title: Predictors for negative ureteroscopy in the management of upper urinary tract stone disease.
abstract: OBJECTIVE
  To identify factors predictive of negative ureteroscopy (URS). Although computed tomography (CT) scans are sensitive in assessing upper tract calculi, there is increased effort to limit CT radiation exposure. On occasion, patients undergo URS and it is discovered that the stone has already passed.
  
  
  METHODS
  Retrospective chart review was conducted on all URS cases for renal and ureteral stones performed by a single surgeon from August 2003 to May 2008. Renal units were examined separately and excluded for stone size >10 mm, staged procedures, and previously placed ureteral stents. Negative URS cases were compared with those where stones were identified for differences in stone size, location, presence of preoperative pain, time interval since CT, presence of hydronephrosis, and use of medical expulsive therapy (MET).
  
  
  RESULTS
  Two-hundred fifty-six cases were identified. Twenty-five of 256 renal units (9.8%) did not have stones upon direct visualization. Stone size (P < .001) and stone location (P = .043) were significantly associated with outcome on univariate analysis. On multivariate analysis, only stone size was significant (P < .001).
  
  
  CONCLUSIONS
  Negative URS occurred in almost 10% of cases, with reasonable chance of spontaneous stone passage. Our data support smaller stone size and distal location as predictive of negative URS as opposed to preoperative pain, presence of hydronephrosis, and use of MET. Time interval since CT was not predictive. Rate of negative ureteroscopy is not insignificant, thus patients with small, distal stones who elect to undergo URS should be counseled regarding negative URS with an alternative being repeat imaging.
authors: Department of Urology, Boston University School of Medicine, Boston, MA, USA. Jessica.Kreshover@bmc.org
authors: Jessica E
authors: JE
authors: Kreshover
authors: Rian J
authors: RJ
authors: Dickstein
authors: Courtney
authors: C
authors: Rowe
authors: Richard K
authors: RK
authors: Babayan
authors: David S
authors: DS
authors: Wang