A spinal tap is a procedure in which a long needle is inserted into the spinal canal in the lower back to collect cerebrospinal fluid (CSF) for laboratory analysis. This clear, watery fluid circulates around the brain and spinal cord and is tested for:

• Protein. High levels of protein may be antibodies that indicate an infection or another condition.
  
  
• White blood cells. High levels of white blood cells may indicate infection.
  
  
• Glucose (blood sugar). Low levels of glucose may indicate infection.

Also known as a lumbar puncture, a spinal tap can be an outpatient procedure. However, the patient typically has to remain in the hospital for several hours afterward for monitoring. Although a spinal tap is not generally painful, it can cause discomfort. Children in particular may find the procedure to be uncomfortable and may have to be gently restrained during the test.

A spinal tap may not be recommended for certain patients, such as obese individuals, those who have had back surgery and pregnant women.

Spinal taps may be used to test for neurologic conditions including:

• Infections such as meningitis and encephalitis
  
  
• Bleeding around the brain (subarachnoid hemorrhage)
  
  
• Headaches caused by spinal fluid pressure that is too high or too low
  
  
• Cancers that affect the brain and spinal cord
  
  
• Movement disorders such as dystonia

A spinal tap, also called a lumbar puncture, removes a tiny amount of cerebrospinal fluid (CSF) for laboratory analysis. CSF is the clear, watery fluid that surrounds the brain and spinal cord. Spinal taps can be used to detect or treat various neurological disorders, and are also used to measure CSF pressure. Although a spinal tap is not generally painful, it can cause discomfort.

CSF forms in areas of the brain called ventricles and flows down into the area around the spinal cord. It is usually clear and contains small amounts of proteins and glucose (blood sugar). Its main function is to cushion and protect the brain and spinal cord by maintaining uniform pressure within the skull and spine.

Conditions related to neurology that may be diagnosed or treated with a spinal tap include:

• Viral or bacterial infections of the brain and spinal cord. These may include Lyme disease, encephalitis, meningitis, polio and neurosyphilis. Infections also can cause neurological symptoms and conditions such as apraxia, seizures, dementia, myoclonus and peripheral neuropathy.
  

  

• Headaches caused by spinal fluid pressure that is too high or too low.
  
  
• Bleeding around the brain (subarachnoid hemorrhage) and in the central nervous system.
  
  
• Central nervous system disorders characterized by tissue destruction, such as multiple sclerosis or various other nerve diseases. In addition, researchers have recently found that reduced concentrations in CSF of certain amyloid beta proteins may be an early indication of Alzheimer’s disease.

• Guillain-Barré syndrome. Disorder in which the body's immune system attacks part of the peripheral nervous system.
  
  
• Hydrocephalus. An abnormal accumulation of CSF within the skull, often referred to as “water on the brain.”
  
  
• Movement disorders such as dystonia.
  
  
• Myositis. Neuromuscular swelling of the muscles sometimes brought on by injury, infection or medicines.
  
  
• An obstruction in CSF circulation.
  
  
• Cancers that affect the brain and spinal cord. These include leukemia, lymphoma and retinoblastoma. 

Spinal taps are used to administer spinal anesthetic for some kinds of surgery. They are also sometimes used to administer chemotherapy medications designed to treat or prevent brain and central nervous system cancers. In this procedure, known as intrathecal chemotherapy, the drug is injected directly into the CSF and flows freely to the brain and spinal cord.

A spinal tap is usually performed in a hospital, although it can be performed in an outpatient surgical center in some cases. Prior to the procedure, patients will be asked to sign a consent form and should arrange for transportation. Patients should also be mentally prepared for the fact that they will have to lie flat for one to eight hours after the procedure. This helps prevent headaches that sometimes occur following a spinal tap.

Patients should follow their physician’s advice about any other preparatory steps before a spinal tap. These may include dietary restrictions and modifications to a patient’s regimen for over-the-counter and prescription medications.

Just prior to the procedure, patients are asked to remove all clothing, jewelry and glasses and to wear a hospital gown. The patient is then positioned with the back to the physician and rounded out, so that the spaces between the vertebrae are as wide as possible. The optimal position varies depending on the patient’s age. For example:

• Infants and small children. Lie on their sides curled up in a position that resembles the letter “C,” with their knees under their chin.
  
  
• Teens and adults. Lie on their sides with their knees drawn up to their chest and chin resting on their chest. 

Pillows will be positioned under the patient to support the spine. To help maintain this position, patients will be instructed to place one arm around their knees and the other around their neck. Although this position may be uncomfortable, it is vital that patients remain curled (to open up the space between the vertebrae) and still (to avoid injuring the spinal cord) during the procedure. Patients should also take care to breathe normally, because hyperventilation can skew pressure readings.

The area is first cleaned with an antibacterial solution and alcohol, and draped with sterile cloths to prevent any infection from getting into the spine. A local anesthetic is used to numb the area, which may cause an initial burning or stinging feeling. A small, hollow needle is inserted near the waistline (below the spinal cord) between the third and fourth lumbar vertebrae and into the spinal canal (arachnoid space).

The needle is pushed forward gently until the cerebrospinal fluid (CSF) is found. The needle may require some repositioning to locate the spinal canal. Patients will feel pressure as the needle is inserted and some brief pain as the needle penetrates the membranes (meninges) that cover the spinal cord and brain. This pain should dissipate after a few seconds, and the overall discomfort of this procedure is mild to moderate. If pain continues, patients should inform the physician performing the procedure because the needle may need to be repositioned.

The physician inserts a device called a manometer into the lumbar-puncture needle to measure the pressure of the CSF within the spinal canal. Two pressure readings are taken, one just after the initial puncture and another after the CSF has been withdrawn. One to two teaspoonfuls of fluid are then drawn into several sterile collection tubes and the needle is withdrawn. A bandage is placed on the injection site. The procedure usually takes at least 30 minutes.

Variations on the standard spinal tap procedure include:

• A sitting position may be used as an alternative, although it is rarely employed because the position is hard for patients to maintain, and movement could lead to complication or injury from the spinal tap. In the sitting position, patients sit straight and then bend their head and chest toward their knees.
  
  
• Infants will usually be held upright for a spinal tap.
  
  
• For patients with lower back problems who cannot use either the curled or sitting position, the needle may be inserted below the occipital bone at the back of the skull (cisternal puncture).

In extremely rare cases where the physician suspects an impending brain herniation (a condition that causes the brain to push through the opening at the back of the skull where the spinal cord is attached), the physician will drill a hole into the skull and insert a needle directly into the brain. This is called a ventricular puncture.

The amount of cerebrospinal fluid (CSF) removed by the spinal tap will be replaced by the body in about an hour. Some patients are prone to developing a headache after a spinal tap. To help prevent this, the physician may tell patients to lie flat in bed or with their head slightly raised at no more than a 30-degree elevation for several hours. However, this does not always prevent the headache and not all physicians make this recommendation. Drinking caffeinated beverages such as tea or coffee after the tap may also help relieve the headache.  

The physician may check the puncture site for redness, drainage or swelling prior to the patient being discharged. The physician may also perform a neurological assessment if the patient’s CSF pressure is elevated. This elevation in pressure could indicate an increase in intracranial pressure due to a cerebral hemorrhage, tumor or swelling (edema) caused by the physical trauma of the spinal tap itself.

After discharge, patients may gradually resume regular activities but should avoid driving and vigorous exercise for at least one day. During this time, patients should increase their intake of fluids and be cautious when performing any activity that requires moving the head or neck to avoid the most common side effect of this procedure, a post-spinal-tap headache.

Patients may feel mild discomfort or pain for a few days following the procedure, for which the physician may prescribe pain-relieving medications. Patients should contact their physician immediately if they:

• Notice any increased pain, swelling, redness, drainage or bleeding in the puncture area.
  
  
• Develop signs of infection, including headache, muscle aches, dizziness, fever, and/or neck rigidity and unusual irritability.
  
  
• Experience any nausea or vomiting.

The fluid sample is sent to a laboratory for analysis. The various tests include:

• Chemical composition of the fluid
  
  
• Identification of cells floating in the fluid, including any potentially cancerous cells
  
  
• Signs that the fluid is infected

In some cases, results can be available in as little as 30 minutes. In other cases, a physician may request a bacterial culture to look for organisms growing in the sample. It usually takes 48 to 72 hours to get these test results back.

Technicians who examine the fluid will note:

• General appearance. Cloudy spinal fluid can indicate increased cells and proteins suspended in the fluid, which is a sign of infection.
  
  
• Cell count. The number of red blood cells and number and type of white blood cells will be noted because normal spinal fluid does not contain significant numbers of these types of cells. Large numbers of white cells usually indicate an infection, whereas the presence of red blood cells may indicate cerebral hemorrhage.
  
  
• CSF gram stain and culture.  The spinal fluid is also stained and examined under the microscope to look for bacteria. To check for infection, the fluid is also cultured to see if any organisms grow from the fluid.
  
  
• Presence of substances such as:
  
  
• • Protein. High levels suggest hemorrhage, trauma, tumor, diabetes or polyneuritis (inflammation of several nerves). Conditions such as Guillain-Barré syndrome also are indicated by high levels of protein.
    
    
  • Glucose (blood sugar). Bacterial infections and hemorrhage often cause low glucose levels in the fluid.

High protein levels, low glucose levels, the presence of red blood cells and/or the appearance of blood in the CSF are indications of a hemorrhagic stroke caused by bleeding in the brain.

In most cases, spinal taps are relatively quick with mild discomfort and effective. The spinal cord is not affected, because the needle is usually inserted below the level where the cord ends.

As with any invasive procedure, there is a risk of infection with a spinal tap. In rare cases, patients develop meningitis, a bacterial or viral infection that causes inflammation of the meninges (the three membranes that cover the spinal cord and brain). Factors that increase the risk of complications from a spinal tap include alcoholism, a recent or chronic illness, a central nervous system infection or increased intracranial (within the skull) pressure. Other risks associated with the spinal tap include:

• Damage to the spinal cord, spinal canal or surrounding tissues by the spinal tap. The risk of this complication increases if the patient moves during the spinal tap.
  
  
• An allergic reaction to the anesthetic.
  
  
• Bleeding into the spinal canal.
  
  
• Brain herniation, an extremely rare and potentially fatal condition in which the brain pushes through the opening at the back of the skull where the spinal cord is attached.

In the case of a cisternal puncture or ventricular puncture, there is the additional risk of damage to the brain stem or brain tissue causing bleeding that could result in brain damage or death. Because of these risks, a spinal tap is the preferred method of collecting cerebrospinal fluid (CSF) for laboratory testing.

According to the National Institute of Neurological Disorders and Stroke (NINDS), about one-quarter of patients experience a post-spinal-tap headache within 48 hours of the spinal tap. Pain is typically centered near the forehead and/or the back of the head and may be accompanied by nausea, dizziness or tinnitus (ringing in the ears). It is usually more severe when sitting or standing than when lying down. The headache usually dissipates with bed rest, but if it persists or becomes more severe, patients should contact their physician immediately. This headache can last from a few days to a few weeks. 

The post-lumbar puncture headache can usually be avoided by remaining absolutely still during the spinal tap, drinking ample fluid afterward and limiting the movement of head and neck after the tap. Drinking caffeinated beverages such as tea or coffee after the tap may also help replenish cerebrospinal fluid and relieve the headache. The causes of a post-spinal-tap headache are unknown, but it may be the result of either leakage of the CSF or low CSF pressure in the spinal canal.

Patients with certain conditions may not be good candidates for a spinal tap, including:

• People who have had back surgery
• People with scoliosis (abnormal curvature of the spine)
• People who are obese
• Pregnant women
• Patients with a skin infection on the lower back
• People with bleeding disorders who take anticoagulant medication 

In such cases, an MRI (magnetic resonance imaging) or CAT scan (computed axial tomography scan) may be used instead of the spinal tap.

Preparing questions in advance can help patients have more meaningful discussions with healthcare professionals regarding their condition or test. Patients may wish to ask their doctor the following questions related to spinal taps:

1. Which conditions might I have that a spinal tap can help diagnose?
   
   
2. How does a spinal tap reveal the presence of these conditions?
   
   
3. Where exactly on my back will my spinal tap be performed?
   
   
4. Who will perform my procedure, and how experienced is this person in conducting spinal taps?
   
   
5. How can I prepare for the spinal tap?
   
   
6. How long does the procedure take? Am I likely to find it painful?
   
   
7. What are my chances of experiencing headaches after the procedure? What can I do to prevent a headache?
   
   
8. What risks does the procedure pose for me?
   
   
9. How long will I have to wait before my results come back?
   
   
10. What do my test results show? If I need treatment, what are my options?