A spinal tap is a procedure during 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 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 is 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 are used to diagnose several conditions, including:

• Infections such as meningitis, encephalitis, Lyme disease and polio
  
  
• Bleeding around the brain (subarachnoid hemorrhage)
  
  
• Headaches caused by spinal fluid pressure that is too high or too low
  
  
• Certain nerve diseases
  
  
• Cancers that affect the brain and spinal cord