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Subarachnoid Hemorrhage: Likelihood Ratios

Introduction: For a decision rule to screen patients with acute headache, see BMJ. 2010 Oct 28;341:c5204. PMID: 21030443 .

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Tags: Neurologic Psychiatric Pulmonary testicular Toxic Trauma Vascular Tag this Diagnosis.

Prevalence

Population / CalculatorPrevalence Comments / Study / Link
Headaches in the emergency department 1% http://sinaiem.wordpress.com/2007/05/07/sah-update-are-new-ct-scanners-good-enough-to-obviate-the-lp/
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The likelihood ratios of findings for Subarachnoid Hemorrhage are listed below. See the left navigation bar to change the display.

Pre-Test Probability (Prevalence): %. Post-Test Probability (Predictive Value): %. Switch to display mode.
**Note that calculating probabilities from more than one finding is inherently inaccurate because findings are not independent. (For example, using two positive findings that share a common pathogenesis is likely to overestimate the true probability.)
Good Positive and Negative Likelihood Ratios
FindingResult +LR-LR
[ + ] Non-contrast Head CT + 0 - inf0.1
[ + ] CSF RBCs + 0 - 6.10.1
[ + ] Neck Stiffness + 0 - 6.10.4
Good Negative Likelihood Ratio
FindingResult +LR-LR
[ + ] Lack of Scotoma + 0 - 1.10
[ + ] Headache Location + 0 - 1.40.1
[ + ] Headache Quality + 0 - 1.30.2
[ + ] Worst Headache + 0 - 1.30.5
Good Positive Likelihood Ratio
FindingResult +LR-LR
[ + ] Paralysis + 0 - 4.30.9
[ + ] Loss of Consciousness + 0 - 4.30.9
[ + ] Photophobia + 0 - 2.31
Poorly Diagnostic Findings
FindingResult +LR-LR
[ + ] Altered Mental Status + 0 - 1.90.9
[ + ] Onset During Exercise + 0 - 1.20.9
[ + ] Headache Location + 0 - 1.50.7
[ + ] Headache Quality + 0 - 1.30.7
[ + ] No History of Migraine + 0 - 1.10.8
[ + ] Xanthochromia Sensitivity = 89%
[ + ] Non-contrast Head CT Sensitivity = 85%
[ + ] Xanthochromia Sensitivity = 65%
[ + ] Xanthochromia Sensitivity = 57%
[ + ] Non-contrast Head CT Sensitivity = 50%

 

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