title: Methylene Blue Injection as an Alternative to Antegrade Nephrostography to Assess Urinary Obstruction After Percutaneous Nephrolithotomy.
abstract: OBJECTIVE
  Percutaneous nephrolithotomy (PCNL) remains an effective treatment for large stones. When nephrostomy tube (NT) is left post operation, antegrade urine flow is often confirmed with antegrade nephrostography (ANG) before tube removal. We compare methylene blue (MB) test combined with NT capping trial against ANG to assess antegrade urine flow after PCNL.
  
  
  METHODS
  One hundred one consecutive patients undergoing PCNL were prospectively enrolled between 7/2014 and 4/2015. An NT cap was placed the morning of postoperative day 1 (POD1). Failure was defined as need to uncap the NT for any reason. Two hours after capping, 7cc MB was injected into the NT. Positive MB test was defined as presence of blue per bladder Foley. ANG was then performed to assess antegrade urine flow. NTs were removed before discharge home when antegrade flow was documented. Primary outcomes included presence of antegrade flow on ANG and NT removal before discharge home. Receiver operating characteristic (ROC) and areas (Area under the ROC [AUC]), as well as Cohen's kappa coefficient (κ), were calculated comparing agreement of capping trial, MB, and ANG with NT removal.
  
  
  RESULTS
  One hundred one subjects were included in this analysis. 52.9% were left-sided surgeries and 60.4% utilized lower pole punctures. On ROC areas evaluating tests for agreement with NT removal before discharge, MB AUC 0.71 (95% CI 0.60-0.83), capping trial AUC 0.66 (95% CI 0.57-0.75), combed capping trial and MB AUC 0.72 (95% CI 0.61-0.84), and ANG AUC 0.78 (95% CI 0.68-0.88). In predicting NT removal, ANG performed better than capping trial alone (p = 0.042), but no differences were seen between MB and ANG (p = 0.229), combining the capping trial with MB test and ANG (p = 0.266) or combined testing and MB alone (p = 0.972).
  
  
  CONCLUSIONS
  Combining capping trial with MB injection is similarly accurate for predicting NT removal after PCNL compared to ANG. Capping trial and MB may be used in combination to obviate the need for ANG.
authors.affiliation: 1 Department of Urology, University of California , San Francisco, California.
authors.forename: Matthew D
authors.initials: MD
authors.lastname: Truesdale
authors.affiliation: 1 Department of Urology, University of California , San Francisco, California.
authors.forename: Molly
authors.initials: M
authors.lastname: Elmer-Dewitt
authors.affiliation: 2 DMS StatLab, Data Methods and Systems Statistical Laboratory, University of Brescia , Brescia, Italy .
authors.forename: Marco
authors.initials: M
authors.lastname: Sandri
authors.affiliation: 1 Department of Urology, University of California , San Francisco, California.
authors.forename: Bogdana
authors.initials: B
authors.lastname: Schmidt
authors.affiliation: 1 Department of Urology, University of California , San Francisco, California.
authors.forename: Ian
authors.initials: I
authors.lastname: Metzler
authors.affiliation: 1 Department of Urology, University of California , San Francisco, California.
authors.forename: Adam
authors.initials: A
authors.lastname: Gadzinski
authors.affiliation: 1 Department of Urology, University of California , San Francisco, California.
authors.forename: Marshall L
authors.initials: ML
authors.lastname: Stoller
authors.affiliation: 1 Department of Urology, University of California , San Francisco, California.
authors.forename: Thomas
authors.initials: T
authors.lastname: Chi
mesh_terms: D005260:Female; D005471:Fluoroscopy; D006801:Humans; D007275:Injections, Intravenous; D008297:Male; D008751:Methylene Blue / Q000008:administration & dosage*; D008875:Middle Aged; D009403:Nephrostomy, Percutaneous; D011184:Postoperative Period; D011860:Radiography, Abdominal; D012680:Sensitivity and Specificity; D014545:Urinary Calculi / Q000000981:diagnostic imaging*
chemical_list: D008751:Methylene Blue