Factors and Cut-Off Predicting Stone Passage under Medical Expulsive Therapy (MET)

Background: Ureteral stones are the most common leading cause of acute flank pain. This study aimed to identify sociodemographic and clinical variables predicting spontaneous ureteral stone passage and determine the optimal size cut-off for predicting such passage. Method: We conducted a retrospective evaluation of patients presenting with acute renal colic at a urology outpatient clinic. Patients with ureteral stones ≤ 10 mm and no surgical intervention post-initial diagnosis, who attended follow-up visits, were included. Exclusion criteria comprised stone size > 1 cm, fever due to obstructive pyelonephritis, acute kidney injury, single kidney status, or bilateral ureteral obstruction. Results: Of 124 included patients, the spontaneous stone passage rate was 57.3%, with a mean passage time of 11.1 (SD 6.25) days. Bivariate analysis revealed that factors predicting spontaneous passage were stone size (p < 0.001), stone size below 7 mm (p < 0.0001), and stone location, particularly at the ureterovesical junction (UVJ) (p < 0.001). However, only stones with size < 7 mm had a significantly shorter passage time. Multivariate logistic regression confirmed these three factors as significantly associated with spontaneous passage, with stones at the UVJ showing an eightfold likelihood of passage (OR = 8.62, p = 0.009). ROC curve analysis suggested a stone size cutoff < 6.85mm was more likely to pass with MET with maximum sensitivity (78.9%) and specificity (71.1%) and area under the curve (AUC) of 0.832. Conclusions: Stone size < 7 mm, UVJ or distal ureter location, emerged as key predictors of stone passage in nephrolithiasis, and stone size below 6.85 mm is a reasonable cut off to initiate MET rather than 10 mm.