Intraobserver and Interobserver Agreement in Visual Inspection for Xanthochromia: Implications for Subarachnoid Hemorrhage Diagnosis, Computed Tomography Validation Studies, and the Walton Rule BACKGROUND: Visual inspection for xanthochromia is used to diagnose subarachnoid hemorrhage (SAH), to validate computed tomography subarachnoid hemorrhage diagnosis and was used to determine the Walton rule. No study has assessed the reliability of xan- thochromia. OBJECTIVE: To determine intraobserver and interobserver xanthochromia agreement. METHODS: Mock cerebrospinal fluid samples contained increasing concentrations of human oxyhemoglobin, bilirubin, and albumin. Non-color-blind observers randomly assessed samples against a white background twice under significantly differing illu- mination. Specimens were recorded as red, orange, yellow, or clear. RESULTS: Results were obtained for 26 observers (11 male, 15 female observers). We found that 19.2% of samples were misclassified: red, 11.7%; orange, 28.5%; yellow, 29.6%; and clear, 22.1% (x 2 = 213.2; P , .001). Of the yellow misclassifications, 88% were mis- classified as clear. Female observers correctly classified samples significantly more fre- quently than male observers (P = .03). Intraobserver agreement differed significantly from expected for both male (x 2 = 105.6; P , .001) and female (x 2 = 99.9; P , .001) observers regardless of illumination. Interobserver agreement was poor regardless of sex (x 2 for male observers = 176.96, P , .001; x 2 for female observers = 182.69, P , .001) or illumination (x 2 for bright = 125.64, P , .001; x 2 for dark = 148.48, P , .001). Overall, there was 75% agreement in 46% of the tests and 90% agreement in only 36% of the tests. CONCLUSION: This simple laboratory study would be expected to maximize agreement relative to clinical practice. Although non-color-blind female observers significantly out- performed non-color-blind male observers, both intraobserver agreement and interob- server agreement for xanthochromia were prohibitively poor regardless of sex or illumination. Yellow was most frequently misclassified, 88% as clear (ie, true positives were commuted to false negatives). Xanthochromia is therefore highly unreliable for subarachnoid hemorrhage diagnosis and computed tomography validation. The Walton rule requires urgent clinical revalidation. KEY WORDS: Observer agreement, Xanthochromia Neurosurgery 74:395–400, 2014 DOI: 10.1227/NEU.0000000000000291 www.neurosurgery-online.com X anthochromia is the yellow hue present in the cerebrospinal fluid (CSF) supernatant of a patient with a recent subarachnoid hemorrhage (SAH) after centrifugation. Visual inspection for xanthochromia, the result of in vivo bilirubin formation from catabolized extruded oxyhemoglobin, has represented a diagnostic cri- terion for SAH since Froin’s discovery in 1903. 1 No study, however, has validated the absolute reliability of xanthochromia, whether intraob- server (observer consistency within the same sample) or interobserver (perceptual consistency across observers). Laurence A.G. Marshman, MD, FRCSN* Ryan Duell, MBBS* Donna Rudd, BSc‡ Ross Johnston, BSc (Hons)§ Cassandra Faris, MBBS* *Department of Neurosurgery, Institute of Surgery, The Townsville Hospital, Queens- land, Australia; Departments of ‡Physiology and, §Marine and Tropical Biology, James Cook University, Queensland, Australia Correspondence: Laurence A.G. Marshman, MD, FRCSN, Department of Neurosurgery, Institute of Surgery, IMB 20, PO Box 670, The Townsville Hospital, Douglas, Townsville 4810, Queensland, Australia. E-mail: l.a.g.marshman@btinternet.com Received, December 12, 2012. Accepted, December 29, 2013. Published Online, January 19, 2014. Copyright © 2014 by the Congress of Neurological Surgeons. Abbreviation: SAH, subarachnoid hemorrhage RESEARCH—LABORATORY TOPIC RESEARCH—LABORATORY NEUROSURGERY VOLUME 74 | NUMBER 4 | APRIL 2014 | 395 Copyright © Congress of Neurological Surgeons. Unauthorized reproduction of this article is prohibited. Downloaded from https://academic.oup.com/neurosurgery/article-abstract/74/4/395/2557445 by guest on 30 July 2018