Subarachnoid Hemorrhage: Sensitivity and Specificity

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

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 sensitivity and specificity 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.)

Fluid Test
Finding	Result	Sensitivity	Specificity
[ + ] CSF RBCs	+ 0 -	91%	85%
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
[ + ] Xanthochromia		Sensitivity = 57%
by visual inspection. 4-6 hours after onset. specificity not assessed Study: Neurocrit Care. 2005;2(2):99-109. PMID: 16159051
[ + ] Xanthochromia		Sensitivity = 65%
by visual inspection. 6-12 hours after onset. specificity not assessed. Study: Neurocrit Care. 2005;2(2):99-109. PMID: 16159051
[ + ] Xanthochromia		Sensitivity = 89%
by visual inspection. 12-24 hours after onset. specificity not assessed Study: Neurocrit Care. 2005;2(2):99-109. PMID: 16159051

Imaging
Finding	Result	Sensitivity	Specificity
[ + ] Non-contrast Head CT	+ 0 -	92%	100%
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
[ + ] Non-contrast Head CT		Sensitivity = 85%
3-days post onset. specificity not assessed Study: J Emerg Med. 2008 Apr;34(3):237-51. PMID: 18155383
[ + ] Non-contrast Head CT		Sensitivity = 50%
7 days post-onset. specificity not assessed Study: J Emerg Med. 2008 Apr;34(3):237-51. PMID: 18155383

History
Finding	Result	Sensitivity	Specificity
[ + ] Headache Location	+ 0 -	57%	62%
occipital in patients with thunderclap headache Study: Cephalalgia. 2002 Jun;22(5):354-60. PMID: 12110111
[ + ] Headache Location	+ 0 -	96%	29%
not temporal in patients with thunderclap headache Study: Cephalalgia. 2002 Jun;22(5):354-60. PMID: 12110111
[ + ] Headache Quality	+ 0 -	96%	25%
not "pressing" in patients with thunderclap headache Study: Cephalalgia. 2002 Jun;22(5):354-60. PMID: 12110111
[ + ] Headache Quality	+ 0 -	62%	53%
"exploding" in patients with thunderclap headache Study: Cephalalgia. 2002 Jun;22(5):354-60. PMID: 12110111
[ + ] Lack of Scotoma	+ 0 -	100%	7%
in patients with thunderclap headache Study: Cephalalgia. 2002 Jun;22(5):354-60. PMID: 12110111
[ + ] No History of Migraine	+ 0 -	79%	27%
either certain or probable migraines Study: Cephalalgia. 2002 Jun;22(5):354-60. PMID: 12110111
[ + ] Onset During Exercise	+ 0 -	40%	65%
or any strenuous activity (e.g. coitus) Study: Cephalalgia. 2002 Jun;22(5):354-60. PMID: 12110111
[ + ] Photophobia	+ 0 -	9%	96%
in patients with thunderclap headache Study: Cephalalgia. 2002 Jun;22(5):354-60. PMID: 12110111
[ + ] Worst Headache	+ 0 -	83%	36%
at onset in patients with thunderclap headache Study: Cephalalgia. 2002 Jun;22(5):354-60. PMID: 12110111

Physical Exam
Finding	Result	Sensitivity	Specificity
[ + ] Altered Mental Status	+ 0 -	17%	91%
in patients with thunderclap headache Study: Cephalalgia. 2002 Jun;22(5):354-60. PMID: 12110111
[ + ] Loss of Consciousness	+ 0 -	18%	96%
in patients with thunderclap headache Study: Cephalalgia. 2002 Jun;22(5):354-60. PMID: 12110111
[ + ] Neck Stiffness	+ 0 -	61%	90%
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
[ + ] Paralysis	+ 0 -	13%	97%
in patients with thunderclap headache Study: Cephalalgia. 2002 Jun;22(5):354-60. PMID: 12110111