Is there anyway to differentiate between a traumatic tap and an aneurysmal SAH?


    Is there anyway to differentiate between a traumatic tap and an aneurysmal SAH?

    There may be.



    Traumatic lumbar punctures occur in up to 30% of lumbar punctures. An observational, multicenter cohort study by Jeffrey Perry et. al. attempted to answer this question and enrolled sequential patients with acute non-traumatic headaches who: had a GCS of 15, were neurologically intact, and whose headache reached a peak intensity an hour after onset.

    Aneursymal SAH was defined as either blood in subarachnoid space on initial CT or xanthochromia or red blood cells in the final tube WITH aneurysm on cerebral angiography (CT, MR, or digital subtraction).


    1739 patients underwent LP.

    The median time from initial headache to LP was 17 hours.   

    641 patients having an abnormal LP defined as >1 x10^6 cells/L

    15 patients had aneurysmal SAH

    ROC curve analysis revealed that: >2000 x 10^6 cells/L or xanthochromia = 100% sensitivity and 91.2% specific for SAH.  


    TLDR: If you have a patient you are concerned may have a SAH and the following are true: negative CT head, no xanthochromia, and a LP that has less than 2000 x 10^6 cells/L you may not need additional testing.


    Source: Jeffrey J Perry et. al. Differentiation between traumatic tap and aneurysmal subarachnoid hemorrhage: prospective cohort. BMJ. January 3 2015.

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