Incidence and risk factors for PTT prolongation in patients receiving low-dose unfractionated heparin thromboprophylaxis.

Low-dose unfractionated heparin (LDUH) prophylaxis decreases the incidence of venous thromboembolism (VTE) in hospitalized patients, but increases the risk of bleeding events. Patients who develop a prolonged activated partial thromboplastin time (aPTT) while on LDUH may be at higher risk for bleeding complications. To determine the incidence and risk factors for aPTT prolongation in hospitalized patients receiving LDUH thromboprophylaxis, we performed a retrospective pharmacoepidemiologic cohort study of adult patients admitted to an academic medical center from September 2013 through September 2015. Among 3857 patients with at least one aPTT checked within 24 h of LDUH administration, aPTT prolongation > 1.5 times the upper limit of normal occurred in 131 (3.4%). Age 68-78 years (OR 1.6, 95% CI 1.01-2.4), age > 78 years (OR 1.9, 95% CI 1.3-2.9), female gender (OR 1.9, 95% CI 1.4-2.5), black race (OR 1.6, 95% CI 1.1-2.3), low BMI (OR 1.8, 95% CI 1.3-2.5), being admitted to a surgical service (OR 0.5, 95% CI 0.3-0.8), and receipt of high-dose (> 10,000 units in a day) unfractionated heparin prophylaxis (OR 1.4, 95% CI 1.003-2.0), were independently associated with aPTT prolongation after LDUH exposure. LDUH VTE prophylaxis is associated with aPTT prolongation in 3.4% of general hospitalized patients. We demonstrated several factors independently associated with aPTT prolongation. Monitoring aPTT levels may be indicated for select patients on LDUH thromboprophylaxis who are at high risk or consequence of bleeding and for aPTT prolongation.