Cerebrospinal Fluid

Medically Reviewed by Poonam Sachdev on April 15, 2024
4 min read

Cerebrospinal fluid is the liquid around your brain and spinal cord. If a doctor thinks you have an illness that affects your nervous system, they might take a sample for testing.

The fluid is made by a group of cells, called the choroid plexus, that are deep inside your brain. Your body has about 150 milliliters of fluid – roughly two-thirds of a cup.

As the colorless fluid goes around your brain and spinal cord, it cushions those organs, picks up needed supplies from your blood, and gets rid of waste products from brain cells.

Sometimes, cerebrospinal fluid can have things in it that shouldn't be there, like bacteria or viruses that can attack your brain. With some illnesses, what's in that fluid can help your doctor figure out what's going on.

Cerebrospinal fluid is made up of water, sugars, proteins, lipids, and electrolytes.

It has a lot of the same components as plasma, which is the liquid part of your blood. But cerebrospinal fluid contains much lower amounts of protein than plasma does.

The choroid plexus is a network of blood vessels in the innermost part of the brain. It produces cerebrospinal fluid in your brain’s ventricles (fluid-filled spaces). Special cells that line the ventricles also make a smaller amount of cerebrospinal fluid.

A sample of cerebrospinal fluid can be an important clue. It can tell your doctor if you have one of a number of conditions, such as:

  • Multiple sclerosis (when your body's immune system attacks your nerves) or similar conditions known as autoimmune diseases
  • Myelitis: Inflammation of your spinal cord
  • Encephalitis: Inflammation of your brain cells
  • Meningitis: Inflammation of the thin tissues that cover and protect your brain and spinal cord. This usually is caused by an infection in the cerebrospinal fluid.
  • A stroke or similar condition that causes bleeding around your brain
  • Leukemia: A kind of blood cancer
  • Dementia


Your doctor will use a procedure called a spinal tap or lumbar puncture. They'll take a sample of cerebrospinal fluid with a long, thin needle. You'll get a local anesthetic to numb the skin in the area, and the needle will go in between two of your vertebrae, the bones that surround your spinal cord and make up your spine. They'll take a tablespoon or two of the fluid for testing.

It usually takes about 45 minutes. You'll rest for a while afterward and may be told not to do anything strenuous for about a day. You may have a headache afterward, but tell your doctor if it lasts more than a few hours.

Lumbar puncture risks

A lumbar puncture usually doesn’t cause many risks. Doctors consider it a safe procedure.

In rare cases, you could have problems, like:

  • Infection
  • Lingering back pain
  • Nerve damage
  • Hearing loss
  • Double vision
  • Blood clots

What's in your cerebrospinal fluid can help your doctor identify or rule out various diseases.

  • If you have high levels of a substance called immunoglobulin, which your body uses to fight disease, or other things related to your nerve cells, that could point to multiple sclerosis or another autoimmune disorder, like Guillain-Barré syndrome.
  • If your doctor thinks you have Alzheimer's disease or another kind of dementia, certain types of proteins linked to the disease may be in the fluid.
  • Discolored fluid might be a sign of a cerebral hemorrhage (bleeding in your brain) or stroke.
  • Signs of bacterial or viral infection could tell your doctor you have an illness like meningitis or encephalitis.
  • Your doctor may be able to tell if you have other diseases, like certain cancers, neurosyphilis (an infection that affects the brain or spinal cord), Reye's syndrome (a disease that causes problems with the brain and other organs), or normal pressure hydrocephalus (a rare condition that’s caused by a buildup of cerebrospinal fluid). 


Cerebrospinal fluid is an important liquid that cleans out impurities in your brain, delivers nutrients, and provides cushion for your brain and spinal cord. You may need a spinal tap to remove a little cerebrospinal fluid. This can tell your doctor if you have certain medical conditions. 

What are the symptoms of a spinal fluid leak?

A spinal fluid leak happens when cerebrospinal fluid leaks through a tear or hole in the tissue that surrounds your brain. Some symptoms of a spinal fluid leak are a headache, meningitis, ringing in your ears, cerebrospinal fluid that leaks from your nose, or vision problems. 

What happens if you run out of cerebrospinal fluid?

If you have a cerebrospinal fluid leak, you will have less fluid to support and cushion your brain. You might not notice this if the leak is small. If the leak is big, your brain can drop in your skull. This can affect how parts of your brain work.

How long does it take for cerebrospinal fluid to replenish?

Everyone is different. Generally, your body can replace its supply of cerebrospinal fluid about every 7.5 hours.