Test Overview

A lumbar puncture (also called a spinal
tap) is a procedure to collect and look at the fluid (cerebrospinal fluid, or CSF) surrounding the brain and spinal cord.

During a
lumbar puncture, a needle is carefully inserted into the spinal canal low in
the back (lumbar area). Samples of CSF are collected. The samples are studied
for color, blood cell counts, protein, glucose, and other substances. Some of
the sample may be put into a container with a growth substance. This is called a culture. If any bacteria or
fungi grow in the culture, an infection may be present. The pressure of the CSF also is measured
during the procedure.

Why It Is Done

A
lumbar puncture 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 lumbar puncture 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 whether a disc or a cancer is bulging into the spinal
    canal.

In rare cases, a lumbar puncture may be used to lower the
pressure in the brain caused by too much CSF.

How To Prepare

Before you have a lumbar puncture, tell
your doctor if you:

  • Are taking any medicines. If you take medicines
    every day, ask your doctor whether you should take these medicines on the day
    of the lumbar puncture.
  • Are allergic to any medicines, such as
    those used to numb the skin (anesthetics).
  • Have had bleeding problems, or take a blood thinner, such as aspirin, clopidogrel (Plavix), or warfarin (Coumadin), or take over-the-counter medicines, such as ibuprofen (Advil, Motrin) or naproxen (Aleve). Your doctor will tell you when you should stop taking these medicines several days before your procedure. Make sure that you understand exactly what he or she wants you to do.
  • Are or might be pregnant.
  • Take any herbal
    remedies. Some of these remedies may thin the blood.

You will empty your bladder before the procedure.

You will be asked to sign a consent form that says you understand the risks of the test and agree to have it done.

Talk to
your doctor about any concerns you have regarding the need for the procedure,
its risks, how it will be done, or what the results will mean. To help you understand the importance of this test, fill out the medical test information form (What is a PDF document?).

How It Is Done

A lumbar puncture 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 lie on a
bed
on your side with your knees drawn 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.

The doctor also may look into your eyes using a special lighted scope (ophthalmoscope) to see if the pressure is high.

The
entire procedure takes about 30 minutes.

To lower your chance of
getting a headache following a lumbar puncture, 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. You may be told to drink extra
fluids after the procedure to help prevent or to reduce the severity of a
headache.

How It Feels

Some people find it uncomfortable to lie
curled up on their side. The soap may feel cold on your back. You will probably
feel a brief pinch or sting when the numbing medicine is given. You may feel a
brief pain when the spinal needle is inserted or repositioned.

During the procedure, the needle may touch one of your spinal nerves and
cause a tingling feeling, like a light electrical shock, running down one of
your legs.

You may feel
tired and have a mild backache the day after the procedure. Some people have
trouble sleeping for 1 to 2 days.

Risks

A lumbar puncture is generally a safe procedure.
In some cases, a leak of cerebrospinal fluid (CSF) may develop after a lumbar
puncture. Symptoms of this problem are a headache that does not go away after 1
to 2 days. A CSF leak can be treated with a blood “patch,” in which the
person’s own blood is injected into the area where the leak is occurring in
order to seal the leak.

Some people (10% to 25%) develop a headache after having a lumbar
puncture. Of those who do get headaches, only about half report that they are
severe. These headaches may last up to 48 hours and then go away on their own. Pain
medicine does not help control the headache, but lying flat in bed for several
hours after the procedure may help the headache.

About 1 out of 1,000 people who have a lumbar
puncture have a minor nerve injury. This heals on its own with time. Serious nerve injury is very rare. There is
also a small chance of infection of the CSF (meningitis), bleeding inside the
spinal canal, or damage to the cartilage between the vertebrae. Your doctor
will talk with you about these risks.

A lumbar puncture may cause serious problems for people
who have high pressure in the brain caused by a tumor, a pocket of infection in
the brain (abscess), or major bleeding inside the brain. Your
doctor will check your nervous system, spinal cord and brain before doing a
lumbar puncture. In some cases, a
computed tomography (CT) scan or
magnetic resonance imaging (MRI) scan may be done
before the lumbar puncture to know that it is safe to do the puncture.

After the procedure

Call your doctor immediately
if you have:

  • Chills or a fever.
  • A stiff neck.
    This may be a sign of a developing infection.
  • Any drainage or
    bleeding from the puncture site.
  • A severe
    headache.
  • Any numbness or loss of strength in your legs.

Results

A
lumbar puncture (also called a spinal tap) is a procedure to collect and look
at the fluid (cerebrospinal fluid, or CSF) surrounding the brain and
spinal cord. Many different tests can be done on the CSF. Some results will be
ready right away, some will take a few hours after the procedure, and others
will take several weeks.

The normal values listed here-called a reference range-are just a guide. These ranges vary from lab to lab, and your lab may have a different range for what’s normal. Your lab report should contain the range your lab uses. Also, your doctor will evaluate your results based on your health and other factors. This means that a value that falls outside the normal values listed here may still be normal for you or your lab.

Normal results footnote 1

Appearance:

CSF is normally
clear and colorless.

Pressure:

Normal CSF pressure in the
lower back for an adult ranges from 90-180 millimeters (mm) water. For
children younger than 8 years old, the normal opening pressure range is 80-100 mm water.

Protein:

The normal protein content of
CSF in an adult’s lower back (lumbar) region is 15-45
milligrams per deciliter (mg/dL) or 150-450 milligrams per liter (mg/L). Older adults
and children may have higher values that are still in the
normal range.

Glucose:

The normal range for CSF glucose
content for adults is 40-70 mg/dL or 2.2-3.9 millimoles per liter (mmol/L). For children, the normal range for glucose in CSF is 60-80 mg/dL or 3.3-4.4 mmol/L.

Cell counts:

Normal CSF contains no
red blood cells (RBCs). The
white blood cell (WBC) count for adults is 0-5 WBCs
per cubic millimeter (mm3). Children may normally
have a higher WBC count. No
neutrophils are present.

Other results:

No infectious organisms (such
as bacteria, fungi, or a virus) are found in the CSF sample. No tumor cells are
present.

Abnormal results

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 vessel 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 a blocked spinal canal.

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 does
not 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 indicate meningitis.

Other results:

Bacteria or other organisms in the CSF means that an infection (such as
syphilis) or disease is present. Bacterial markers
(bacterial
antigens) that show up mean meningitis. Cultures or
stains of the CSF may also help show the cause of meningitis or
encephalitis. Identifying tumor cells can show cancer is present.

Your doctor may order other special tests on the CSF fluid
depending on your symptoms and past health.

What Affects the Test

Reasons you may not be able to
have the procedure or why the results may not be helpful include:

  • Not being able to lie still during the
    procedure.
  • Having conditions such as
    obesity,
    dehydration, spinal disease, severe
    arthritis, or recent spinal surgery. These conditions
    may make it hard to do a lumbar puncture with the person lying down. The
    procedure may need to be done with the person sitting up and bent forward. In
    some cases, the procedure may need to be done with a special X-ray method
    called
    fluoroscopy. This is used to guide the placement of
    the spinal needle.
  • Bleeding into the cerebrospinal fluid (CSF). The
    needle puncture can cause bleeding into the CSF. Several samples of the fluid
    can show the difference between bleeding from the puncture and bleeding caused
    by a brain hemorrhage.
  • Not being able to collect a sample of the
    fluid. This is called a “dry tap.”

What To Think About

  • A lumbar puncture is not done if the person
    has:

    • A suspected tumor, swelling, or increased
      pressure in the brain. A
      computed tomography (CT) scan or
      magnetic resonance imaging (MRI) scan may be done
      first to see if it is safe to do the lumbar puncture.
    • A skin
      infection on the lower back. Doing a lumbar puncture in this case may allow the
      infection to spread into the spinal canal.
    • Bleeding disorders,
      which may increase the chance of bleeding during the procedure.
  • Other tests that may be done include:
    • A cisternal or ventricular puncture.
      Cerebrospinal fluid (CSF) can be collected from the upper spinal canal at the
      base of the skull (cisternal puncture) or from within the skull (ventricular
      puncture) when it is not possible to get CSF from the lumbar area. These
      procedures are done by a trained
      radiologist or neurosurgeon. Special X-ray methods are
      used to guide the placement of the needle.
    • Bacterial marker
      studies. In cases of suspected bacterial meningitis, bacterial marker
      (bacterial antigen) studies can quickly find the common types of bacteria that
      cause meningitis. Antibiotic treatment for that bacteria can be started
      immediately.

References

Citations

  1. Fischbach F, Dunning MB III (2015). A Manual of Laboratory and Diagnostic Tests, 9th ed. Philadelphia: Wolters Kluwer Health.

Other Works Consulted

  • Pagana KD, Pagana TJ (2014). Mosby’s Manual of Diagnostic and Laboratory Tests, 5th ed. St. Louis: Mosby.

Credits

ByHealthwise Staff
Primary Medical Reviewer E. Gregory Thompson, MD – Internal Medicine
Adam Husney, MD – Family Medicine

Current as ofOctober 9, 2017