The present invention relates to a method of analyzing a blood sample of a subject for the presence of a disease marker, said method comprising the steps of a) extracting nucleic acid from anucleated blood cells in said blood sample to provide an anucleated blood cells-extracted nucleic acid fraction, and b) analyzing said anucleated blood cells-extracted nucleic acid fraction for the presence of a disease marker, wherein said disease marker is a disease-specific mutation in a gene of a cell of said subject, or wherein said disease marker is a disease-specific expression profile of genes of a cell of said subject.