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Intraobserver and interobserver agreement in visual inspection for xanthochromia: implications for subarachnoid
Laurence A G Marshman1, Ryan Duell, Donna Rudd
1*Department of Neurosurgery, Institute of Surgery, The Townsville Hospital, Queensland, Australia; Departments of ‡Physiology and, §Marine and Tropical Biology, James Cook University, Queensland, Australia.
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 xanthochromia.
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 illumination. 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% (χ = 213.2; P < .001). Of the yellow misclassifications, 88% were misclassified as clear. Female observers correctly classified samples significantly more frequently than male observers (P = .03). Intraobserver agreement differed significantly from expected for both male (χ = 105.6; P < .001) and female (χ = 99.9; P < .001) observers regardless of illumination. Interobserver agreement was poor regardless of sex (χ for male observers = 176.96, P < .001; χ for female observers = 182.69, P < .001) or illumination (χ for bright = 125.64, P < .001; χ 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 outperformed non-color-blind male observers, both intraobserver agreement and interobserver 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.
