title: Determination of a Testing Threshold for Lumbar Puncture in the Diagnosis of Subarachnoid Hemorrhage after a Negative Head Computed Tomography: A Decision Analysis.
abstract: The objective was to determine the testing threshold for lumbar puncture (LP) in the evaluation of aneurysmal subarachnoid hemorrhage (SAH) after a negative head computed tomography (CT). As a secondary aim we sought to identify clinical variables that have the greatest impact on this threshold.
  
  
  
  A decision analytic model was developed to estimate the testing threshold for patients with normal neurologic findings, being evaluated for SAH, after a negative CT of the head. The testing threshold was calculated as the pretest probability of disease where the two strategies (LP or no LP) are balanced in terms of quality-adjusted life-years. Two-way and probabilistic sensitivity analyses (PSAs) were performed.
  
  
  
  For the base-case scenario the testing threshold for performing an LP after negative head CT was 4.3%. Results for the two-way sensitivity analyses demonstrated that the test threshold ranged from 1.9% to 15.6%, dominated by the uncertainty in the probability of death from initial missed SAH. In the PSA the mean testing threshold was 4.3% (95% confidence interval = 1.4% to 9.3%). Other significant variables in the model included probability of aneurysmal versus nonaneurysmal SAH after negative head CT, probability of long-term morbidity from initial missed SAH, and probability of renal failure from contrast-induced nephropathy.
  
  
  
  Our decision analysis results suggest a testing threshold for LP after negative CT to be approximately 4.3%, with a range of 1.4% to 9.3% on robust PSA. In light of these data, and considering the low probability of aneurysmal SAH after a negative CT, classical teaching and current guidelines addressing testing for SAH should be revisited.
authors.affiliation: Department of Emergency Medicine, Yale University School of Medicine, New Haven, CT. Richard.taylor@yale.edu.
authors.forename: Richard Andrew
authors.initials: RA
authors.lastname: Taylor
authors.affiliation: Departments of Emergency Medicine and Critical Care, Cleveland Clinic, Cleveland, OH.
authors.forename: Harman
authors.initials: H
authors.lastname: Singh Gill
authors.affiliation: Department of Emergency Medicine, Yale University School of Medicine, New Haven, CT.
authors.forename: Evie G
authors.initials: EG
authors.lastname: Marcolini
authors.affiliation: Duke University School of Medicine, Durham, NC.
authors.forename: H Pendell
authors.initials: HP
authors.lastname: Meyers
authors.affiliation: Department of Emergency Medicine, Icahn School of Medicine at Mount Sinai, New York, NY.
authors.forename: Jeremy Samuel
authors.initials: JS
authors.lastname: Faust
authors.affiliation: Department of Emergency Medicine, Icahn School of Medicine at Mount Sinai, New York, NY.
authors.forename: David H
authors.initials: DH
authors.lastname: Newman
mesh_terms: D003661:Decision Support Techniques; D004636:Emergency Service, Hospital; D006261:Headache / Q000209:etiology; D006801:Humans; D008875:Middle Aged; D059906:Neuroimaging; D012015:Reference Standards; D013129:Spinal Puncture / Q000592:standards*; D013345:Subarachnoid Hemorrhage / Q000175:diagnosis* / Q000000981:diagnostic imaging; D014057:Tomography, X-Ray Computed