Title: Fructosamine as a Predictor of Adverse Post-Operative Outcomes in Total Shoulder Arthroplasty Patients Background: Serum fructosamine has been shown to be a significant predictor of post-operative adverse outcomes in joint replacement patients. Fructosamine is a measure of blood sugar over a shorter time period of 14 to 21 days, making it a more useful marker of blood sugar control pre-operatively. The objective is to assess adverse post-operative outcomes after both anatomic and reverse total shoulder arthroplasty (TSA) in relation to fructosamine, HbA1c, and blood glucose. Methods: This prospective cohort study includes patients undergoing TSA from multiple providers. Pre-operative data was collected that includes demographics, diabetic status, insulin dependence, Visual Analog Scale (VAS), Range of Motion data (ROM), PROMIS surveys, and patient fructosamine, HbA1c, and fasting blood glucose levels. Follow-up data was obtained at 6 weeks and 3 months post-operatively. This included data for superficial infection, deep infection, medical complications, emergency room visits, hospital readmissions, reoperations, VAS scores, and updated ROM. Results: A total of 101 patients were recruited for the study, comprised of 44 males and 57 females. Mean age was 68.5, ranging from 34 to 90 years. Of the total, 25 patients had a pre-operative diagnosis of diabetes. None of these patients experienced medical complications, superficial infections, deep infections, hospital readmissions, or reoperations. A total of 7 patients experienced medical complications with only 2 having reoperation. Only 1 of these patients that reoperated had elevated fructosamine (>292 µmol cut-off) and an elevated HbA1c (>6.5% cut-off). The average fructosamine was 221.8 µmol, with a range from 106.6 µmol to 404.2 µmol. The average HbA1c was 5.8, with a range from 3.4 to 8.7. Blood glucose and HbA1c showed no significant relationship with any of the tested variables. Elevated fructosamine showed a positive association with a decreased active external rotation (ER) (p=0.01) which is lost at the 3-month follow-up post-operatively (p=0.59). No other significance was found with VAS, ROM, or PROMIS through 3 months post-operatively. Conclusions: Preliminary data analysis suggests that fructosamine, HbA1c, and blood glucose are not reliable predictors of post-operative outcomes. The only significant outcome was decreased active ER with higher levels of fructosamine 6 weeks post-operatively. No significant determination can be made at this time as the study is actively recruiting patients to increase study power.