Ottawa Subarachnoid Hemorrhage Rule a sensitive and specific tool for assessing headaches?
Date First Published:
December 23, 2019
Last Updated:
December 27, 2019
Report by:
Dorothy Law, Emergency Medicine Resident (Yan Chan Hosital )
Search checked by:
Dorothy Law, Yan Chan Hosital
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)).
Search Details:
Ovid Medline search limited to English and humans results
Outcome:
4 search results were found, which are analyzed below. Further searching yielded 2 more relevant articles
Relevant Paper(s):
| Study Title | Patient Group | Study type (level of evidence) | Outcomes | Key results | Study Weaknesses |
|---|---|---|---|---|---|
| To Head CT Scan or Not: The Clinical Quandary in Suspected Subarachnoid Hemorrhage; a Validation Study on Ottawa Subarachnoid Hemorrhage Rule 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. |
| In acute headache, the Ottawa Subarachnoid Hemorrhage rule had 100% sensitivity and 14% specificity 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 |
| External validation of the Ottawa subarachnoid hemorrhage clinical decision rule in patients with acute headache Bellolio MF; Hess EP; Gilani WI; VanDyck TJ; Ostby SA; Schwarz JA; Lohse CM; Rabinstein AA. 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. |
| Validation of the Ottawa Subarachnoid Hemorrhage Rule in patients with acute headache Bellolio MF; Hess EP; Gilani WI; VanDyck TJ; Ostby SA; Schwarz JA; Lohse CM; Rabinstein AA. Nov-18 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. |
| Validation and modification of the Ottawa subarachnoid haemorrhage rule in risk stratification of Asian Chinese patients with acute headache Cheung HY, Lui CT, Tsui KL Dec-18 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 |
| Clinical Decision Rules to Rule Out Subarachnoid Hemorrhage for Acute Headache 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 |
Author Commentary:
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.
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:
- 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
- Micelle J. Haydel. In acute headache, the Ottawa Subarachnoid Hemorrhage rule had 100% sensitivity and 14% specificity
- 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
- 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
- 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
- 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