The purpose of the current diagnostic study is to show the diagnostic characteristics of serum interleukin-6 for the pre-operative diagnosis of PJI either as a single test or in combination of synovial IL-6 (sIL-6) and CRP (sCRP), to assess the optimal threshold value, and to compare these results with the currently available diagnostic standards. The gene discussed is IL6; the disease is juvenile polyposis syndrome.