The present invention relates to methods and compositions for diagnosis of inflammatory disorders, and in non-limiting embodiments, of inflammatory disorders associated with elevated interleukin-1β (“IL-1β”), based on increased levels of follistatin-like protein 1 (“FSTL-1”). In particular non-limiting embodiments, the invention further provides for methods of identifying subjects with systemic onset juvenile idiopathic arthritis (“SOJIA”) who are at increased risk for developing macrophage activation syndrome (“MAS”) comprising detecting, in said subjects, hyper-increased levels of FSTL-1. In additional non-limiting embodiments, the invention provides for methods of identifying subjects with Kawasaki disease who are at increased risk of developing aortic aneurysms comprising detecting, in said subjects, hyper-increased levels of FSTL-1.