Real-time surveillance of gene expression of monocytes and lymphocytes obtained from a patient enables the detection of immune-response signal changes that are caused by (i) intrinsic inter-individual variability, e.g. gender, genetic/ethnic background, (ii) epigenetic age-related and temporal variations, (iii) extrinsic intra-individual extracellular ‘milieu’ stimuli, e.g. food and drink intake both long-term and immediately prior to blood draw, smoking, recent vaccination, … (iv) specific diseases that the blood test aims to detect, e.g. prostate cancer, lung cancer, and pancreatic cancer, and (v) other diseases/conditions unrelated to the disease, e.g. arthritis, acute infection, … which are not part of the target disease panel. Since extracellular vesicles, apoptotic CTCs, and related cellular debris such as apoptotic bodies, exosomes, and nucleosomes are cleared from circulation by professional phagocytic cells, this process leads to the acquisition of disease-specific (epi)genomic signatures in these phagocytic cells and their absence in non-phagocytic cells.