A spinal tap (also called a lumbar puncture) is a test that checks the health of the cerebrospinal fluid (CSF). This fluid surrounds the brain and spinal cord. During the test, a small sample of CSF is removed from the spinal canal to be tested in a lab. The test is safe and does not damage the spinal cord or nerves. Within a few hours your child's body will make new fluid to replace what is removed.