Objectives: The aim of this study was to investigate the determination of ureteral stone impaction using acute phasereactants.Methods: A total of 110 patients who had a single ureteral stone treated during a single month using medical expulsivetherapy of tamsulosin 0.4 mg/day, diclofenac 75 mg upon analgesic requirement, and at least 3 liters fluid per day wereevaluated prospectively. The patients underwent ureteroscopy and were divided into 2 groups according to the presenceor absence of impaction. The preoperative white blood cell (WBC) count, red blood cell distribution width (RDW),C-reactive protein (CRP) level, erythrocyte sedimentation rate (ESR), mean platelet volume (MPV), and neutrophil-tolymphocyteratio (NLR) in the non-impacted stone group (Group 1; n=59) and the impacted group (Group 2; n=51)were statistically compared.Results: There was no statistically significant difference in terms of age, stone diameter, body mass index, grade of hydronephrosis,or stone localization between the 2 groups. The WBC, RDW, and MPV value differences were statisticallysignificant between the groups (p=0.035, p=0.035, and p=0.005, respectively). An MPV cut-off value of 9.55 fL was definedin Group 2 with 66% sensitivity and 62% specificity for impaction. There was no statistically significant differencebetween the groups in CRP, ESR, or NLR values (p=0.44, p=0.76, p=0.54, respectively).Conclusion: Evaluation of serum MPV with a cut-off value of 9.55 fL may predict ureteral stone impaction.