A diagnostic method for the identification of a subject suffering from a primary non-infectious disease having an increased risk of an adverse outcome potentially being induced by the administration of an antibiotic to said subject comprising the determination of the level of Procalcitonin (PCT) or a fragment thereof or a precursor or fragment thereof having a length of at least 12 amino acid residues in a sample of a bodily fluid from said subject and the correlation of the determined level to a potential risk induced by the administration of an antibiotic, as well as a kit for performing the method and methods of treatment based thereon.