happens when the test is performed?
- Most patients wear a hospital gown. Typically, you lie on your
side with your knees curled up against your chest. In some cases,
the doctor asks you to sit on the bed or a table instead, leaning
forward against some pillows.
The doctor feels your back to locate your lower vertebrae and
feels the bones in the back of your pelvis. An area on your lower
back is cleaned with soap. Medicine is injected through a small
needle to numb the skin and the tissue underneath the skin in
the area from which the sample is to be removed. This causes
some very brief stinging.
A different needle is then placed in the same area and moved
forward until fluid can be obtained through it from the spinal
canal. Because the needle must be placed through a small opening
between two bones, the doctor must sometimes move the needle
in and out several times to locate the opening. Because of the
numbing medicine used in this area, most patients experience
only a sense of pressure from this movement. Occasionally some
patients do get a sharp feeling in the back or (rarely) in the
leg. Let your doctor know if you feel any pain.
Sometimes the doctor measures the pressure of the fluid before
taking a sample. The pressure is measured with a tube that looks
like a large thermometer held against the needle. The fluid sample
collected is usually less than three tablespoons. You will not
feel any discomfort when it is removed. After this, the needle
is taken out. Usually a Band-Aid is the only dressing necessary.
The whole lumbar puncture, including set-up time, takes 30-45
minutes. The needle is in place for close to one minute.