Definition and Overview

A lumbar puncture is a medical procedure that involves “puncturing” the lumbar region of the spine, usually to collect samples of cerebrospinal fluid. The process is sometimes known as a spinal tap.

The spine, which is also called the backbone, is composed of vertebrae, distributed into three sections. The cervical spine is made up of 7 vertebrae, which are found around the neck region. This part of the spine is also closest to the brain. In the middle is the thoracic region, which is in the chest area. More than ten vertebrae compose the thoracic spine. In the lowest part is the lumbar spine, which is sometimes referred to as the lower back and it has five vertebrae. Four vertebrae are fused together, creating the tailbone.

In the spine is also a hollow column known as the spinal canal. In it runs the spinal cord, which is a bundle of several nerves. These nerves act as a gateway for signals coming from and going to the brain. Without it, organs in the body will not function properly.

The brain and the spine are essential to life, and thus, they have to be protected as much as possible against any injury or disease. This job is taken care of by the cerebrospinal fluid (CSF), which has the same consistency as water in the body. The same fluid is responsible for maintaining just the right amount of pressure in the brain.

Nevertheless, the CSF should maintain some form of equilibrium if it needs to function correctly. For instance, sugar should be 50–75mg/dl. Protein, on the other hand, must be within 15–45mg/dl. It also has the presence of white blood cells while initial pressure should be 70–180mm. Take note, however, that range may be slightly different depending on the labs. Any deviation from these numbers, as well as other manifestations or symptoms in the body, could indicate a problem affecting the brain, spine, and the nervous system.

Who Should Undergo and Expected Results

A lumbar puncture or spinal tap may be performed to:

  • Diagnose cancer – a spinal tap is a form of biopsy in which a sample is obtained so that it can be studied for any presence of malignant cells. If there are cancer cells, it is possible that the primary cancer began in the brain or it is a secondary cancer, in which the cancer has already metastasized to the spine and the brain.

  • Determine infection – Meningitis, for instance, is a form of infection that is usually caused by pathogens such as bacteria and virus. A person who has meningitis may develop swelling in the brain, which may lead to damage and death of the tissue. Meningitis can be fatal, so early diagnosis through lumbar puncture is essential.

  • Measure values of its components – Certain conditions can be confirmed, ruled out, or evaluated using lumbar puncture. For instance, an increase in CSF pressure could mean a buildup of intracranial pressure, which means there is an elevated pressure in the skull. This can be due to a brain tumor (which can be either benign or malignant), brain aneurysm, hemorrhage, or traumatic brain injury. A higher-than-normal CSF protein may indicate diabetes, infection, or injury. On the other hand, lower values can also be attributed to certain health problems. A low CSF pressure may be caused by diabetic coma or tumor growing in the spine.

  • Apply anesthesia – Usually, surgeries require anesthesia, which can be general or local. In local anesthesia, the patient remains awake or aware but does not feel any sensation in certain parts of the body. The anesthesia may be delivered in the lumbar region, which can make the lower part of the body numb to the operation.

  • Provide medications – Drugs especially those that are intended for the lumbar spine may be best delivered directly to the affected area. In certain cases, chemotherapy is distributed through lumbar puncture.

The expected results depend on the reason for the procedure. Any deviation from the ideal values could indicate an existing condition or the risk of developing one. If it’s meant for anesthesia, it takes a few hours before the patient may regain movement of the body.

As for the test, it may take less than 30 minutes to complete, but the results may not be immediately available. Usually, if it’s meant to diagnose an infection like meningitis, the results typically come back within 2 days. Sometimes, if the problem is more complex, it can take weeks.

How Does the Procedure Work?

Before the procedure begins, the doctor assesses if the patient is an eligible candidate for it. It’s important the patient doesn’t have any blood-related disorder that may prevent clotting. He or she should also not be allergic to anesthetics.

The procedure can take place in an outpatient department or a hospital. The patient should be wearing a hospital gown for easy access of the lower back.

The lumbar area where the needle will go through is first cleansed and numbed with a topical anesthetic. The patient will either sit on a surface while leaning forward or lie on a table with the knees drawn up toward the chest. This way, the vertebrae will expand and inserting the needle is quicker and more convenient. Depending on the objective, medication may be delivered normally using a catheter or anesthetic is applied to numb the lower torso.

If the doctor is having a hard time, an imaging tool such as a scan may be used to guide the needle. If the patient is restless or anxious, sedation or even general anesthesia may be given.

After the process, the patient may go home, provided he or she doesn’t get involved in demanding physical activities. A medication may also be provided for minor side effects.

Possible Risks and Complications

Lumbar puncture is generally a very safe procedure since only trained doctors can perform it. Nevertheless, there are some tolerable side effects including a headache, which is experienced by more than 20% of the patients. This happens when some CSF comes in contact with tissues. There may also be discomfort during and after the test, especially in the back. The pain may travel toward the legs. Although it’s rare, bleeding and injury to the nerves can also develop.


  • Fischbach FT, Dunning MB III, eds. (2009). Manual of Laboratory and Diagnostic Tests, 8th ed. Philadelphia: Lippincott Williams and Wilkins.
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