The invention provides, in certain embodiments, a method of preventing and/or treating peritoneal injury and/or diminished function by administering an effective amount of one or more inhibitors of JAK. The invention also provides a pharmaceutical composition including a JAK inhibitor for the treatment of peritoneal injury and/or diminished function. In another aspect, the invention provides a method of detecting an indicator of peritoneal injury. The method entails assaying a biological sample for periostin, wherein the presence of periostin at an elevated level indicates the presence and/or degree of peritoneal injury. Also provided, are methods of identifying subject for treatment of peritoneal injury and/or diminished function, methods of determining progression of these conditions, as well as methods of determining subjects' response to treatment.