A lumbar puncture, also referred to as LP, spinal tap, spinal puncture, or spinal fluid examination, can be a diagnostic or therapeutic test. Spinal fluid is removed from below the spinal cord through a needle placed in the back for laboratory analysis or to reduce pressure. The pressure within the spinal fluid column may be measured during the procedure with a pressure-sensing device. Spinal fluid after withdrawal is commonly evaluated for color, blood, cells, bacteria, cancer, sugar, protein, and evidence of inflammation.

A lumbar puncture can also be used to inject therapeutic agents such as anesthetics or chemotherapeutic medications.

Advantages: The LP allows doctors to look inside at the environment of the brain and spinal cord. The procedure is relatively easy to perform and inexpensive.

Disadvantages and complications: Headache, infection, and back or leg pain/tingling. Rarely, the spinal cord or another large artery or vein may be punctured. If a pressure difference exists between the brain and lumbar cistern, the LP may result in abrupt clinical decline and death.

Contraindications: Infection near the puncture site, evidence of a pressure differential between the cranial and lumbar cavities, severe degenerative spine disease.

Preparation: Prior to the procedure you should avoid large meals. A trip to the bathroom to relieve oneself is also advised. Anxious patients should warn their physician prior to the procedure so that anxiolytics/sedatives can be provided. Clothing should be lose and easily removed so that cleansing fluids used to sterilize the region during the procedure do not stain the garments.

The Procedure: The LP may be done either lying or sitting. The physician will first locate the space from which the spinal fluid will be withdrawn. Your back will be cleaned and sterilely draped. A local anesthetic, xylocaine, may be used to dull the feeling at the puncture site. After anesthesia takes effect, a spinal needle will be inserted into the space containing the spinal fluid. Pressure may now be measured and five to 20 ccs of fluid collected for analysis. The spinal needle is then removed, the site of the puncture is cleansed, and sterile gauze applied.

After the procedure: The most frequent complication of LP is headache from lowered cranial pressure. The headache can be minimized by remaining inactive and reclined the remainder of the day. Drinking caffeinated beverages in addition to water will assist in minimizing this complication. Headaches rarely persist for more than two days. After one week a continued headache occurring while upright requires attention. A procedure can be performed to alleviate the headache when needed.

Awaiting the results: The fluid from a spinal tap may take several weeks to completely analyze. Arrange with your physician a means of follow up for the LP results prior to departure from the clinic on the day of the spinal tap.