Cerebrospinal fluid spectrophotometry of bilirubin, not the Xanthochromic Index, for the detection of CT-negative sub-arachnoid haemorrhage.

摘要

The paper by Wood et al.1 addresses a very important topic: what is the predictive value of cerebrospinal fluid (CSF) spectrophotometry in detecting CT-negative sub-arachnoid haemorrhage? Unfortunately the study is fundamentally flawed. Despite identifying that bilirubin is detected by spectrophotometry the authors use a 'Xanthochromic Index' that is based on measurement of the Soret band of oxyhaemoglobm at 415 nm. The Index was derived over 45 years ago and only takes account of bilirubin if the Index is >0.080. They refer to our work,3 criticising it for complicating matters, a charge we refute; and they fail to recognise that we emphasise the relevance of bilirubin measurement at the expense of haemoglobin and methaemoglobin, nor do they recognise that oxyhaemoglobm with an absorbance >0.1 can mask bilirubin, as traumatic taps are not always readily identifiable; this could easily lead to false negatives. Our guidelines were based on 740 scans with known outcome. It is possible from our figures to estimate the likelihood of detecting or missing an aneurysm. Our criteria for a positive bilirubin are based on those of Chalmers4 which allow for small but clinically significant increases to be detected.