BACKGROUND: The blood transfusion chain is complex and error-prone. The key first step is patient registration for identification and linking to past medical and transfusion history. In Canada, transfusion-related errors are voluntarily reported to a national web-based database (Transfusion Error Surveillance System [TESS]). This project focuses specifically on the subset of registration errors impacting transfusion care in Canada. OBJECTIVE: To characterize registration-related transfusion errors in Canada between 2008 and 2017, including where, when, and why the errors occurred METHODS: A retrospective study was conducted on transfusion errors reported to TESS between January 2008 and December 2017. Errors reportable to TESS are defined as any deviation from standard operating procedures. Errors relating to patient registration and patient armbands were extracted. Data were available from 26 sentinel sites in three provinces. Volume of specimens received in the transfusion laboratory was used as denominator data where available. RESULTS: 554 errors pertaining to registration or patient armbands were reported, for a global error rate of 3.4/10,000 (range 0-18, median 1.4 [IQR 0-5.9]) (Figure 1). Errors were typically discovered before laboratory sample testing (n=222, 42%); 17% were discovered after product issue but before infusion (n=90). Errors most commonly occurred in outpatient clinics or procedure units (30% [range 0-100%]) and in emergency departments (24% [0%-100%]). The patient experienced a consequence in 11% (0%-75%) of errors but none resulted in transfusion reactions. The most frequent reports were name errors (29% [0%-100%]), duplicate patient registrations (27% [0%-100%]), and missing armbands (10% [0%-75%]) (Figure 2). CONCLUSION: Registration errors affect transfusion at every step and location in the hospital. Rates vary widely and differ by nature across sites. Further research into drivers of this heterogeneity is warranted to identify best preventative practices. This work was supported by the Public Health Agency of Canada and the Canadian Blood Services Program Support Award. Figure 1. Rate of error was calculated for sites with available denominator data from 2008 to 2015. Figure 2. Errors were categorized by site and by type: duplicate registration (multiple records existing for a single patient), doppelganger (confusion between records of two or more patients with similar identifiers), comingling (two or more patients using the same medical record file), missing patient armband, incorrect patient armband, name error (misspelled, missing, or incorrect), wrong date of birth, wrong sex, patients presenting another person's identification at registration, mistyping of medical record numbers, incorrect medical record numbers, errors in provincial health insurance numbers, and other errors. Numerical totals of errors at each site are given. Disclosures No relevant conflicts of interest to declare.