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Timing of lumbar puncture in suspected sub arachnoid haemorrhage

Three Part Question

[In patients with suspected SAH but a negative CT scan] is [late LP (>12 hours) better than early LP] at [definitivly diagnosing SAH]?

Clinical Scenario

A 24 year old man presents to the emergency department (ED) with a sudden, severe occipital headache. He collapsed at the time of the initial headache but now feels better. He had a CT scan performed in the ED which was negative. He was subsequently referred to the medical team who performed a negative lumbar puncture (LP) 1 hour after admission (2 hours after the initial headache). This was negative and he was allowed home.
One week later he represents to the ED by ambulance following another collapse. He is GCS 3 on arrival and dies shortly afterwards. CT and postmortem reveal the casue of death to be subarachnoid haemmorhage.
You wonder if the LP was done too early to spot the original bleed.

Search Strategy

Medline 1966-10/04 using the Ovid interface.
[(exp subarachnoid hemorrhage OR OR subarachnoid AND (exp cerebrospinal fluid OR spinal OR exp spinal puncture OR lumbar OR AND ( OR tim$.mp)] LIMIT to human, English AND abstracts.

Search Outcome

Altogether 142 papers found of which 1 was relevant to the clinical question.

Relevant Paper(s)

Author, date and country Patient group Study type (level of evidence) Outcomes Key results Study Weaknesses
UK National External Quality Assessment Scheme for Immunochemistry Working Group.
Review of current recommendations for clinical biochemists in the UKReview articleTime for formation of bilirubin in CSFThis occurs 9-15 hours following a bleedNot systematic review Basic data on which recommendation not given
Selection of bilirubin as key determinantBilirubin is the only product of red cell lysis that occurs solely in vivo


It is common practice to withold LP until 12 hours following the headache onset. This is based on limited evidence from a small number of papers in this review. Most patients in studies of bilirubin biokinetics had positive CT scans. As LP is normally reserved for those patients with a negative CT scan they are arguably a different group. Despite these limitations current laborqatory work suggests that bilirubin will remain undetectable until 12 hours after symptom onset. This should remain the current practice. What is not shown from the literature is that any patient who had negative initial findings (on earky LP) followed by positive findings (on late LP). Such cases would provide a convincing argument, but none were found.

Clinical Bottom Line

In patients with suspected sub arachnoid bleeds, LP is not an adequate rule out strategy until 12 hours after the headache onset.

Level of Evidence

Level 2 - Studies considered were neither 1 or 3.


  1. UK National External Quality Assessment Scheme for Immunochemistry Working Group. National guidelines for analysis of cerebrospinal fluid for bilirubin in suspected subarachnoid haemorrhage. Ann Clin Biochem 2003:40;481-8.