Recent data have suggested that standard unfractionated heparin (UFH) protocols may over-anticoagulate obese patients. The goal of this retrospective study was to observe differences in anticoagulation parameters and safety outcomes for standardized antifactor Xa UFH protocols in obese and non-obese populations. Obese patients (N = 148) were identified over a 20-month period and matched to 148 non-obese patients based on age, gender, and admission date. Patients were included if they were on one of three approved UFH protocols [high (target antifactor Xa 0.3-0.7 IU/mL), moderate (0.3-0.5 IU/mL), or low (0.1-0.2 IU/mL) dose] for ≥24 consecutive hours and had ≥1 antifactor Xa level drawn during the infusion. Groups were compared for doses at first and second consecutive therapeutic antifactor Xa level, major bleeding, and in-hospital mortality. Obese patients required a significantly lower mean weight-based infusion rate to attain first therapeutic antifactor Xa level compared to non-obese patients in both the high dose (19.45 vs. 15.29 units/kg/h, p < 0.001) and the moderate dose populations (15.0 vs. 12.94 units/kg/h, p = 0.003). Similarly, patients in both the high and moderate dose populations had significant differences in mean infusion rates to attain second consecutive therapeutic antifactor Xa levels. There was no difference between infusion rates for the primary outcomes in the low dose population. There was no difference between groups in major bleeding or mortality outcomes. Similar to data using UFH protocols based on activated partial thromboplastin time, obese patients require lower weight-based UFH doses to attain therapeutic anticoagulation. Institutions using or changing to antifactor Xa based protocols may need to modify protocols for obese patients.
Keywords: Anticoagulation; Antifactor Xa; Body mass index; Heparin; Obesity; Patient safety.