Biocompatibility of extracorporeal blood treatment. Selection of haemostatic parameters.

Since thrombogenesis is a multifactorial process, assessment of the thrombogenic property (thrombogenicity) of a material or device in contact with circulating blood requires the consideration of a number of pathways and their extent as well as time course of activation. The processes to be considered are: (a) thrombosis, (b) activation of the blood coagulation system, and (c) activation of blood platelets. The clinical relevance of testing the thrombogenicity on the basis of these three categories largely depends on the experimental conditions of the test model. Only test models that simulate the conditions of a device during use may predict accurately the thrombogenicity of a material or device during clinical application. Regarding the test category of thrombosis a visual inspection of the device (clotting within the device) is highly relevant but difficult to standardize. Microscopic analysis, either by light-microscopy or scanning electron-microscopy, of the surface of the material or device after its removal from the in-use position is of great importance in evaluating the biological response of the material to blood. For the test categories of blood coagulation and platelets, a rather large number of standardized ready-to-use kits are commercially available. In spite of their aforementioned limitations the assays listed in Table 2 are recommended for their use in assessing thrombogenicity. Because an adequate heparin treatment will mask the intrinsic thrombogenicity of a material or device, monitoring heparin treatment is strongly recommended. If heparin levels have to be measured in whole blood, a clotting assay like the Heptest is recommended.(ABSTRACT TRUNCATED AT 250 WORDS)