To increase the adhesion strength of coagulated blood on a surface by increasing the surface interaction of blood-inherent components like fibrin/fibrinogen and thrombocytes it is described to treat the surface by exposing it to ionized atoms or molecules. The surface treatment according to the invention is applied on plastic disposables used in blood diagnostics (e.g. hemostasis analysis) as well as medical implants like artery sealings. The improved blood clot adhesion results in higher diagnostic security due to reduced measurement failure (e.g., for patients with increased thrombocyte content) and in better significance of special tests (e.g., hyperfibrinolysis diagnosis).