title: The Absence of Gallstones on Point-of-Care Ultrasound Rules Out Acute Cholecystitis.
abstract: BACKGROUND
  Cholelithiasis affects an estimated 20 million people in the United States yearly; 20% of symptomatic patients will develop acute cholecystitis (AC). A recent single-center study estimating test characteristics of point-of-care ultrasonography (POCUS) for the detection of AC, as defined by gallstones plus sonographic Murphy's or pericholecystic fluid or gallbladder wall-thickening, resulted in a sensitivity and specificity of 87% (95% confidence interval [CI] 66-97) and 82% (95% CI 74-88), respectively. No prior studies have been conducted to estimate the test characteristics of POCUS for the purpose of excluding acute calculous cholecystitis.
  
  
  OBJECTIVE
  To determine whether the finding of gallstones alone on POCUS has high sensitivity, high negative predictive value, and low negative likelihood ratio for the exclusion of AC.
  
  
  METHODS
  We conducted an analysis using data from a prospective cross-sectional single-center study of POCUS test to estimate the test characteristics using a simplified definition of a positive test - the presence of gallstones alone. Clinical follow-up and pathology reports were used as the reference standard. Test characteristics were calculated and compared to the standard definition, gallstones plus one secondary finding.
  
  
  RESULTS
  The overall prevalence of AC was 14% (23 pathology-confirmed cases of 164 included patients). The sensitivity of the simplified definition was 100% (95% CI 85.7-100), negative predictive value 100% (95% CI 92.2-100), and negative likelihood ratio was < 0.1, compared to a sensitivity of 87% (95% CI 66-97%), negative predictive value 97% (95% CI 93-99%), and negative likelihood ratio of 0.16 (95% CI 0.06-0.5).
  
  
  CONCLUSIONS
  Simplifying the definition of the test findings on POCUS to gallstones alone has excellent sensitivity and negative predictive value for the exclusion of AC. This finding, if broadly validated prospectively, confirms the practice of excluding acute calculous cholecystitis using POCUS in emergency department patients.
authors.affiliation: Department of Emergency Medicine, University of California, San Francisco, San Francisco, California.
authors.forename: Julian
authors.initials: J
authors.lastname: Villar
authors.affiliation: Department of Emergency Medicine, University of California, Irvine, Orange, California.
authors.forename: Shane M
authors.initials: SM
authors.lastname: Summers
authors.affiliation: Department of Emergency Medicine, University of California, Irvine, Orange, California.
authors.forename: Michael D
authors.initials: MD
authors.lastname: Menchine
authors.affiliation: Department of Emergency Medicine, University of California, Irvine, Orange, California.
authors.forename: J Christian
authors.initials: JC
authors.lastname: Fox
authors.affiliation: Department of Emergency Medicine, University of California, San Francisco, San Francisco, California.
authors.forename: Ralph
authors.initials: R
authors.lastname: Wang
mesh_terms: D000328:Adult; D000368:Aged; D041881:Cholecystitis, Acute / Q000000981:diagnostic imaging*; D003430:Cross-Sectional Studies; D005260:Female; D005704:Gallbladder / Q000000981:diagnostic imaging; D042882:Gallstones / Q000000981:diagnostic imaging*; D006801:Humans; D008297:Male; D008875:Middle Aged; D019095:Point-of-Care Systems; D011237:Predictive Value of Tests; D011446:Prospective Studies; D012680:Sensitivity and Specificity; D014463:Ultrasonography
keywords: abdominal imaging; acute cholecystitis; cholelithiasis; emergency ultrasound; screening