Evaluation of cerebrospinal fluid (CSF) is essential for the diagnosis of suspected meningeal infection, subarachnoid hemorrhage, leptomeningeal neoplastic disease, and noninfectious meningitis. Relative contraindications to LP include local skin infection in the lumbar area and suspected intracranial or spinal cord mass lesion. Any bleeding diathesis should also be corrected prior to performing LP to prevent the possible occurrence of an epidural hematoma. Guidelines for performing LP in pts receiving anticoagulant or antiplatelet medications can be found in Chap. S9 of Harrison’s Principles of Internal Medicine, 20th edition. A functional platelet count >50,000/µL and an international normalized ratio (INR) <1.5 are advisable to perform LP safely.

In pts with an altered level of consciousness, focal neurologic deficits, or evidence of papilledema, an imaging study should generally be obtained prior to performing LP.