The anticoagulant capacity of plasmatic unfractionated heparin decreases at 23°C

Abstract

Unfractionated heparin (UFH) and low-molecular-weight heparin (LMWH) are important clinical anticoagulants. As polynegative molecules they are potential triggers of the contact phase of coagulation. An incubation temperature lower than the physiological 37 degrees C favours intrinsic haemostasis activation by the polynegative molecule SiO2. The efficiency of UFH and LMWH after a plasmatic preincubation at 37 or at 23 degrees C is therefore studied. Samples (150 mul) of unfrozen pooled normal plasma supplemented with 0, 0.01, 0.1, or 1 IU/ml heparin or dalteparin in 5-ml polystyrole tubes were incubated for 10-70 min at 37 or at 23 degrees C. The extrinsic coagulation activity assay (EXCA) was then performed. Preincubation at 37 degrees C of 0.1 IU/ml plasmatic UFH does not result in any thrombin generation in EXCA-1, whereas preincubation at 23 degrees C results in a thrombin generation of about 0.1 IU/ml thrombin. Plasmatic UFH (0.01 IU/ml) at 23 degrees C acts nearly half as efficiently as 0.01 IU/ml plasmatic LMWH. Polynegatively charged niches particularly in the larger UFH molecule might trigger the contact system of haemostasis, especially at 23 degrees C. In contrast, the anticoagulant capacity of LMWH does not change significantly with temperature.