Guidance is needed on which CT-negative patients should proceed to LP for exclusion of SAH

As described by Goyale et al.,1 the role of lumbar puncture (LP) and cerebrospinal fluid (CSF) analysis for visual xanthochromia (and in the UK also for spectrophotometric detection of bilirubin) in cases of suspected subarachnoid haemorrhage (SAH) with non-diagnostic brain imaging has been a matter of conjecture over recent years. It is useful to know that there are some cases of aneurysmal SAH that are still diagnosed by CSF spectrophotometry, allowing vital treatment