Abstract: The invention relates to a method for characterizing, in particular for quantifying molecular marker(s) that are intracellularly absorbed from tissues by blood macrophages that are recirculated from the tissues into the circulatory system, wherein the following steps are carried out: application of an agent to whole blood, said agent inhibiting coagulation and/or agglomeration of whole blood; selecting and/or enriching and/or separating blood macrophages or leukocyte populations that contain blood macrophages from whole blood; perforating and/or lysing the selected blood macrophages or leukocyte populations containing the blood macrophages, optionally after previous permeabilization thereof; qualitatively and quantitatively determining non blood macrophage markers, namely molecular markers arising from tissue, after previously perforating and/or lysing the blood macrophages or leukocyte populations containing the blood macrophages, and an apparatus for carrying out the method.