Health Tests

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Harvard Medical School


What Happens During the Test?

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 up and lean forward on a table.

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 thoroughly cleaned with an antiseptic solution. Medicine is injected through a small needle to numb the skin and the tissue underneath the skin in the area where the spinal needle will be inserted. This causes some very brief stinging.

The spinal needle is very thin. The doctor inserts the spinal needle into the spot between the vertebrae. The needle is slowly pushed forward until it reaches the spinal canal. The doctor stops when fluid begins to drip out of the spinal needle into a sterile test tube.

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 3045 minutes. The needle is in place for close to one minute.

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