CSF spectrophotometry for bilirubin--why and how?

In patients presenting with a possible subarachnoid haemorrhage (SAH), a negative CT scan of the head does not exclude SAH and further investigations are therefore required. Cerebral angiography identifies aneurysms but does not inform on whether they have ruptured and is resource intensive. Examination of the CSF for blood cannot distinguish between an in-vivo bleed and a traumatic lumbar puncture. Visual inspection of the CSF supernatant fluid for xanthochromia is insensitive and should not be used on any account. The most appropriate investigation is spectrophotometry of the CSF for the haemoglobin breakdown products, oxyhaemoglobin and bilirubin. Guidelines for the performance of spectrophotometry and interpretation have been produced, modified and are reviewed here. From 5 years' data involving 2302 scans, 92% did not support the occurrence of SAH, 4% indicated the need for angiography to identify a possible aneurysm, while 4% were equivocal due to the presence of oxyhaemoglobin in sufficient concentrations to interfere with the ability to identify bilirubin reliably.