Risk-benefit analysis of lumbar puncture to evaluate for nontraumatic subarachnoid hemorrhage in adult ED patients

Objective The objective of the study is to compare the risks and benefits of lumbar puncture (LP) to evaluate for subarachnoid hemorrhage (SAH) after a normal head computed tomographic (CT) scan. Methods This was an observational study of adult emergency department patients at a single hospital who presented with headache and underwent LP after a normal head CT to evaluate for SAH. Lumbar puncture results classified as indicating a SAH included xanthochromia in cerebrospinal fluid (CSF) or red blood cells in the final tube of CSF with an aneurysm or arteriovenous malformation on cerebral angiography. An LP-related complication was defined as hospitalization or a return visit due to symptoms attributed to the LP. Proportions of the study patients who had SAH diagnosed by LP and who experienced an LP-related complication were compared. Results The study included 302 patients, including 2 (0.66%) who were diagnosed with SAH based on LP (number needed to diagnose, 151); both of these patients had a known intracranial aneurysm. Eighteen (5.96%) patients experienced an LP-related complication (P <.01 compared with number with SAH diagnosed; number needed to harm, 17). Complications included 12 patients with low-pressure headaches, 4 with pain at the LP site, and 2 with contaminated CSF cultures. Conclusion The yield of LP for diagnosing SAH in adults with nontraumatic headache after a normal head CT was very low. The severity of LP-related complications was low, but complications were more common than SAH diagnoses. Lumbar puncture may not be advisable after a normal head CT to evaluate for SAH, particularly in patients with low-risk clinical features for SAH.