title: Risk tolerance for the exclusion of potentially life-threatening diseases in the ED.
abstract: OBJECTIVE
  Given the same pretest probability (10%) for subarachnoid hemorrhage (SAH), pulmonary embolism (PE), and acute coronary syndrome (ACS), we determined if differences exist in the risk tolerance for disease exclusion according to published guidelines given a negative test result.
  
  
  METHODS
  Published guidelines that make practice recommendations on the evaluation of ACS, PE, and SAH were sought using the National Guideline Clearinghouse in low-risk settings. Second-order Monte Carlo simulation was performed to determine point estimates and confidence intervals (CIs) for posttest probabilities assuming a pretest probability of 10%.
  
  
  RESULTS
  Guidelines recommend that patients with low-risk suspected ACS should undergo stress testing. For SAH, computed tomography (CT) followed by lumbar puncture (LP) is recommended without mention of pretest probability; and D-dimer testing is recommended to exclude PE in low-risk patients. Test sensitivity for thallium-201 single photon emission computed tomography (SPECT) was 89%, exercise echocardiogram was 85%, D-dimer testing was 95%, and CT/LP for SAH was 100% (as a gold standard) and CT only was 97.5%. Given a negative test result, for PE, posttest probability was 0.5% (95% CI 0.1%-0.9%); for SPECT, 1.1% (SD 0.5%-1.6%); and for exercise echocardiogram, 1.5% (95% CI 0.5%-2.5%) compared with a posttest probability of 0% for CT followed by LP for SAH. Using a CT-only approach gives a posttest probability of 0.2% (95% CI 0.2%-0.4%).
  
  
  CONCLUSIONS
  Guidelines for suspected PE and ACS allow small but nonzero calculated risk end points in low-risk settings, whereas SAH guidelines afford no misses. Because many gold standard tests are more invasive and can have adverse effects, guideline authors should consider adopting a standard acceptable miss rate as an end point for workups with low clinical suspicion to avoid the overuse of invasive testing.
authors.affiliation: Department of Emergency Medicine, Hospital of the University of Pennsylvania, Philadelphia, PA 19104, USA. pinesjes@uphs.upenn.edu
authors.forename: Jesse M
authors.initials: JM
authors.lastname: Pines
authors.forename: Demian
authors.initials: D
authors.lastname: Szyld
mesh_terms: D015415:Biomarkers / Q000097:blood; D003937:Diagnosis, Differential; D004452:Echocardiography; D005080:Exercise Test; D005260:Female; D005338:Fibrin Fibrinogen Degradation Products / Q000032:analysis; D006801:Humans; D008297:Male; D009010:Monte Carlo Method; D009203:Myocardial Infarction / Q000175:diagnosis*; D017410:Practice Guidelines as Topic; D011237:Predictive Value of Tests; D011655:Pulmonary Embolism / Q000175:diagnosis*; D018570:Risk Assessment; D013129:Spinal Puncture; D013345:Subarachnoid Hemorrhage / Q000175:diagnosis*; D015899:Tomography, Emission-Computed, Single-Photon; D014057:Tomography, X-Ray Computed
chemical_list: D015415:Biomarkers; D005338:Fibrin Fibrinogen Degradation Products