Testing of coagulation induced by external communicating medical devices is an International Standardisation Organization (ISO) requirement for products exposed to human blood. Four categories of tests are indicated by ISO 10993/4: a clotting test (partial thromboplastin time; PTT), thrombin generation, fibrinogen deposition, or measurement of coagulation split products. We evaluated the specificity of these tests on various polymers and found only thrombin generation and fibrinogen binding sensitive and reproducible tests while thrombin generation correlated best with the classical PTT. The thrombin generation assay is therefore the method of choice for testing coagulation induced by biomaterials and medical devices.