What is a lumbar puncture (spinal tap)?

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a spinal tap, is a procedure in which the fluid surrounding the spinal cord (called the cerebrospinal fluid or CSF) is withdrawn through a needle and examined in a laboratory.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
  • Give spinal anesthesia
  • Inject dye for an X-ray diagnostic test
  • Inject medication (such as Baclofen)

Testing the CSF can help your doctor diagnose disorders of the central nervous system (including multiple sclerosis) that may involve the brain, spinal cord, or their coverings (meninges).

When the CSF is examined in the laboratory, the following are evaluated:

  • The number and types of white blood cells
  • The level of glucose
  • The types and levels of proteins
  • The presence of bacteria, fungi or abnormal cells