What it is: A spinal tap is done to take a sample of spinal fluid and reading of the spinal fluid pressure. A spinal tap is also necessary if you are having a myelogram. The spinal tap is most commonly done to look for infection, cancers, and bleeding into the brain or spinal cord.
What the test shows: A spinal tap is done in order to get a sample of the cerebrospinal fluid that surrounds the spinal cord. The fluid is usually very clear; it contains proteins, sugar, and other substances that can be found in blood. It typically does not contain red blood cells or many white blood cells. A spinal tap checks the pressure and content of the fluid. Signals that there may be problems include: evidence of bleeding, an increase in white blood cells (infection fighting cells, dead cells are "pus"), an increase in protein level, or inflammation. This could mean infection, tumors, or a hemorrhage around the brain or spinal cord.
What the test does not show: The spinal tap does not show much information about most types of back pain. It is not helpful if the doctor thinks you may have arthritis of the spine, a herniated disc, or spinal stenosis.
How the test is done: To obtain the fluid sample, a needle will be inserted into the spinal canal in the lumbar region. The needle is inserted through the back, usually right in the middle between two of the vertebrae. You may be asked to sit and lean over or you may be asked to lie on your side. Before the spinal needle is placed through the skin, the back will be cleansed with an antiseptic and the skin will be numbed with lidocaine. The procedure usually takes only 10 - 15 minutes.
What risks the test has: A spinal tap has more risks associated with it than most other tests and is one of the reasons that doctors prefer to use the "non-invasive" tests, such as the MRI and CAT scans, first. The risks associated with a spinal tap include infection of the spinal fluid (meningitis) and the possibility of developing a spinal headache. There is also a very small chance that the needle will cause bleeding around the spinal sac. This is more of a risk if you are on medications that thin the blood and interfere with blood clotting. If possible, you should not take aspirin or ibuprofen for five days before having a spinal tap. Tell your doctor if you are taking any type of blood thinners.
What the test costs: A spinal tap usually has several costs associated with the test. The first cost is the fee for actually doing the test. This is called the "technical fee". The second cost is the fee of having a specialist, such as a neurologist or spine specialist, perform and interpret the test. This is called the "professional fee". There may also be laboratory tests done on the fluid removed during the spinal tap. You may get several bills for this test: one from the hospital or clinic where you had the spinal tap done, one from the specialist who performed the test, and possibly one for the lab tests.
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