Xanthochromia or yellow appearance of the cerebrospinal fluid (CSF) is often used to confirm suspected subarachnoid haemorrhage (SAH)(1,2). It is associated with the presence of bilirubin, a blood product that arises only in vivo by enzymatic transformation of hemoglobin. However, the visual assessment of CSF for xanthochromia is highly subjective, especially, in those frequent cases, when other blood products, such as oxyhemoglobin, are present due to a traumatic tap, which may make the CSF appear red (1,2). It may be further complicated by a high protein and cell count, such as occurs in minigitis and necrosis, or by the presence of other pigments, such as carotenoids, which may also alter CSF color. In order to distinguish pigments, such as bilirubin, in the CSF that are clinically important for diagnosing SAH and other intracerebral bleeds from those that are not, objective spectrophotometry rather than visual assessment is recommended (1). Because bilirubin has a characteristic signature – absorbance in the blue – it can be readily identified in the spectrophotometric trace, even in the presence of other pigments, where visual detection fails. This advantage can be demonstrated by standard procedures of specification for visual assessment known as colorimetry (6), which have been established by the Commission Internationale de l’Eclairage (CIE, the International Commission on Illumination). These procedures allow the trace to be converted to its chromaticity coordinates (6), which can be plotted in a geometric chart (the CIE 1931 chromaticity diagram for the 2° field of view), and for its dominant wavelength (corresponding to hue) to be defined with respect to average daylight conditions (CIE standard illuminant ‘D65’, see Figure). (New England Journal of Medicine. 2004 Oct 14;351(16):1695-6) Spectrophotometric analyses of 632 patient CSF samples, obtained at the National Hospital for Neurology & Neurosurgery between 01.1996 and 04.2004, indicated that 72 contained bilirubin. Of these, only 15 (21%) had bilirubin alone and were classified as 'pure yellow'(14%) or 'greenish yellow'(7%) by colorimetric analysis (see pie-chart inset in Figure. A significantly higher number, 57 (79%) had oxyhemoglobin as well as bilirubin present (Χ2=49.0, p<0.001). Their visual appearance, confirmed by colorimetric analysis, was not xanthochromic (see main Figure), but ranged from 'red' through 'reddish pink' to 'orange'. Thus, about 80% of CSF samples containing significant amounts of bilirubin are not perceived as typically xanthochromic, i.e.'yellow'. Equally importantly, the presence of bilirubin cannot be reliably excluded from CSF samples that appear visibly red. Yet, two recent surveys have shown that visual assessment of CSF samples for xanthochromia is still the most common method in America for detecting bilirubin and diagnosing/confirming SAH and other intracranial bleeds (2,3). This practice should be immediately re-evaluated. In the UK, visual assessment of CSF fell from 24% to 6%, whilst the use of spectrophotometry rose from 76% to 94%, following the introduction of new guidelines on detecting CSF pigments. This has reduced the estimated error rate from 40% to 9%(4). Clearly, visual assessment for xanthochromia, when compared with spectrophotometry, is an ambiguous and unreliable clinical procedure.
| mesh-term | fav. | com. | papers | rec. | reports | rec. | pen. | editor | |
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| 2 | 0 | 50904 | 12 | 4 | 4 | 0 | uclneaxel | ||
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| 1 | 0 | 451 | 0 | 4 | 4 | 0 | uclneaxel |
[pmid.15483297]
[meid:cerebrospinal fluid, csf, subarachnoid haemorrhage, sah, spectrophotometry, xanthochromia]
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