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Lumbar Puncture

A lumbar puncture (LP), commonly referred to as a "spinal tap", is a relatively simple test performed on patients with suspected meningitis or encephalitis, suspected certain central nervous system bleeding (subarachnoid hemorrhage), or prolonged alteration of sensorium without explanation.

During an LP, the physician prepares the lower back with sterile cleaning solution and then injects a local anesthetic such as lidocaine. Patients are asked to maintain, with some assistance, the "fetal position" (lying on the side with the knees pulled up to the stomach and the chin pulled down towards the chest). Anxious, uncooperative or pediatric patients may require a sedative and/or gentle restraint. A spinal needle is inserted between two lumbar vertebrae and the pressure of the cerebrospinal fluid (CSF) is measured and a sample of CSF is carefully withdrawn from the spinal canal. It is important to note that at the level of the lower back, the physician is below the spinal cord. This fact increases the safety of the procedure.

CSF fluid is sent to the laboratory for cell count, biochemical analysis, staining, cultures, a battery of antigen tests to screen for common meningitides, and special studies (if required). The results of the antigen testing may be available in a few hours. Other special studies and cultures may take several days. Initial and subsequent results from this test are helpful in ruling in or excluding serious disorders of the central nervous system. Aside from a mild headache, complications of LP are relatively uncommon.

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