteria and virus could be indicative of the specific disease
  • Presence of cancerous cells is similarly an indication of the specific type of cancer
  • Presence of red blood cells is an indication of a traumatic LP process
  • Presence of antibodies could be an indication of diseases like Guillain-Barre syndrome, multiple sclerosis or even neurosyphilis
  • Other diseases that could also be indicated by the CSF test are encephalitis, Alzheimer’s, hepatic encephalopathy, Reye syndrome and amyotrophic lateral sclerosis (ALS).

Disclaimer: All results must be clinically correlated with the patient’s complaints to make a complete and accurate diagnosis. The above information is provided from a purely educational point of view and is in no way a substitute for medical advice by a qualified doctor.  

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References

  1. Gerard J. Tortora, Bryan Derrickson. Cerebrospinal fluid 14th ed. U.S: Wiley Publication; 2014. Chapter 14, pp 477-478
  2. American Family Physician. [Internet] . American Academy of Family Physicians. U.S Cerebrospinal fluid
  3. Nicklaus Children Hospital. [Internet]. U.S Cerebral spinal fluid (CSF) collection
  4. Jurado R, Walker HK. Clinical Methods: The History, Physical, and Laboratory Examinations 3rd edition. Boston: Butterworths; 1990. Chapter 74
  5. William J. Marshall, S. K. Bangert. Clinical Biochemistry: Metabolic and Clinical Aspects 3rd Edition London : Elsevier Publishing 2014, Page no: 660-672
  6. UCSF health: University of California [internet]; CSF Chemistry
  7. Provan D.Oxford Handbook of Clinical and Laboratory Investigation 4th ed. United Kingdom: Oxford University Press; 2018. Page no: 418.