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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Prevalence

Population / Calculator	Prevalence	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.

Good Positive and Negative Likelihood Ratios

Finding	+LR	-LR	Comments, Study
Non-contrast Head CT Duplicate	inf	0.1	patients presenting to ED with sever sudden-onset HA Sensitivity lower for subarachnoid blood confined to the posterior fossa or spinal cord. Study: J Emerg Med. 2008 Apr;34(3):237-51. PMID: 18155383
CSF RBCs	6.1	0.1	for specificity (i.e. vs traumatic tap), number is for >400/ul. Sensitivity is from 12-24 hours after onset. Study: Neurocrit Care. 2005;2(2):99-109. PMID: 16159051
Neck Stiffness	6.1	0.4	in patients with thunderclap headache alternate numbers: sens 30% spec 95% (BMJ. 2010 Oct 28;341:c5204. PMID: 21030443) Study: Cephalalgia. 2002 Jun;22(5):354-60. PMID: 12110111

Good Negative Likelihood Ratio

Finding	+LR	-LR	Comments, Study
Lack of Scotoma	1.1	0	in patients with thunderclap headache Study: Cephalalgia. 2002 Jun;22(5):354-60. PMID: 12110111
Headache Location Duplicate	1.4	0.1	not temporal in patients with thunderclap headache Study: Cephalalgia. 2002 Jun;22(5):354-60. PMID: 12110111
Headache Quality Duplicate	1.3	0.2	not "pressing" in patients with thunderclap headache Study: Cephalalgia. 2002 Jun;22(5):354-60. PMID: 12110111
Worst Headache	1.3	0.5	at onset in patients with thunderclap headache Study: Cephalalgia. 2002 Jun;22(5):354-60. PMID: 12110111

Good Positive Likelihood Ratio

Finding	+LR	-LR	Comments, Study
Paralysis	4.3	0.9	in patients with thunderclap headache Study: Cephalalgia. 2002 Jun;22(5):354-60. PMID: 12110111
Loss of Consciousness	4.3	0.9	in patients with thunderclap headache Study: Cephalalgia. 2002 Jun;22(5):354-60. PMID: 12110111
Photophobia	2.3	1	in patients with thunderclap headache Study: Cephalalgia. 2002 Jun;22(5):354-60. PMID: 12110111

Poorly Diagnostic Findings

Finding	+LR	-LR	Comments, Study
Altered Mental Status	1.9	0.9	in patients with thunderclap headache Study: Cephalalgia. 2002 Jun;22(5):354-60. PMID: 12110111
Onset During Exercise	1.2	0.9	or any strenuous activity (e.g. coitus) Study: Cephalalgia. 2002 Jun;22(5):354-60. PMID: 12110111
Headache Location Duplicate	1.5	0.7	occipital in patients with thunderclap headache Study: Cephalalgia. 2002 Jun;22(5):354-60. PMID: 12110111
Headache Quality Duplicate	1.3	0.7	"exploding" in patients with thunderclap headache Study: Cephalalgia. 2002 Jun;22(5):354-60. PMID: 12110111
No History of Migraine	1.1	0.8	either certain or probable migraines Study: Cephalalgia. 2002 Jun;22(5):354-60. PMID: 12110111
Xanthochromia Duplicate	Sensitivity = 89%		by visual inspection. 12-24 hours after onset. specificity not assessed Study: Neurocrit Care. 2005;2(2):99-109. PMID: 16159051
Non-contrast Head CT Duplicate	Sensitivity = 85%		3-days post onset. specificity not assessed Study: J Emerg Med. 2008 Apr;34(3):237-51. PMID: 18155383
Xanthochromia Duplicate	Sensitivity = 65%		by visual inspection. 6-12 hours after onset. specificity not assessed. Study: Neurocrit Care. 2005;2(2):99-109. PMID: 16159051
Xanthochromia Duplicate	Sensitivity = 57%		by visual inspection. 4-6 hours after onset. specificity not assessed Study: Neurocrit Care. 2005;2(2):99-109. PMID: 16159051
Non-contrast Head CT Duplicate	Sensitivity = 50%		7 days post-onset. specificity not assessed Study: J Emerg Med. 2008 Apr;34(3):237-51. PMID: 18155383