• 
• 

Three Part Question

Is the [Ottawa Subarachnoid Hemorrhage Rule] a sensitive and specific tool for predicting [Subarachnoid Hemorrhage] in [patients with headaches]?

Clinical Scenario

Headache is a common presenting complaint, but the incidence of subarachnoid hemorrhage is only about 9 per 100,000 patient-years. Is the Ottawa Subarachnoid Hemorrhage Rule a sensitive and specific clinical tool in predicting which patients merit further investigation with computed tomography?

Search Strategy

(Ottawa Subarachnoid Hemorrhage and (sensitiv$ or specific$) and (Subarachnoid hemorrhage or SAH or ICH or intracranial hemmorhage)).
Ovid Medline search limited to English and humans results

Search Outcome

4 search results were found, which are analyzed below. Further searching yielded 2 more relevant articles

Relevant Paper(s)

Author, date and country	Patient group	Study type (level of evidence)	Outcomes	Key results	Study Weaknesses
Pathan AS; Chakarova E; Tarique A. 2018 United Kingdom	Patients registered with headache in UK national health service from January to December 2016	Retrospective review	Sensitivity 100% (95% CI, 46.3 % - 100 %); specificity 44.2 % (95% CI, 36 % - 53 %); positive predictive value 6.02 % (95% CI 2.2 % - 14.1 %); negative predictive value of 100% (95% CI, 92.7 % - 100%)	Highly sensitive, weak specificity	Some incompletely documented patients excluded from analysis. Small sample size, only 5 documented SAH cases.
Micelle J. Haydel 2018 Canada	Patients meeting the inclusional criteria who attended 6 university-affiliated hospital emergency departments	Prospective cohort study	100% sensitivity and 14% specificity	Highly sensitive, Limited use in reduction of diagnostic testing	590 eligible patients missed by clinicians, thus not included in the study
Perry JJ; Sivilotti MLA; Sutherland J; Hohl CM; Emond M; Calder LA; Vaillancourt C; Thirganasambanda 2015 Feb USA	Patients attending the Emergency Department at the Mayo Clinic from January 2011 to November 2013	Retrospective review	sensitivity for SAH was 100% (95% CI, 62.9%-100%); specificity, 7.6% (95% CI, 5.4%-10.6%); positive predictive value, 2.1% (95% CI 1.0%-4.2%);negative predictive value, 100% (95% CI, 87.4%-100%)	High sensitivity, low specificity. Many patients w/ headache don't meet inclusional criteria	Only 9% of patients w/ headache fit the Ottawa SAH rule's inclusional criteria, many patients excluded, which may affect overall statistical accuracy.
Bellolio MF; Hess EP; Gilani WI; VanDyck TJ; Ostby SA; Schwarz JA; Lohse CM; Rabinstein AA. Nov 2018 Canada	Patients attending 6 Canadian emergency departments from January 2010 to January 2014	prospective cohort study	100% sensitivity (95% CI 94.6%-100%), specificity of 13.6% (95% CI 13.1%-15.8%)	Useful for ruling out SAH,	Only 1153 of 1743 eligible patients enrolled, the missing patients could affect results' accuracy.
Cheung HY, Lui CT, Tsui KL Dec 2018 Hong Kong	Patients presenting with headache from July 2013 to June 2016	retrospective cohort study	10% of the headache patients had SAH. 94% sensitivity. 32.9% specificity.	Adding vomiting & SBP > 160 to the OSHR imrp	Small sample size, only 500 patients
Jeffrey J. Perry, MD, MSc; Ian G. Stiell, MD, MSc; Marco L. A. Sivilotti, MD, MSc et al 2013 USA	Canadian tertiary care emergency departments attendees with headache from April 2006 to July 2010	Cohort Study	100% (95% CI, 97.2%-100.0%) sensitivity. 15.3% (95% CI, 13.8%-16.9%) specificity.	Highly sensitive, not specific

Comment(s)

4 Results were found from the Ovid Medline search, along with 2 additional results on further searching. All sources reported a high sensitivity 100%, but a low specificity (13.2-44%, average 19.7%). Therefore, the Ottawa Subarachnoid Hemorrhage Rule has a high negative predictive value, and can be used to rule out the need for further investigations. However, its low positive predictive value results in many patients without subarachnoid hemorrhages who are flagged for further investigation.

Clinical Bottom Line

The Ottawa Subarachnoid Haemorrhage Rule is a highly sensitive rule useful in aiding clinicians in ruling out the need for further investigation in patients who do not have fulfill any of the 6 criteria (neck stiffness, age > 40, witnessed loss of consciousness, thunderclap headache, limited neck extension, and onset during exertion). However, its high sensitivity comes at the price of low specificity, meaning that fulfilling any single factor alone is a poor predictor of having a subarachnoid haemorrhage. Thus, it may have limited value in lowering unnecessary investigations as compared to baseline clinical judgement. Further studies could be conducted to investigate whether the likelihood of subarachnoid haemorrhage increase with the fulfillment of multiple of the Ottawa Subarachnoid Haemorrhage Rule’s criteria.

References

1. Pathan AS; Chakarova E; Tarique A. To Head CT Scan or Not: The Clinical Quandary in Suspected Subarachnoid Hemorrhage; a Validation Study on Ottawa Subarachnoid Hemorrhage Rule Advanced Journal of Emergency Medicine 2018
2. Micelle J. Haydel In acute headache, the Ottawa Subarachnoid Hemorrhage rule had 100% sensitivity and 14% specificity Annals of Internal Medicine 2018
3. Bellolio MF; Hess EP; Gilani WI; VanDyck TJ; Ostby SA; Schwarz JA; Lohse CM; Rabinstein AA. External validation of the Ottawa subarachnoid hemorrhage clinical decision rule in patients with acute headache American Journal of Emergency Medicine 2015 Febuary
4. Bellolio MF; Hess EP; Gilani WI; VanDyck TJ; Ostby SA; Schwarz JA; Lohse CM; Rabinstein AA. Validation of the Ottawa Subarachnoid Hemorrhage Rule in patients with acute headache American Journal of Emergency Medicine 2017
5. Cheung HY, Lui CT, Tsui KL Validation and modification of the Ottawa subarachnoid haemorrhage rule in risk stratification of Asian Chinese patients with acute headache Hong Kong Medical Journal Dec 2018
6. Jeffrey J. Perry, MD, MSc; Ian G. Stiell, MD, MSc; Marco L. A. Sivilotti, MD, MSc et al Clinical Decision Rules to Rule Out Subarachnoid Hemorrhage for Acute Headache JAMA 2013; 1248-1255