Objectives: Preoperative testing for carotid endarterectomy (CEA) often includes blood 3 typing and antibody screen (T&S). In our institutional experience, however, transfusion 4 for CEA is rare. We assessed transfusion rate and risk factors in a national clinical 5 database to identify a cohort of patients in whom T&S can safely be avoided with the 6 potential for substantial cost savings. 7 Methods: Using the NSQIP database, transfusion events and timing were established for 8 all elective CEAs in 2012-13. Comorbidities and other characteristics were compared for 9 patients receiving intra- or postoperative transfusion and those that did not. After random 10 assignment of the total data to either a training or validation set, a prediction model for 11 transfusion risk was created and subsequently validated. 12 Results: Of 16,043 patients undergoing CEA in 2012-13, 276 received at least one 13 transfusion prior to discharge (1.7%). 42% of transfusions occurred on the day of surgery. 14 Preoperative hematocrit < 30% (Odds ration OR: 57.4; 95% confidence interval CI: 29.6- 15 111.1), history of congestive heart failure (OR: 2.8; 95%CI: 1.1 – 7.1), dependent 16 functional status (OR: 2.7; 95%CI: 1.5-5.1), coagulopathy (OR: 2.5; 95%CI: 1.7-3.6), 17 creatinine ≥ 1.2 mg/dl (OR: 2.3; 95%CI: 1.6-3.3) preoperative dyspnea (OR: 2.0; 95%CI: 18 1.4-3.1) and female gender (OR: 1.6; 95%CI: 1.1-2.3) predicted transfusion. A risk 19 prediction model based on these data produced a C-statistic of 0.85; application of this 20 model to the validation set demonstrated a C-statistic of 0.81. 93% of patients in the 21 validation set received a score of 6 or less corresponding to an individual predicted 22 transfusion risk of 5% or less. Omitting a T&S in these patients would generate a 23 substantial annual cost saving for NSQIP hospitals.