Lumbar Puncture (Spinal Tap)

Written by MaryAnn DePietro | Published on November 14, 2013
Medically Reviewed by George Krucik, MD, MBA on November 14, 2013

What Is a Lumbar Puncture?

A lumbar puncture is a medical procedure that is usually performed in order to obtain a sample of cerebrospinal fluid. The procedure is sometimes referred to as a spinal tap. Cerebrospinal fluid is the fluid that surrounds the spinal cord and brain. Characteristics of the spinal fluid can indicate certain medical conditions and infections.

What Does Lumbar Puncture Do?

A lumbar puncture may be done for a few different reasons. It is used to diagnose certain medical conditions, such as meningitis, myelitis, and demyelinating diseases (such as multiple sclerosis). In addition, the procedure can also diagnose cancers that affect the spinal cord and brain. Once obtained, the fluid is tested for the presence of protein and glucose, as well as for red and white blood cell levels. It is also analyzed to determine the presence of bacteria or a virus.

Who Benefits from a Lumbar Puncture?

Anyone who suspects a medical condition such as meningitis or encephalitis can benefit from a lumbar puncture. The quicker an accurate diagnosis is made, the sooner appropriate treatment can be started. Some conditions, such as bacterial meningitis, can be fatal if they are not treated quickly.

What Are the Side Effects of a Lumbar Puncture?

The most common side effect of a lumbar puncture is a headache (Harvard Medical School). Lying down for a few hours after the procedure may reduce the risk of developing a headache. Epidural blood patches can also be used to treat headaches after a lumbar puncture.

How Is a Lumbar Puncture Administered?

A lumbar puncture is performed with a needle and syringe. A tube is attached to the syringe in order to catch the spinal fluid.

The procedure usually takes about 45 minutes. The steps are:

  1. Positioning: The patient is positioned on his or her side.
  2. Sterilization: The back is then cleaned with an antiseptic solution to reduce the risk of infection.
  3. Numbing: The doctor numbs a section of the back by injecting a local anesthetic. In most cases, a patient can remain awake during the procedure.
  4. Fluid collection: After numbing, a hollow needle is injected into the subarachnoid space. The patient may feel some pressure at this point, but the procedure is usually not be painful. The cerebrospinal fluid then drips through the needle and into a test tube for collection and analysis.

After a small amount of fluid is collected, the needle is removed and the wound is bandaged. The patient is monitored for a short period for a headache or dizziness.

What Are the Benefits of Lumbar Puncture?

The main benefit of a lumbar puncture is that it allows a medical professional to make an accurate diagnosis of a medical condition or to rule a condition out. In some instances, the procedure is also used to administer medication directly into the spinal canal.

What Are the Risks of Lumbar Puncture?

According to Mayo Clinic, a lumbar puncture is safe, but there are some risks involved with the procedure, including:

  • infection
  • bleeding
  • reaction to anesthesia
  • nerve damage
  • brain herniation (rare)

How Does a Patient Prepare for Lumbar Puncture?

To prepare for a lumbar puncture, a medical history and exam is needed. Information on the types of medications a patient is taking is important, especially blood thinners since these can increase the risk of bleeding. A CT scan can also determine if any swelling is present around the brain.

What Is the Outlook for Lumbar Puncture?

There are usually no serious complications associated with a lumbar puncture. The procedure usually helps a physician to make a diagnosis or rule out a medical condition.

What Are the Results of Lumbar Puncture?

After the fluid is removed, it is sent to the lab for analysis. The results may take a few hours to a few days. The general appearance of the fluid is evaluated for cloudiness, which may indicate an infection. Determining the protein count and the presence of certain proteins can help a physician make a diagnosis. The white blood cell count will also be measured. A high count is also another sign of an infection. The results will also show whether any microorganisms were present in the fluid.

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