Exploration of appropriate anticoagulant reagents and reliability of porcine blood for in vitro evaluation of thrombogenicity

Background: A validated in vitro testing system is crucial to evaluate the thrombogenicity of new medical devices such as heart valve prostheses, since thromboses and thromboembolisms remain limiting factors in clinical application. The testing fluid, animal species, and anticoagulants may affect preclinical analyses. Our study aimed to investigate the use of unfractionated heparin (UFH) and low-molecular-weight heparin (LMWH) in reference to blood anticoagulation by citrate using porcine blood to determine their applicability in preclinical thrombogenicity testing. Methods: In a static experimental setting, material specimens of glass and polymethylmethacrylate were used to simulate different degrees of clotting activation. The specimens were exposed to porcine blood anticoagulated by either citrate, UFH or LMWH. Porcine blood obtained from the abattoir was compared with blood obtained from laboratory swine. Monitoring included complete blood count, activated partial thromboplastin time (aPTT), prothrombin time (PT), and fibrinogen time. Results: UFH-anticoagulated blood showed significant decreases in aPTT, PT, and thrombocyte count, most notably after glass-induced, strong activation of clotting. Blood anticoagulated with LMWH showed significant decreases in aPTT, PT and thrombocytes as well, but no significant differences between the effects of different clotting-activating materials were recorded. No relevant changes were observed with the use of citrate. Abattoir-derived blood had huge variability in baseline values; for example, thrombocyte count showed a 25.85% standard deviation from the mean value in citrated blood, 15.54% in UFH-anticoagulated blood, and 21.69% in LMWH-anticoagulated blood, whereas laboratory-derived blood varied only around 2.01%. Conclusions: We demonstrated the applicability of porcine blood in thrombogenicity testing. Special caution is required to standardize blood withdrawal methods and eliminate preanalytical interference. No distinct advantage of either type of heparin was detected