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No LP after CT for SAH – Are we there yet?

July 14, 2016

Short Attention Span Summary

Could we finally be nearing a definitive answer as to whether LP is needed if CT is negative when working up possible SAH?  This meta-analysis found the prevalence of SAH in the 22 included studies was 7.5%.  CT without contrast within 6 hours was excellent at ruling in SAH (positive likelihood ratio [+LR] 230) and in ruling it out (negative LR 0.01).  This is outstanding, about as good as it gets for a diagnostic test.  For those with CT > 6 hours from headache onset, LP would only benefit if the post-CT probability of SAH was still 5% or more.  Although no history, physical exam finding, or clinical decision rule alone could rule out SAH, they could be helpful in stratifying which patients may have high enough risk to warrant LP with negative CT.

FOAM Report


Acad Emerg Med. 2016 Jun 16. doi: 10.1111/acem.12984. [Epub ahead of print]

Spontaneous Subarachnoid Hemorrhage: A Systematic Review and Meta-Analysis Describing the Diagnostic Accuracy of History, Physical Exam, Imaging, and Lumbar Puncture with an Exploration of Test Thresholds.

Carpenter CR1, Hussain AM2, Ward MJ3, Zipfel GJ4, Fowler S5, Pines JM6, Sivilotti ML7.

Author information:

1Emergency Medicine, Washington University in St. Louis School of Medicine.

2Department of Emergency Medicine, Northwestern University Feinberg School of Medicine.

3Emergency Medicine, Vanderbilt University.

4Neurosurgery, Washington University in St. Louis.

5Becker Medical Library, Washington University School of Medicine in St. Louis.

6Emergency Medicine, Center for Practice Innovation, George Washington University.

7Emergency Medicine and of Biomedical & Molecular Sciences, Queen’s University.



Spontaneous subarachnoid hemorrhage (SAH) is a rare, but serious etiology of headache. The diagnosis of SAH is especially challenging in alert, neurologically intact patients, as missed or delayed diagnosis can be catastrophic.


The objective was to perform a diagnostic accuracy systematic review and meta-analysis of history, physical examination, cerebrospinal fluid (CSF) tests, computed tomography (CT), and clinical decision rules for spontaneous SAH. A secondary objective was to delineate probability of disease thresholds for imaging and lumbar puncture (LP).


PubMed, Embase, Scopus, and research meeting abstracts were searched up to June 2015 for studies of emergency department patients with acute headache clinically concerning for spontaneous SAH. QUADAS-2 was used to assess study quality and, when appropriate, meta-analysis was conducted using random effects models. Outcomes were sensitivity, specificity, and positive (LR+) and negative (LR-) likelihood ratios. To identify test and treatment thresholds, we employed the Pauker-Kassirer method with Bernstein test indication curves using the summary estimates of diagnostic accuracy.


A total of 5,022 publications were identified, of which 122 underwent full-text review; 22 studies were included (average SAH prevalence = 7.5%). Diagnostic studies differed in assessment of history and physical examination findings, CT technology, analytical techniques used to identify xanthochromia, and criterion standards for SAH. Study quality by QUADAS-2 was variable; however, most had a relatively low risk of biases. A history of neck pain (LR+ = 4.1; 95% confidence interval [CI] = 2.2 to 7.6) and neck stiffness on physical examination (LR+ = 6.6; 95% CI = 4.0 to 11.0) were the individual findings most strongly associated with SAH. Combinations of findings may rule out SAH, yet promising clinical decision rules await external validation. Noncontrast cranial CT within 6 hours of headache onset accurately ruled in (LR+ = 230; 95% CI = 6 to 8,700) and ruled out SAH (LR- = 0.01; 95% CI = 0 to 0.04); CT beyond 6 hours had a LR- of 0.07 (95% CI = 0.01 to 0.61). CSF analyses had lower diagnostic accuracy, whether using red blood cell (RBC) count or xanthochromia. At a threshold RBC count of 1,000 × 106 /L, the LR+ was 5.7 (95% CI = 1.4 to 23) and LR- was 0.21 (95% CI = 0.03 to 1.7). Using the pooled estimates of diagnostic accuracy and testing risks and benefits, we estimate that LP only benefits CT-negative patients when the pre-LP probability of SAH is on the order of 5%, which corresponds to a pre-CT probability greater than 20%.


Less than one in 10 headache patients concerning for SAH are ultimately diagnosed with SAH in recent studies. While certain symptoms and signs increase or decrease the likelihood of SAH, no single characteristic is sufficient to rule in or rule out SAH. Within 6 hours of symptom onset, noncontrast cranial CT is highly accurate, while a negative CT beyond 6 hours substantially reduces the likelihood of SAH. LP appears to benefit relatively few patients within a narrow pretest probability range. With improvements in CT technology and an expanding body of evidence, test thresholds for LP may become more precise, obviating the need for a post-CT LP in more acute headache patients. Existing SAH clinical decision rules await external validation, but offer the potential to identify subsets most likely to benefit from post-CT LP, angiography, or no further testing. This article is protected by copyright. All rights reserved.

This article is protected by copyright. All rights reserved.

PMID: 27306497 [PubMed – as supplied by publisher]

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