By definition, xanthochromia is the yellow discoloration indicating the presence of bilirubin in the cerebrospinal fluid (CSF) and is used by some to differentiate in vivo subarachnoid haemorrhage from a traumatic lumbar puncture (LP) resulting in blood contamination of the CSF. While both in vivo haemorrhage and traumatic LP result in haemoglobin in the supernatant fluid, only in vivo haemorrhage results in bilirubin formation.
Following a true haemorrhage, red blood cells lyse and release oxyhaemoglobin, which is metabolised to bilirubin. The CSF supernatant after centrifugation is visibly pink or pink-orange due to oxyhaemoglobin, yellow due to bilirubin, and an intermediate colour if both are present together. The yellow colour due to bilirubin is the entity strictly defined as visible xanthochromia, as the term implies.
Chalmers and Kiley  published an improved method to determine xanthochromia in CSF which takes into account and compensates for the interference of haemoglobin and bilirubin absorption bands.
Figure 1: Molar Extinction Coefficient of Haemoglobin (left) and Bilirubin (right) [cm-1/M vs nm]
The method consists in scanning the region 350-550nm and printing the resulting spectrum. The analyst draws a tangent line from approx. 360nm to 530nm, which represents a corrected background of the spectrum. The height of haemoglobin and bilirubin bands is then measured by drawing two vertical lines between the corrected baseline and the apex of the corresponding peaks at 4