|Classification and external resources|
Xanthochromia [from the Greek xanthos (ξανθός)=yellow and chroma (χρώμα)=colour], is the yellowish appearance of cerebrospinal fluid (which envelops the brain) in particular medical conditions, especially subarachnoid hemorrhage. The most effective test for SAH is computed tomography (CT, a type of brain scan), but this identifies only 98% of cases in the first 12 hours after the symptoms and becomes less useful afterwards. Therefore, obtaining cerebrospinal fluid (after a CT scan) by lumbar puncture is recommended if someone has characteristic symptoms (e.g. a thunderclap headache) but no blood visible on the CT. According to one article it is not necessary if the images were taken with a third generation CT scan in the first six hours after the onset of the symptoms and no blood is present on the scan. However, this is not standard of care.
The yellow appearance is caused by red blood cells entering the CSF during the bleeding. The cells are eventually destroyed by the body, releasing their oxygen-carrying molecule heme, which is degraded by enzymes into the yellow-green pigment bilirubin. Heme from red blood cells that enter the CSF for a different reason, e.g., because a small blood vessel was damaged during the lumbar puncture (traumatic tap), has no time to be digested in this fashion, and bilirubin is therefore absent. Many laboratories rely on the color of the fluid alone when reporting the presence or absence of xanthochromia. Recent guidelines, however, suggest that spectrophotometry should be performed. This relies on the fact that bilirubin absorbs light of wavelengths between 450–460 nm. Two related substances that are also released when heme is metabolized are oxyhemoglobin and methemoglobin (the absorption ranges are 410-418 nm and 403-410 nm respectively) may also be detected during this process.
Xanthochromia is derived from the Greek word xanthos meaning yellow in chroma. Medically, it is used to denote patients that may suffer from subarachnoid Hemorrhage. Subarachnoid Hemorrhage occurs when abnormal blood vessels burst causing blood to fill the cavity between the brain and the skull eliciting severe pressure capable of inducing intense headaches, dizziness, vomiting, confusion and even death. Xanthochromia, specifically, relates to the color of chemically altered CSF fluid often present in people suspected of having cerebral trauma. Typically cerebrospinal fluid associated with Xanthochromia is yellow in appearance displaying absorption levels between 450 and 460 nm. 
Spectrophotometry in Xanthochromia Detection
Xanthochromia is in itself a unique condition that alters the visual appearance of CSF fluid. There are other sorts of pigment colors that can be found in the CSF which, also alter its visual appearance as well can denote a specific illness or condition. The distinct color of Xanthochromia (translucent Yellow) is a bi-product of blood entering the cerebrospinal column and infiltrating the contained CSF, known as Bilirubin (the degradation of heme). The formation of Bilirubin is significant as it declares the presence of Subarachnoid Hemorrhage via centrifuge exhibiting the yellowish Xanthochromic color. Although a CT scan has been proven to be about 98% effective and lumbar puncture more conclusive, for the two percent unaccounted by CT scans there are cases however when a computed tomography scan and or a lumbar puncture with visual inspection fail to show conclusive results regarding SAH.
Spectrophotometry, which is a quantified measurement of spectral transmission and of reflection properties as a function of wavelength, has proven to be more effective as a ‘fail safe’ in determining whether or not a patient is showing signs of SAH. Spectrophotometry functions on the idea that every color and material, or substance has its own distinct spectral transmittance. Every material has its own defining characteristics of which spectrophotometry can take into account via gloss, texture, color, and spatial attributes. Spectrophotometry has proven effective in determining whether a patient may have Xanthochromia, and subsequently SAH, as visual inspection via lumbar puncture may not always be conclusive. In most cases critical CSF samples are either contaminated by oxyhemoglobin or contain low levels of bilirubin. In regards to these conditions the detection of Xanthochromia becomes unreliable concerning visual inspection,predominantly when viewed under incandescent lighting or a tungsten desk lamp (corresponding to CIE standard illuminant A). spectophotometry allows for a calibrated uniform detection among samples that can determine the presence of Xanthochromia production in the CSF at even the smallest percentages of color saturation (about .62%).
Process and Controversy
The following serves as a sample experiment in the determination of Xanthochromia present in the CSF by use of spectrophotometry. The study was presented as a way to compare the effectiveness of visual discrimination with that of spectrophotometry. The study follows 11 participants from the clinical neurology staff within the Department of Neuroimmunology at the National Hospital for Neurology and Neurosurgery. The goal of the experiment was to compare visual inspection for Xanthochromia determination with determination via Spectrophotometry.
Methods and Trials
The premise behind the experiment was to create conditions in which the degradation of CSF could be observed, both through trials of visual inspection and through spectrophotometry. For the first simulation, the contamination of oxyhemoglobin was created with increasing dilutions of hemolysed blood. The second part of this experiment was to determine the lowest concentration of bilirubin capable of detection. Solutions containing incremented doubling dilutions of bilirubin were created in a series of test tubes for observation.
The participants (Practicing Clinical Neurology staff) were first asked to visual access the test tubes containing each solution of bilirubin or hemolysed blood in isolated CSF. The tubes were administered and observed by each of the 11 participants in random order to see if they could distinguish vials with bilirubin (denoted by Xanthochromic Color) from the vials with hemolysed blood (red or orange colored, infers blood contamination by lumbar puncture). 
After the visual assessment trials were administered each participant viewed scanned samples of each test tube using a Ultrospec 4300 pro spectrophotometer capable of scanning materials with wavelengths anywhere from 350 nm to 740 nm.
Evaluating Spectrophotometric Scans Through Colorimetry
To assess the spectrophotometric scans the xyY chromaticity coordinates were calculated. Chromaticity coordinates infer directly a chromaticity diagram and in that colorimetry, which has been set as a standard by the Commission Internationale de I’Eclairage (CIE) as a way to quantitatively define the physical human perception of color. Before the chromaticity coordinates can be derived the tristimulus values are created by multiplying the spectral reflectance of the scanned samples with the spectral concentration of the radiant power of the illuminating source (in this case the illuminant source was D65 ~ daylight and tungsten light ~ 3200 degrees K), along with color matching functions associated with the CIE standard colorimetric observer scaled by a constant value of k to set the absolute white point. A conversion from XYZ tristimulus values to chromaticity coordinates must then be employed.  Once plotted on the CIE 1931 chromaticity diagram the dominant Wavelengths (i.e. hue and excitation purities) and or saturation can be calculated. 
From the first series of samples (hemolysed blood in the CSF) obtained, viewed under illuminant D65, it was found that the dominant wavelength per sample ranged from about 572 nm denoting a “pure” yellow hue to 615 nm which denotes redder hues. These samples ranged from a high saturation of 97.9% to about 34.1%. The second series containing the bilirubin solutions in CSF were found spectrophometrically to all have a wavelength of 572 nm, but with varying degrees of saturation from .62% to about 36.6%.
The outcome of this experiment, specifically, showed that the 11 participants were able to confirm more precisely the presence of Xanthochromia in the CSF more accurately than by visual inspection. Spectrophotometry allows a more precise metric for Xanthochromia color determination as the inherent spectral distributions pertaining to degraded CSF fluid can be identified at even the smallest of concentrations, which may be unperceivable to the human eye.
Controversy over whether or not to identify Xanthochroma through spectrophotometry or via visual inspection persists however.
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- Journal of the New Zealand Medical Association 117 (Pt 1207). December 2004 http://journal.nzma.org.nz/journal/117-1207/1231/
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- Jonathan A. Edlow, Kathy S. Bruner, and Gary L. Horowitz (2002) Xanthochromia. Archives of Pathology & Laboratory Medicine: April 2002, Vol. 126, No. 4, pp. 413-415.
- Spectrophotometry. (2013, AUGUST 02). Retrieved from http://www.nist.gov/pml/div685/grp03/spectrophotometry.cfm
- Journal of the New Zealand Medical Association, 17-December-2004, Vol 117 No 1207
- Petzold A, Keir G, Sharpe TL. Why human color vision cannot reliably detect cerebrospinal fluid xanthochromia. Stroke.2005;36 :1295– 1297
- Williams, A. (2004). Xanthochromia in the cerebrospinal fluid. Practical Neurology, 4, 174-175. Retrieved from http://pn.bmj.com/content/4/3/174.full.pdf