The spectrophotometric analysis of cerebrospinal fluid has an important role in the diagnosis of subarachnoid haemorrhage.¹ The presence of bilirubin, which is the basis for the laboratory identification of in vivo haemorrhage, is assessed by calculating the net bilirubin absorbance (NBA). Guidelines for this practice have recently been published.² To calculate the NBA, several measurement steps are required: locating the tangential points to construct a baseline; locating the 476-mm position on the scan to construct a perpendicular line; and measuring the distances between the baseline and peak, and correlating this with the distance measurement and absorbance magnitude …