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

• Neuraxial catheters improve postoperative pain but are contraindicated with anticoagulation.
• Subcutaneous unfractionated heparin prophylaxis may elevate aPTT.
• We examine aPTT values prior to and during prophylactic subcutaneous heparin therapy.
• Prophylactic subcutaneous heparin caused a small, but significant, increase in aPTT.

Study ObjectiveCharacterize the incidence of elevated aPTT results in patients treated with prophylactic, subcutaneous unfractionated heparin (UFH).DesignRetrospective, cohort analysis.SettingSingle-center, university hospital.MeasurementsEvaluation of 257 patients with activated partial thromboplastin time (aPTT) testing both prior to and following subcutaneous (SC) unfractionated heparin (UFH) therapy.Main ResultsEvaluated 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.ConclusionsTreatment with UFH resulted in a small, but significant, increase in aPTT.