Q. My doctor said I need to have a spinal tap. What is this test, and why do I need it?
A. A spinal tap is used to get a sample of the cerebrospinal fluid that surrounds your spinal cord. The fluid is usually very clear, and 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.
Your doctor may do a spinal tap to check for bleeding, an increase in white blood cells, an increase in protein level, or inflammation. All of these are signs that you might have an infection, a tumor, or bleeding around your brain or spinal cord. To get the fluid sample, your doctor will insert a needle into your spinal canal in the lumbar region.