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a spinal tap, is a procedure in which the fluid surrounding the spinal cord (called the cerebrospinal fluid or CSF) is withdrawn through a needle and examined in a laboratory.

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).

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).

Where is the need inserted in a lumbar puncture?

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.

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

Last reviewed by a Cleveland Clinic medical professional on 07/19/2014.


  • Radiologyinfo.org. Lumbar Puncture Accessed 11/19/2014.
  • CureSearch for Children’s Cancer. Lumbar Puncture (Spinal Tap) Accessed 11/19/2014.
  • Robbins E, Hauser SL. Chapter e46. Technique of Lumbar Puncture. In: Longo DL, Fauci AS, Kasper DL, Hauser SL, Jameson J, Loscalzo J. eds. Harrison's Principles of Internal Medicine, 18e. New York, NY: McGraw-Hill; 2012. library.ccf.org Accessed 11/19/2014.

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