Evaluation of 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, suspected spinal cord mass lesion, and a suspected intracranial mass lesion. Any bleeding diathesis should also be corrected prior to performing LP to prevent the possible occurrence of an epidural hematoma. A functional platelet count > 50,000/μL and an INR < 1.5 are advisable to perform LP safely.

Figure 4-2
Proper positioning of a patient in the lateral decubitus position. Note that the shoulders and hips are in a vertical plane; the torso is perpendicular to the bed. (From SE Strauss et al: JAMA 296:2012, 2006; with permission.)