Reducing the rate of negative ureteroscopy: predictive factors and the role of preoperative imaging.

Introduction: The aim of this study was to investigate factors that may predict a negative ureteroscopy (URS) performed for ureteric calculi in prestented patients and to assess preoperative imaging in reducing the rate of negative URS.

Methods: Data were collected on emergency stent placement for a ureteric calculus from April 2011 to February 2016 (Group A) and October 2016 to October 2019 (Group B). Data included patient demographics, indication for a stent, stone characteristics, baseline bloods, urine culture, readmission, negative URS rate and the use of pre-URS imaging. Multivariate logistic regression was used for statistical analysis.

Results: Of 257 patients who underwent emergency stent insertion, 251 underwent deferred URS for a ureteric calculus and 6 avoided URS due to pre-URS imaging. Indications for stent were pain (42%), sepsis (39%) and acute kidney injury (19%). Mean stone size was 7.8mm, mean stone density was 699 Hounsfield units (HU) and the stone locations were upper (62%), mid (13%) and lower ureter (25%). The overall negative URS rate was 12%. The negative URS rate was lower in patients with pre-URS imaging compared with those with none, 6% and 14%, respectively (OR=2.33, 95% CI: 0.69-7.56, =0.2214). Logistic regression analysis indicated stone size as the only significant predictor of a negative URS, where the greater the size of the stone the less likely URS would be negative (β=0.75, 95% CI: 0.60-0.94 =0.011).

Conclusions: Utilising pre-URS imaging can lead to a reduction in negative URS rate. Stone size <5mm appears to be the subgroup most likely to benefit from imaging.