What is a lumbar puncture?

A lumbar puncture, also called a spinal tap, is a procedure in which the fluid surrounding the spinal cord (called the cerebrospinal fluid or CSF) is withdrawn through a needle and examined in a laboratory.

This procedure may be performed to:

  • Measure the pressure around the brain and spinal cord
  • Relieve pressure in the head and spinal canal
  • Give spinal anesthesia
  • Inject dye for an x-ray diagnostic test
  • Inject medications

There are seven cervical vertebrae in the neck, 12 thoracic vertebrae in the torso and five lumbar vertebrae in the lower back. The needle used in a lumbar puncture is usually inserted between the lumbar vertebrae.

The cerebrospinal fluid (CSF) circulates in the subarachnoid space of the spinal canal. The CSF has many vital functions, including protecting the brain and spinal cord from injury. The CSF contains glucose (sugar), proteins, and other substances that are also found in the blood. Testing the CSF can help in the diagnosis of disorders of the central nervous system that may involve the brain, spinal cord, or their coverings (meninges).