Spinal tap (lumbar puncture)
A spinal tap (lumbar puncture) is a procedure in which a needle is inserted into the spinal canal to measure the pressure and obtain a sample of cerebrospinal fluid (CSF), the colorless fluid that surrounds the brain and spinal cord. The procedure may also be used to inject anesthetics, medicine, or a contrast dye (for spinal X-rays) into the spinal fluid. And it may be used to drain fluids that build up as a result of certain medical conditions.
Fluid samples obtained from a spinal tap can be analyzed for signs of infection (such as meningitis), inflammation, cancer, or bleeding in the area around the brain or spinal cord.
Why is a spinal tap (lumbar puncture) done?
A spinal tap is done to:
- Find a cause for symptoms possibly caused by an infection (such as meningitis), inflammation, cancer, or bleeding in the area around the brain or spinal cord (such as subarachnoid hemorrhage).
- Diagnose certain diseases of the brain and spinal cord, such as multiple sclerosis or Guillain-Barré syndrome.
- Measure the pressure of cerebrospinal fluid (CSF) in the space surrounding the spinal cord. If the pressure is high, it may be causing certain symptoms.
A spinal tap may also be done to:
- Put anesthetics or medicines into the CSF. Medicines may be injected to treat leukemia and other types of cancer of the central nervous system.
- Put a dye in the CSF that makes the spinal cord and fluid clearer on X-ray pictures (myelogram). This may be done to see if a disc or a cancer is bulging into the spinal canal.
In rare cases, a spinal tap may be used to lower the pressure in the brain caused by too much CSF.
How is a spinal tap (lumbar puncture) done?
A spinal tap may be done in your doctor's office, in an emergency room, or at your bedside in the hospital. It may also be done in the radiology department if fluoroscopy is used.
You will empty your bladder before the procedure.
The doctor also may look into your eyes using a special lighted scope (ophthalmoscope) to see if the pressure is high. If the pressure is high, you may need other tests before the spinal tap.
You will lie on a bed on your side with your knees pulled up toward your chest. Or you may sit on the edge of a chair or bed and lean forward over a table with your head and chest bent toward your knees. These positions help widen the spaces between the bones of the lower spine so that the needle can be inserted more easily. If fluoroscopy is used, you will lie on your stomach so the fluoroscopy machine can take pictures of your spine during the procedure.
Your doctor marks your lower back (lumbar area) with a pen where the puncture will occur. The area is cleaned with a special soap and draped with sterile towels. A numbing medicine (local anesthetic) is put in the skin.
Then a long, thin needle is put in the spinal canal. When the needle is in place, the solid central core of the needle (stylet) is removed. If the needle is in the right spot in the spinal canal, a small amount of cerebrospinal fluid (CSF) will drip from the end of the needle. If not, the stylet will be put back in and the needle will be moved in a little farther or at a different angle to get to the fluid. Your doctor may need to move to another area of your spine if it is hard to get to the spinal fluid.
When the needle is in the spinal canal, a device called a manometer is hooked to the needle to measure the pressure of the CSF. You may be asked to straighten your legs while you are lying down. Your doctor takes the pressure reading, called the opening pressure, and checks whether the fluid is clear, cloudy, or bloody. Several small samples of fluid are collected and sent to the lab for study.
A final pressure reading, called the closing pressure, may be taken after the fluid samples are done. The needle is taken out and the puncture site is cleaned and bandaged.
Following a spinal tap, you may be told to lie flat in bed or with your head slightly raised for 1 to 4 hours. Since your brain makes new CSF all the time and replaces it 2 or 3 times a day, the small amount of fluid that is removed will be quickly replaced.
How do you prepare for a spinal tap (lumbar puncture)?
- Tell your doctor ALL the medicines, vitamins, supplements, and herbal remedies you take. Some may increase the risk of problems during your test. Your doctor will tell you if you should stop taking any of them before the test and how soon to do it.
- If you take aspirin or some other blood thinner, ask your doctor if you should stop taking it before your test. Make sure that you understand exactly what your doctor wants you to do. These medicines increase the risk of bleeding.
- You will be asked to sign a consent form that says you understand the risks of the test and agree to have it done.
What do the results of a spinal tap (lumbar puncture) mean?
Many different tests can be done on the fluid (cerebrospinal fluid, or CSF) collected during a spinal tap. Some results will be ready right away, some will take a few hours after the procedure, and others will take several weeks.
Each lab has a different range for what's normal. Your lab report should show the range that your lab uses for each test. The normal range is just a guide. Your doctor will also look at your results based on your age, health, and other factors. A value that isn't in the normal range may still be normal for you.
Values may include CSF pressure, protein, glucose, and cell counts.
| Appearance: | CSF is normally clear and colorless. |
| Other results: | No infectious organisms (such as bacteria, fungi, or a virus) are found in the CSF sample. No tumor cells are present. |
| Appearance: | Blood in the CSF can result from bleeding (hemorrhage) in or around the spinal cord or brain. But it may also be caused by tiny blood vessels poked during the spinal tap. If a brain hemorrhage has occurred, the color of the CSF may change from red to yellow to brown over several days. Bleeding caused by the lumbar puncture itself will show more red blood cells in the first sample collected than in later samples. Cloudy CSF may mean an infection (such as meningitis or a brain abscess) is present. |
| Pressure: | High CSF pressure may occur as a result of swelling (edema) or bleeding (hemorrhage) in the brain, infection (such as meningitis), stroke, or other circulatory problems. Below-normal pressure may mean there is a CSF fluid leak. |
| Protein: | A high level of protein may be caused by bleeding in the CSF, a tumor or spread of a cancer from another area of the body, diabetes, infection, injury, Guillain-Barré syndrome, severe hypothyroidism, or other nerve diseases. An increase in antibodies (immune system proteins) may be caused by inflammation in people who have multiple sclerosis, immune system disorders, or bacterial and viral infections. |
| Glucose: | Low glucose levels in the CSF are abnormal and may be caused by bacterial meningitis. Viral meningitis doesn't often cause low glucose levels in the CSF. Brain hemorrhage may also cause low glucose levels several days after bleeding begins. Higher-than-normal glucose levels are often caused by diabetes. |
| Cell counts: | Red blood cells (RBCs) in the CSF can result from bleeding. High levels of white blood cells (WBCs) can be a sign of meningitis. |
| Other results: | Bacteria or other organisms in the CSF mean that an infection (such as syphilis) or disease is present. Bacterial markers (bacterial antigens) that show up are a sign of meningitis. Cultures or stains of the CSF may also help show the cause of meningitis or encephalitis. Identifying tumor cells can show that cancer is present. |
Your doctor may order other special tests on the CSF fluid depending on your symptoms and past health.
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