Xanthochromia

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Xanthochromia is the yellow appearance of cerebrospinal fluid (which envelops the brain) in particular medical conditions, especially subarachnoid hemorrhage.cite journal |author=Cruickshank A, Auld P, Beetham R, "et al" |title=Revised national guidelines for analysis of cerebrospinal fluid for bilirubin in suspected subarachnoid haemorrhage |journal=Ann. Clin. Biochem. |volume=45 |issue=Pt 3 |pages=238–44 |year=2008 |month=May |pmid=18482910 |doi=10.1258/acb.2008.007257 |url=http://acb.rsmjournals.com/cgi/content/full/45/3/238] 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 by lumbar puncture is recommended if someone has characteristic symptoms (e.g. a thunderclap headache) but no blood visible on the CT scan.

The yellow appearance is due to the fact that red blood cells entering the CSF during the bleeding are eventually destroyed by the body, and its oxygen carrying chemical heme 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, has no time to be digested in this fashion, and bilirubin is absent. Many laboratories rely on the color of the fluid alone when reporting the presence or absence of xanthochromia.cite web |author=Edlow JV | url=http://www.webmm.ahrq.gov/case.aspx?caseID=69 |title=The Worst Headache |publisher=Agency for Healthcare Research and Quality |work=Morbidity & Mortality Rounds on the Web |date=July 2004| accessdate=2008-06-22] 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.

There are other causes for xanthochromia.

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