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What is Xanthochromia?

Xanthochromia means yellow-coloured. For most of the 20th century, samples of CSF were held up to light to see if the fluid was discoloured.

If yellow pigmentation was present the cerebrospinal fluid was discoloured on inspection and regarded as consistent with recent subarachnoid haemorrhage.

The term xanthochromia was felt to be the same as saying that subarachnoid haemorrhage had occurred.

Techniques for detecting bilirubin are now much more sophisticated than holding a specimen up to the light to look for "xanthochromia".

The gold standard is now spectrophotometry.

Spectrophotometry can now detect tiny amounts of bilirubin in a CSF sample.

The wavelength at which bilirubin absorbs electromagnetic radiation is 476 nanometres (see diagram below, right hand green vertical line).

Spectrophotometry tracing showing CSF bilirubin and oxyhaemoglobin peaks at 476 and 410 nanometres respectively

Bilirubin is a blood breakdown product, formed from oxidation of haem pigment (the pigment that makes your blood look red, and actually carries the oxygen molecules).

Bilirubin is also the pigment that makes a person with liver disease or haemolytic anamia go jaundiced (jaundice = yellow, yellow = xanth, yellow colour = xanthochromia!).

If you bled into your CSF, then your body will try to dissolve the blood though a chemical process called haemolysis.

One of the end products of haemolysis is bilirubin.

Outwith the body (in vitro) haem pigment will degrade to oxyhaemoglobin (peak is about 410 nanometres, left hand green line on diagram), but not bilirubin.

This is important, as it can help distinguish between blood that contaminated the CSF sample at the time of lumbar puncture, from blood that got there from the internal bleeding of a subarachnoid haemorrhage.

In subarachnoid haemorrhage, a mixture of oxyhaemoglobin and blirubin are detected, and a large amount of oxyhaemoglobin can obscure a small amount of bilirubin - beware of this (see 2008 Guidelines in Annals of Biochemistry).

Pitfalls in Bilirubin testing for Subarachnoid Haemorrhage

These are some other pitfalls for the unwary:

Make sure your sample is taken a minimum of 12 hours from the first onset of thunderclap headache.

Haem oxidase activity takes several hours to reach its peak.

So if you sample CSF too soon, you can get a false negative result - that is your lab result says no bilirubin, when in fact there was internal haemorrhage, but you just did not allow enough time for bilirubin to appear.

An old series from Newcastle, England published in 1956 by Turnbull, showed that in subarachnoid haemorrhage cases, xanthochromia always appeared if CSF was taken more than 12 hours from the onset of symptoms.

This series from 1956 led to the widely quoted statement that CSF analysis should wait at least 12 hours after onset of headache.

If you think the CSF was traumatic tap, collect 4 bottles sequentially for the lab, and label them 1, 2, 3 & 4.
Guidance on CSF sampling in subarachnoid haemorrhage has changed several times in the last 20 -30 years.
Previously, there was great care taken to number CSF bottles sequentially, and to carefully measure the red blood concentration in each.
If the numbers of red blood cells fell from bottle 1 to 3, then the CSF was felt to be "traumatic" from the actual procedure of needle insertion, and nothing to do with subarachnoid haemorrhage.
Then some research in the late 1980s demonstrated that counting red blood cells was unreliable, and didn't help tell if subarachnoid haemorrhage had occurred. So I have been preaching for years that there is no need to number CSF bottles !
More recently, the 2008 guidance has reversed back to the old method of numbering CSF bottles.
Instead of counting red blood cells which, these numbered bottles are for estimating CSF bilirubin and CSF oxyhaemoglobin.
Small amounts of bilirubin, which tell you internal bleeding has occurred, can be obscured by larger amounts of oxyhaemoglobin (remember that oxyhaemoglobin can form in the sample bottle and is not necessarily indicating haemorrhage from a dangerous headache disorder).
The theory behind reverting to numbered bottles is that you need to double check that small amounts of bilirubin were not overlooked by larger amounts of oxyhaemoglobin from "traumatic tap".
If you have traumatic tap, the amount of oxyhaemoglobin will fall from bottles 1 to 4, allowing greater confidence that you have not missed bilirubin.
It is important that you are as confident as possible that there is no bilirubin in the CSF of patients who have presented with thunderclap headache.
To miss a diagnosis of subarachnoid haemorrhage is potentially catastrophic for your patient, as a second bleed is often fatal or severely disabling.
Missed subarachnoid haemorrhage is one of the leading causes of litigation in neurological practice.
This is the 2008 guidance from Clinical Biochemists in the UK, to allow a decision to be made on whether high levels of oxyhaemoglobin are traumatic or represent recent bleeding.
As an absolute minimum, always try to send the last, and therefore cleanest, CSF sample for spectrophotometry.
Make sure your sample is protected from light before sending to the lab.

Spectrophotometry can detect 0.007 Absorption Units of bilirubin, and be reported as xanthochromia positive, and therefore indicate internal haemorrhage.

Below 0.007AU, CSF bilirubin is said to be negative. When exposed to Ultraviolet light, bilirubin in the CSF can degrade at a rate of 0.005AU per hour!

This means that a true positive sample with bilirubin of 0.011AU would become a false negative CSF if exposed to light for only one hour.