title: Ultrasound evaluation of appendicitis: importance of the 3 × 2 table for outcome reporting.
abstract: BACKGROUND
  Despite a relatively high frequency of appendix nonvisualization when using ultrasound to diagnose appendicitis, many studies either fail to report these results or inconsistently analyze outcomes.
  
  
  OBJECTIVE
  The objective of this study is to determine the most transparent and accurate way of reporting and analyzing ultrasound results for the diagnosis of appendicitis.
  
  
  METHODS
  This was an observational cohort study of emergency department patients age 18 years or older who underwent right lower quadrant ultrasonography from September 2010 to October 2011. Patient characteristics, imaging, pathology, and follow-up data were analyzed. Test characteristics were calculated using conventional 2 × 2 contingency table analysis excluding inconclusive ultrasound results and an intention-to-diagnose approach with a 3 × 2 table.
  
  
  RESULTS
  Sixty-five patients were included. Forty-four (68%) patients had a nonvisualized appendix resulting in an overall diagnostic yield of 32%. Twenty-one patients had a visualized appendix (14 [22%] negative and 7 [11%] positive for appendicitis). Using 2 × 2 contingency table analysis, sensitivity and specificity were 100%. Using the 3 × 2 table with and the intention-to-diagnose principle, sensitivity was 70% and specificity was 25%. Three (7%) of 44 patients with a nonvisualized appendix had appendicitis (likelihood ratio = 0.40).
  
  
  CONCLUSIONS
  We suggest reporting ultrasound results using a 3 × 2 table (including nonvisualized findings) but using the traditional 2 × 2 type of analysis for test characteristic calculations. This approach allows for the determination of diagnostic yield and calculation of likelihood ratios when the appendix is not visualized. This approach to reporting should be considered for all types of diagnostic ultrasound studies.
authors: Department of Emergency Medicine, Mayo Clinic, Rochester, MN 55905.
authors: Martin
authors: M
authors: Fedko
authors: Department of Emergency Medicine, Mayo Clinic, Rochester, MN 55905. Electronic address: Bellamkonda.venkatesh@mayo.edu.
authors: Venkatesh R
authors: VR
authors: Bellamkonda
authors: Department of Emergency Medicine, Mayo Clinic, Rochester, MN 55905.
authors: M Fernanda
authors: MF
authors: Bellolio
authors: Department of Emergency Medicine, Mayo Clinic, Rochester, MN 55905.
authors: Erik P
authors: EP
authors: Hess
authors: Division of Biomedical Statistics and Informatics, Mayo Clinic, Rochester, MN 55905.
authors: Christine M
authors: CM
authors: Lohse
authors: Department of Emergency Medicine, Mayo Clinic, Rochester, MN 55905.
authors: Torrey A
authors: TA
authors: Laack
authors: Department of Emergency Medicine, Mayo Clinic, Rochester, MN 55905.
authors: Michael J
authors: MJ
authors: Laughlin
authors: Department of Emergency Medicine, Mayo Clinic, Rochester, MN 55905.
authors: Ronna L
authors: RL
authors: Campbell
mesh_terms: D000328:Adult; D001064:Appendicitis / Q000000981:diagnostic imaging*; D005260:Female; D006801:Humans; D008297:Male; D011237:Predictive Value of Tests; D012680:Sensitivity and Specificity; D014057:Tomography, X-Ray Computed; D014463:Ultrasonography