How to Differentiate Traumatic Lumbar Punctures from Aneurysmal Subarachnoid Hemorrhage

Authors: Perry JJ et al., BMJ 2015 Feb 18; 350:h568

The combination of a red blood cell count less than 2000 × 10^6/L and no xanthochromia is sufficient to rule out aneurysmal SAH in patients with traumatic lumbar punctures.

The diagnosis of subarachnoid hemorrhage (SAH) often requires lumbar puncture (NEJM JW Emerg Med Mar 2013 and Ann Emerg Med 2013; 62:1), however, in an estimated 10% to 30% of procedures that are traumatic, iatrogenic bleeding can complicate diagnosis. To identify cerebrospinal fluid characteristics that might differentiate between SAH and traumatic lumbar puncture, researchers conducted a planned substudy of a prospective multicenter study. They enrolled 1739 alert (Glasgow Coma Scale score, 15) patients older than 15 years with acute nontraumatic headache who underwent lumbar puncture to rule out SAH. Presence of aneurysmal SAH was determined by computed tomography (CT), CT angiography, or follow-up by phone at 1 and 6 months for patients who did not undergo CT angiography.

Lumbar puncture results were abnormal in 641 patients (37%). Of these, 15 (2%) had an aneurysmal SAH. Cerebrospinal fluid findings that distinguished between traumatic and true-positive lumbar puncture were a red blood cell (RBC) count greater than 2000 × 106/L and presence of xanthochromia. If neither of the criteria was present, 100% of aneurysmal SAHs were excluded.

Comment
If externally validated, these criteria — RBC count <2000 × 106/L and no xanthochromia — will greatly facilitate differentiation of traumatic lumbar puncture from SAH, and hopefully prevent the need for further evaluation due to iatrogenic complication.