Effect of Subcutaneous Unfractionated Heparin Prophylaxis on Activated Partial Thromboplastin Time: A Retrospective Evaluation

Abstract Study Objective Characterize the incidence of elevated aPTT results in patients treated with prophylactic, subcutaneous unfractionated heparin (UFH). Design Retrospective, cohort analysis. Setting Single-center, university hospital. Measurements Evaluation of 257 patients with activated partial thromboplastin time (aPTT) testing both prior to and following subcutaneous (SC) unfractionated heparin (UFH) therapy. Main Results Evaluated patients received UFH 5000 units every 8 hours. Baseline aPTT values were within the normal range (mean ± SD, 32.0 ± 8.5 seconds). After initiation of UFH, aPTT values increased (mean ± SD, 37.6 ± 15.2 seconds). After 24 hours of SC UFH, mean aPTT values (mean ± SD, 38.6 ± 15.5) exceeded the normal laboratory range (23.3–35.7 seconds). An elevated aPTT result after UFH was associated with baseline aPTT, length of therapy, and weight-based UFH dose. A significant association was not identified between aPTT elevation and age, race, sex, history of liver disease, type of admission, or transfusion of blood products. Conclusions Treatment with UFH resulted in a small, but significant, increase in aPTT.