The invention relates to a novel diagnostic marker CT-proADM (C-terminal fragment of preproADM, SEQ ID No, 1) for diagnosing and/or stratifying the risk of diseases. Also disclosed is a method for diagnosing and/or stratifying the risk of diseases, particularly cardiovascular diseases, cardiac insufficiency, and infections and/or inflammations of the lungs and respiratory tract. In said method, the CT-proADM (SEQ ID No. 1) marker, or a partial peptide of fragment thereof, or said marker contained in a marker combination (panel, cluster) is determined in a patient who is to be examined. The invention further relates to a diagnostic apparatus as well as a kit for carrying out said method.