Lumbar Puncture (LP)

By Roberta Mitchell, RN, MSN, CPNP

(Spinal Tap, Spinal Puncture, CSF Collection)

Procedure Overview

What is a lumbar puncture?

A lumbar puncture (LP), also known as a spinal tap, is a diagnostic and/or therapeutic procedure performed by a physician. The procedure is performed by inserting a hollow needle into the subarachnoid space in the lumbar area (lower back) of the spinal column. The subarachnoid space is the canal in the spinal column that carries cerebrospinal fluid (CSF) between the brain and the spinal cord.

CSF is a clear fluid that bathes the brain and spinal cord while protecting it, like a cushion, from exterior injury. The fluid is produced and reabsorbed in the brain on a continuous basis. CSF is composed of cells, water, proteins, sugars, and other vital substances that are essential to maintain equilibrium in the nervous system.

Other related procedures that may be used to diagnose problems with the spine or brain include myelography (myelogram), computed tomography (CT scan), or magnetic resonance imaging (MRI). Please see these procedures for additional information.

Anatomy of the spine:

The spinal column is made up of 33 vertebrae that are separated by spongy disks and classified into distinct areas.

  • The cervical area consists of seven vertebrae in the neck.

  • The thoracic area consists of 12 vertebrae in the chest area.

  • The lumbar area consists of five vertebrae in the lower back area.

  • The sacrum has five, small fused vertebrae.

  • The four coccygeal vertebrae fuse to form one bone, called the coccyx or tailbone.

The spinal cord, a major part of the central nervous system, is located in the vertebral canal and reaches from the base of the skull to the upper part of the lower back. The bones of the spine and a sac containing cerebrospinal fluid surround it. The spinal cord carries sense and movement signals to and from the brain and controls many reflexes.

Reasons for the Procedure

A lumbar puncture may be performed for various reasons. The most common reason is to remove a small amount of CSF for examination and diagnosis of various disorders. CSF is tested for red and white blood cells, protein, glucose (sugar), clarity, color, and the presence of bacteria, viruses, or abnormal cells. Excess CSF may also be removed in patients who have an overproduction or decreased absorption of the fluid.

A lumbar puncture procedure may be helpful in diagnosing many diseases and disorders including, but not limited to, the following:

  • meningitis - an inflammation of the membrane covering the brain and spinal cord. The inflammation is usually the result of a viral, bacterial, or fungal infection, or the result of exposure to toxins or abnormal cells.

  • encephalitis - an inflammation of the brain that is usually caused by a virus.

  • certain cancers involving the brain and spinal cord

  • bleeding in the subarachnoid space

  • Reye syndrome - a potentially fatal disease that causes severe problems with the brain and other organs. Although the exact cause of the disease is not known, there has been an association between giving aspirin to children and the development of Reye syndrome. It is now advised not to give aspirin to children during illnesses, unless prescribed by your child's physician.

  • myelitis - an inflammation of the spinal cord or bone marrow.

  • neurosyphilis - a stage of syphilis during which the bacteria invades the central nervous system.

  • Guillain-Barré syndrome - a disorder in which the body's immune system attacks part of the nervous system.

  • demyelinating diseases - diseases that attack the protective coating that surrounds certain nerve fibers (e.g., multiple sclerosis or acute demyelination polyneuropathy).

In addition, a lumbar puncture may be used to measure the pressure of the CSF, which flows freely between the spinal column and the brain. The physician measures the pressure during a lumbar puncture using a special tube (called a manometer) that is attached to the lumbar puncture needle.

Finally, a lumbar puncture may be performed therapeutically to inject medications directly into the spinal cord. Some medications that may be given via lumbar puncture (intrathecally) include: spinal anesthetics before a surgical procedure, contrast dye for x-ray studies (e.g., myelography), or chemotherapeutic agents to treat cancer.