Reference interval for the bilirubin excess in cerebrospinal fluid by derivative spectrophotometry

The value of the bilirubin excess can be a useful aid for recognizing blood from haemorrhage in cerebrospinal fluid. One of the parameters needed for the calculation of the bilirubin excess is the total bilirubin concentration in CSF. A method for measuring total bilirubin in cerebrospinal fluid is presented, based on diazotization of bilirubin according to Jendrassik-Gróf, combined with multiwavelength first derivative spectrophotometry. This bilirubin assay allows determination of total bilirubin concentrations as low as 0.045 +/- 0.002 mumols/l. This method also enables a correction for oxyhaemoglobin interference. The value of the bilirubin excess was calculated for patients (n = 66) not showing any neurological disorder. A reference interval of 0.07 +/- 0.06 mumols/l was calculated for the bilirubin excess.