Distinguishing traumatic lumbar puncture from true subarachnoid hemorrhage.

The lumbar puncture (LP) is a relatively simple diagnostic test. However, significant diagnostic ambiguity can arise when trauma from the needle causes bleeding into the subarachnoid space, especially when trying to make the diagnosis of subarachnoid hemorrhage (SAH). The purpose of this article is to assist emergency physicians in distinguishing traumatic LPs from SAH. To correctly interpret the findings of a traumatic tap, a few concepts must be understood. Timing of the LP in relation to the onset of the SAH affects the results of the cerebrospinal fluid (CFS) analysis; the typical findings will change with time. With a few caveats, xanthochromia, the yellow discoloration of the CSF resulting from hemoglobin catabolism, is often critical in making a diagnosis of SAH. A few of the most essential methods for distinguishing traumatic LP from true SAH include: the "three tube test," opening pressure, and inspection for visual xanthochromia.