Background: Postoperative urinary retention (POUR) is a known complication in the postanesthesia care unit (PACU). The variations in catheterization thresholds contribute to unnecessary invasive procedures. Objective: In the current study, we implemented an algorithm for a sterile intermittent catheterization (SIC) threshold of 800 ml with volume-dependent bladder scan intervals and compared the incidence of SIC with that of a matched patient cohort threshold of 400 ml. Design, setting, and participants: This comparative study of two prospective historical cohorts represented two thresholds for POUR, set at 400 ml without a standardized bladder scan protocol and 800 ml with a volume-dependent bladder scan protocol. Outcome measurements and statistical analysis: The primary outcome was the frequency of catheterization during the PACU stay. Secondary outcomes evaluated patient safety aspects in occurrence of thresholds above 400/800 ml. The study was set at the PACU under the Department of Anesthesia, Center for Cancer and Organ Diseases, Rigshospitalet, Denmark. Results and limitations: In total, 741 patients were consecutively included, with 307 in the POUR-400 and 434 in the POUR-800 group, and with comparable group characteristics. Significantly fewer patients fulfilled the SIC/catheter a’ demeure (CAD) criteria in the POUR-800 (5.0%) versus POUR-400 (14.3%) group, equivalent to a 65.0% relative reduction in SIC. Conclusions: Implementation of a standardized ultrasound-guided protocol with volume-dependent scan intervals and an evidence-based catheterization threshold of 800 ml decreases the need for SIC by >65%, without increasing the need for urinary catheterization at the wards. Patient summary: In this study, we implemented an algorithm for a sterile intermittent catheterization threshold of 800 ml with volume-dependent bladder scan intervals. A marked reduction was seen in catheterization in the postanesthesia care unit, without increasing catheterization rates at the ward. An algorithm for an intermittent catheterization threshold of 800 ml, with volume-dependent bladder scan intervals during patients’ stay at the postanesthesia care unit, reduces the incidence of urinary bladder catheterization. Extensive patient-clinician communication on bladder symptomatology is a crucial prerequisite.