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Cassandra Faris - One of the best experts on this subject based on the ideXlab platform.
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in reply intraobserver and interobserver agreement in visual inspection for Xanthochromia implications for subarachnoid hemorrhage diagnosis computed tomography validation studies and the walton rule methodological mistake
Neurosurgery, 2014Co-Authors: Laurence A G Marshman, Ryan Duell, Donna Rudd, Ross Johnston, Cassandra FarisAbstract:[Extract] Dr Sabour presents a dialog that, we believe, would have benefited from a considered and temperate review before its precipitate submission. In particular, had the author deferred to have comprehensively digested our article, we feel that his accusation of a "methodological mistake" would probably have been withdrawn.
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intraobserver and interobserver agreement in visual inspection for Xanthochromia implications for subarachnoid hemorrhage diagnosis computed tomography validation studies and the walton rule
Neurosurgery, 2014Co-Authors: Laurence A G Marshman, Ryan Duell, Donna Rudd, Ross Johnston, Cassandra FarisAbstract: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.
Laurence A G Marshman - One of the best experts on this subject based on the ideXlab platform.
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in reply intraobserver and interobserver agreement in visual inspection for Xanthochromia implications for subarachnoid hemorrhage diagnosis computed tomography validation studies and the walton rule methodological mistake
Neurosurgery, 2014Co-Authors: Laurence A G Marshman, Ryan Duell, Donna Rudd, Ross Johnston, Cassandra FarisAbstract:[Extract] Dr Sabour presents a dialog that, we believe, would have benefited from a considered and temperate review before its precipitate submission. In particular, had the author deferred to have comprehensively digested our article, we feel that his accusation of a "methodological mistake" would probably have been withdrawn.
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intraobserver and interobserver agreement in visual inspection for Xanthochromia implications for subarachnoid hemorrhage diagnosis computed tomography validation studies and the walton rule
Neurosurgery, 2014Co-Authors: Laurence A G Marshman, Ryan Duell, Donna Rudd, Ross Johnston, Cassandra FarisAbstract: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.
Marco L A Sivilotti - One of the best experts on this subject based on the ideXlab platform.
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spontaneous subarachnoid hemorrhage a systematic review and meta analysis describing the diagnostic accuracy of history physical examination imaging and lumbar puncture with an exploration of test thresholds
Academic Emergency Medicine, 2016Co-Authors: Chris Carpenter, Adnan M Hussain, Michael J Ward, Gregory J Zipfel, Susan Fowler, Jesse M Pines, Marco L A SivilottiAbstract:Background Spontaneous subarachnoid hemorrhage (SAH) is a rare, but serious etiology of headache. The diagnosis of SAH is especially challenging in alert, neurologically intact patients, as missed or delayed diagnosis can be catastrophic. Objectives The objective was to perform a diagnostic accuracy systematic review and meta-analysis of history, physical examination, cerebrospinal fluid (CSF) tests, computed tomography (CT), and clinical decision rules for spontaneous SAH. A secondary objective was to delineate probability of disease thresholds for imaging and lumbar puncture (LP). Methods PubMed, Embase, Scopus, and research meeting abstracts were searched up to June 2015 for studies of emergency department patients with acute headache clinically concerning for spontaneous SAH. QUADAS-2 was used to assess study quality and, when appropriate, meta-analysis was conducted using random effects models. Outcomes were sensitivity, specificity, and positive (LR+) and negative (LR−) likelihood ratios. To identify test and treatment thresholds, we employed the Pauker-Kassirer method with Bernstein test indication curves using the summary estimates of diagnostic accuracy. Results A total of 5,022 publications were identified, of which 122 underwent full-text review; 22 studies were included (average SAH prevalence = 7.5%). Diagnostic studies differed in assessment of history and physical examination findings, CT technology, analytical techniques used to identify Xanthochromia, and criterion standards for SAH. Study quality by QUADAS-2 was variable; however, most had a relatively low risk of biases. A history of neck pain (LR+ = 4.1; 95% confidence interval [CI] = 2.2 to 7.6) and neck stiffness on physical examination (LR+ = 6.6; 95% CI = 4.0 to 11.0) were the individual findings most strongly associated with SAH. Combinations of findings may rule out SAH, yet promising clinical decision rules await external validation. Noncontrast cranial CT within 6 hours of headache onset accurately ruled in (LR+ = 230; 95% CI = 6 to 8,700) and ruled out SAH (LR− = 0.01; 95% CI = 0 to 0.04); CT beyond 6 hours had a LR− of 0.07 (95% CI = 0.01 to 0.61). CSF analyses had lower diagnostic accuracy, whether using red blood cell (RBC) count or Xanthochromia. At a threshold RBC count of 1,000 × 106/L, the LR+ was 5.7 (95% CI = 1.4 to 23) and LR− was 0.21 (95% CI = 0.03 to 1.7). Using the pooled estimates of diagnostic accuracy and testing risks and benefits, we estimate that LP only benefits CT-negative patients when the pre-LP probability of SAH is on the order of 5%, which corresponds to a pre-CT probability greater than 20%. Conclusions Less than one in 10 headache patients concerning for SAH are ultimately diagnosed with SAH in recent studies. While certain symptoms and signs increase or decrease the likelihood of SAH, no single characteristic is sufficient to rule in or rule out SAH. Within 6 hours of symptom onset, noncontrast cranial CT is highly accurate, while a negative CT beyond 6 hours substantially reduces the likelihood of SAH. LP appears to benefit relatively few patients within a narrow pretest probability range. With improvements in CT technology and an expanding body of evidence, test thresholds for LP may become more precise, obviating the need for a post-CT LP in more acute headache patients. Existing SAH clinical decision rules await external validation, but offer the potential to identify subsets most likely to benefit from post-CT LP, angiography, or no further testing.
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sensitivity of computed tomography performed within six hours of onset of headache for diagnosis of subarachnoid haemorrhage prospective cohort study
BMJ, 2011Co-Authors: Jeffrey J Perry, Marco L A Sivilotti, Ian G Stiell, Cheryl Symington, Michael J Bullard, Marcel Emond, Jane Sutherland, Andrew Worster, Corinne M Hohl, Jacques S LeeAbstract:Objective To measure the sensitivity of modern third generation computed tomography in emergency patients being evaluated for possible subarachnoid haemorrhage, especially when carried out within six hours of headache onset. Design Prospective cohort study. Setting 11 tertiary care emergency departments across Canada, 2000-9. Participants Neurologically intact adults with a new acute headache peaking in intensity within one hour of onset in whom a computed tomography was ordered by the treating physician to rule out subarachnoid haemorrhage. Main outcome measures Subarachnoid haemorrhage was defined by any of subarachnoid blood on computed tomography, Xanthochromia in cerebrospinal fluid, or any red blood cells in final tube of cerebrospinal fluid collected with positive results on cerebral angiography. Results Of the 3132 patients enrolled (mean age 45.1, 2571 (82.1%) with worst headache ever), 240 had subarachnoid haemorrhage (7.7%). The sensitivity of computed tomography overall for subarachnoid haemorrhage was 92.9% (95% confidence interval 89.0% to 95.5%), the specificity was 100% (99.9% to 100%), the negative predictive value was 99.4% (99.1% to 99.6%), and the positive predictive value was 100% (98.3% to 100%). For the 953 patients scanned within six hours of headache onset, all 121 patients with subarachnoid haemorrhage were identified by computed tomography, yielding a sensitivity of 100% (97.0% to 100.0%), specificity of 100% (99.5% to 100%), negative predictive value of 100% (99.5% to 100%), and positive predictive value of 100% (96.9% to 100%). Conclusion Modern third generation computed tomography is extremely sensitive in identifying subarachnoid haemorrhage when it is carried out within six hours of headache onset and interpreted by a qualified radiologist.
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high risk clinical characteristics for subarachnoid haemorrhage in patients with acute headache prospective cohort study
BMJ, 2010Co-Authors: Jeffrey J Perry, Marco L A Sivilotti, Ian G Stiell, Melodie Mortensen, Cheryl Symington, Michael J Bullard, Jane Sutherland, Jacques S Lee, Mary A Eisenhauer, Howard LesiukAbstract:Objective To identify high risk clinical characteristics for subarachnoid haemorrhage in neurologically intact patients with headache. Design Multicentre prospective cohort study over five years. Setting Six university affiliated tertiary care teaching hospitals in Canada. Data collected from November 2000 until November 2005. Participants Neurologically intact adults with a non-traumatic headache peaking within an hour. Main outcome measures Subarachnoid haemorrhage, as defined by any of subarachnoid haemorrhage on computed tomography of the head, Xanthochromia in the cerebrospinal fluid, or red blood cells in the final sample of cerebrospinal fluid with positive results on angiography. Physicians completed data collection forms before investigations. Results In the 1999 patients enrolled there were 130 cases of subarachnoid haemorrhage. Mean (range) age was 43.4 (16-93), 1207 (60.4%) were women, and 1546 (78.5%) reported that it was the worst headache of their life. Thirteen of the variables collected on history and three on examination were reliable and associated with subarachnoid haemorrhage. We used recursive partitioning with different combinations of these variables to create three clinical decisions rules. All had 100% (95% confidence interval 97.1% to 100.0%) sensitivity with specificities from 28.4% to 38.8%. Use of any one of these rules would have lowered rates of investigation (computed tomography, lumbar puncture, or both) from the current 82.9% to between 63.7% and 73.5%. Conclusion Clinical characteristics can be predictive for subarachnoid haemorrhage. Practical and sensitive clinical decision rules can be used in patients with a headache peaking within an hour. Further study of these proposed decision rules, including prospective validation, could allow clinicians to be more selective and accurate when investigating patients with headache.
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should spectrophotometry be used to identify Xanthochromia in the cerebrospinal fluid of alert patients suspected of having subarachnoid hemorrhage
Stroke, 2006Co-Authors: Jeffrey J Perry, Marco L A Sivilotti, Ian G Stiell, George A Wells, Jenny Raymond, Melodie Mortensen, Cheryl SymingtonAbstract:Background and Purpose— The absence of Xanthochromia in the cerebrospinal fluid (CSF) is often used to exclude subarachnoid hemorrhage (SAH). Authorities advocate spectrophotometry to measure Xanthochromia, but most North American hospitals use visual inspection. We studied the diagnostic accuracy of spectrophotometry for SAH, and its potential impact on current practice. Methods— This was a prospective cohort study comparing the diagnostic accuracy of tests. The study was set in 3 university-affiliated tertiary care emergency departments. We enrolled consecutive neurologically intact adults with nontraumatic headache undergoing lumbar puncture (LP) to rule out SAH. CSF was centrifuged, frozen and analyzed later in batch. SAH was defined by (1) subarachnoid blood on CT, (2) >5×106 red blood cells/L in the final CSF tube and positive angiography, or (3) visible Xanthochromia in CSF and positive angiography. All subjects lacking a normal CT and LP were telephoned at 30 days. Results— We enrolled 220 patient...
Donna Rudd - One of the best experts on this subject based on the ideXlab platform.
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in reply intraobserver and interobserver agreement in visual inspection for Xanthochromia implications for subarachnoid hemorrhage diagnosis computed tomography validation studies and the walton rule methodological mistake
Neurosurgery, 2014Co-Authors: Laurence A G Marshman, Ryan Duell, Donna Rudd, Ross Johnston, Cassandra FarisAbstract:[Extract] Dr Sabour presents a dialog that, we believe, would have benefited from a considered and temperate review before its precipitate submission. In particular, had the author deferred to have comprehensively digested our article, we feel that his accusation of a "methodological mistake" would probably have been withdrawn.
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intraobserver and interobserver agreement in visual inspection for Xanthochromia implications for subarachnoid hemorrhage diagnosis computed tomography validation studies and the walton rule
Neurosurgery, 2014Co-Authors: Laurence A G Marshman, Ryan Duell, Donna Rudd, Ross Johnston, Cassandra FarisAbstract: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.
Ryan Duell - One of the best experts on this subject based on the ideXlab platform.
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in reply intraobserver and interobserver agreement in visual inspection for Xanthochromia implications for subarachnoid hemorrhage diagnosis computed tomography validation studies and the walton rule methodological mistake
Neurosurgery, 2014Co-Authors: Laurence A G Marshman, Ryan Duell, Donna Rudd, Ross Johnston, Cassandra FarisAbstract:[Extract] Dr Sabour presents a dialog that, we believe, would have benefited from a considered and temperate review before its precipitate submission. In particular, had the author deferred to have comprehensively digested our article, we feel that his accusation of a "methodological mistake" would probably have been withdrawn.
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intraobserver and interobserver agreement in visual inspection for Xanthochromia implications for subarachnoid hemorrhage diagnosis computed tomography validation studies and the walton rule
Neurosurgery, 2014Co-Authors: Laurence A G Marshman, Ryan Duell, Donna Rudd, Ross Johnston, Cassandra FarisAbstract: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.
