The present invention relates to compositions and methods for detecting muscle atrophy in a subject. The invention also provides novel biomarkers that allow in vitro or ex vivo detection of muscle mass loss in a subject. The invention also relates to the use of muscle atrophy as an indicator of the occurrence, or the risk of occurrence of a disease or a disorder in a subject, including addressing the potential deleterious effect of some therapies and the effectiveness of potential countermeasures. Furthermore, the invention relates to kits and reagents, such as oligonucleotides, for use in these methods.