The invention relates to measuring of the adhesion of platelets ex vivo. In this method, monodisperse polymer particles are added to blood, and the number of platelets in the blood are measured before and after shaking of the sample. The level of adhesion of the platelets is determined by comparing the number of platelets prior to shaking with the number of platelets after shaking. Methods of establishing an adhesion index and diagnosis of a patient are also provided.