A spinal tap, also known as a lumbar puncture, is a procedure in which a long thin needle is inserted into the spinal canal that surrounds the spinal cord. It is performed in the lower back to collect cerebrospinal fluid (CSF) for laboratory analysis. This clear, watery fluid circulates around the brain and spinal cord.

A spinal tap can be used to evaluate symptoms that may be caused by infection, inflammation or certain diseases. It can also help diagnose cancers, such as leukemias, lymphomas and carcinomas that have metastasized (spread) to the brain or spinal cord. After the CSF fluid has been extracted from a patient, it is examined for cancer cells.  

In cancer patients, a lumbar puncture also may be used for a procedure known as intrathecal (IT) chemotherapy. This form of treatment provides chemotherapy drugs directly into the cerebrospinal fluid. It is typically used to treat leukemia and other cancers, such as breast cancer or lymphomas that may have metastasized to the spinal cord or brain.     

A spinal tap is an outpatient procedure, meaning it does not require an overnight hospital stay. However, the patient typically has to remain in the hospital or outpatient surgical center for several hours afterward for monitoring. Although a spinal tap is not overly painful, it can cause discomfort. A local anesthetic is used to numb the areas prior to needle insertion.

Children in particular may find the procedure to be uncomfortable and may have to be gently restrained or mildly sedated during the test. A spinal tap may also be more uncomfortable for certain patients, including obese individuals, those who have had certain back surgeries and pregnant women. Physicians may recommend other procedures for these patients, such as magnetic resonance imaging (MRI) or computed tomography (CT) scan.