EBQ:Differentiation between traumatic tap and aneurysmal subarachnoid hemorrhage

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Complete Journal Club Article
Perry, J et al.. "Differentiation between traumatic tap and aneurysmal subarachnoid hemorrhage: prospective cohort study". BMJ. 2015. 18(350):epub.
PubMed Full text PDF

Clinical Question

  • Can cerebrospinal fluid from patients with acute headache after traumatic lumbar puncture be distinguished from subarachnoid hemorrhage?


  • No xanthochromia and red blood cell count < 2000 × 106/L can reasonably excludes the diagnosis of aneurysmal subarachnoid hemorrhage.

Major Points

  • In ruling out traumatic subarachnoid hemorrhage, the traumatic tap which causes blood to mix with cerebrospinal fluid can complicate the diagnosis of subarachnoid hemorrhage in up to 30% of LPs.[1]

This study was a predefined subsidy of the Canadian subarachnoid hemorrhage (SAH) rule and provides data to classify the likelihood of a subarachnoid hemorrhage based on LP results. Using a threshold of 2000x106/L in the final CSF tube provides for a sensitivity of 100% (CI 74.7-100%) and specificity of 91.2% (88.6-93.3%). For xanthochromia however the sensitivity was only 46.6% (CI 22-72.6%) for diagnosing subarachnoid. Combining the RBC threshold with xanthochromia the sensitivity for subarachnoid hemorrhage is 100%[2]

Study Design

  • Planned substudy from the prospective multi center cohort study, designed to derive and validate the Ottawa SAH (subarachnoid hemorrhage) rule
  • Conducted between November 2000 - December 2009
  • Multicenter at 12 canadian academic EDs



Patient Demographics

  • Mean Age: 43yo
  • Sex: 40% Men/60% Women

Inclusion Criteria

  • Age >15
  • Alert patients (GCS =15)
  • ED patents with acute non-traumatic headache undergoing LP to rule out subarachnoid hemorrhage
  • Within 14 days of headache onset

Exclusion Criteria

  • Recurrent headaches (3 or more with similar character/intensity over 6 month or greater period
  • Transfered from other hospital with confirmed subarachnoid
  • Presence of focal neurologic deficits or papilledema
  • History of
    • Subarachnoid hemorrhage
    • Aneurysm
    • VP shunt
    • Brain neoplasm


  • Computed tomography and/or lumbar puncture was performed at the discretion of the treating physician
    • Some LPs were performed before CT scans
  • Patients discharged without having both computed tomography imaging and a normal result on lumbar puncture were assessed by telephone interview one month and six months after assessment in the emergency department as well as a review of medical records to identify any recorded subarachnoid hemorrhage.
  • Patients without telephone follow-up or subsequent hospital encounters at the enrolling sites were further checked against the coroner’s records to identify any deaths compatible with subarachnoid hemorrhage


Subarachnoid hemorrhage definition:

  • Blood in the subarachnoid space on CT brain
  • Xanthochromia on examination of CSF
  • Red blood cells in the final tube of CSF fluid and aneurysm shown with cerebral angiography requiring any neurovascular intervention or resulting in death.

Normal LP = 1098 Abnormal LP = 641 (36.9%)

  • No aneurysmal subarachnoid = 626
  • Aneurysmal subarachnoid 15
  • Xanthochromia = 7
  • No Xanthochromia = 8

Primary Outcome

There were 15 (0.9%) patients with aneurysmal subarachnoid hemorrhage based on abnormal results of a lumbar puncture.

Secondary Outcomes

The presence of less than 2000 × 106/L red blood cells in addition to no xanthochromia excluded the diagnosis of aneurysmal subarachnoid hemorrhage

  • Sensitivity of 100% (95% confidence interval 74.7% to 100%)
  • Specificity of 91.2% (88.6% to 93.3%).

Subgroup analysis

Characteristics or patients in Canadian SAH Rule Study

All patients in the SAH Rule derivation and validation cohort[3]

  • Neck Pain or stiffness: 33.7%
  • Median time of headache onset to peak: 60 seconds
  • CT performed: 81.7%
  • Mean time from headache onset to LP: 18 hours
  • Median RBC count in last tube: 0
  • Aneurysmal subarachnoid hemorrhage: 3.5%

Characteristics of patients with abnormal LP

Positive xanthochromia

  • Aneurysmal subarachnoid hemorrhage: 46.6%
  • No Subarachnoid: 2.6%

Median RBC count in last tube (x106)

    • Aneurysmal subarachnoid: 28741
    • No subarachnoid: 20

Angiography rate

  • Aneurysmal subarachnoid hemorrhage: 15%
  • No subarachnoid: 64.5%

Criticisms & Further Discussion

  • Although this study is useful for defining the number of RBCs concerning for a SAH it does not help guide the workup for patients with a negative CT and positive lumbar puncture. There was also a great percentage of patients who underwent CT angiography for a small percentage of SAH.
  • A study by Gorchynski found that RBC counts ≤ 500 x106/L in the 4th CSF tube had a 100% negative predictive value for subarachnoid hemorrhage[4]
  • Caution should be used for assessing abscess of SAH based on the percentage drop in RBC count since the presence of SAH was demonstrated in patients with a 25% reduction of RBCs between the 1st and 4th tubes[5]

External Links


Funded by the Canadian Institutes of Health Research (grants: 67107, 153742), the Ontario Ministry of Health and Long Term Care, and the physicians of Ontario through the Physician’s Services Incorporated Foundation


  1. Gorchynski J, Oman J, Newton T. Interpretation of traumatic lumbar punctures in the setting of possible subarachnoid hemorrhage: who can be safely discharged? Cal J Emerg Med 2007;8:3–7.
  2. Perry JJ et al. Should spectrophotometry be used to identify xanthochromia in the cerebrospinal fluid of alert patients suspected of having subarachnoid hemorrhage? Stroke 2006;37:2467–72.
  3. Perry JJ. et al. Clinical decision rules to rule out subarachnoid hemorrhage for acute headache. JAMA. 2013 Sep 25;310(12):1248-55.
  4. Gorchynski J. et al. Interpretation of traumatic lumbar punctures in the setting of possible subarachnoid hemorrhage: who can be safely discharged? Cal J Emerg Med 2007;8:3–7.
  5. Heasley DC et al. Clearing of red blood cells in lumbar puncture does not rule out ruptured aneurysm in patients with suspected subarachnoid hemorrhage but negative head CT findings. Am J Neuroradiol 2005;26:820–4.