Certain embodiments disclosed herein are directed to methods and kits for detecting and quantifying in patient peritoneal fluid, such as spent peritoneal dialysis buffer, peptides having amino acid sequences related to megakaryocyte potentiating factor. The methods and kits can be used to monitor the biological status of the mesothelial lining of the peritoneal cavity in a patient, to predict development of a pathology of the mesothelium in an otherwise asymptomatic patient, and/or to assess the risk and suitability of a therapeutic method. In particular, the method can be used to assess negative effects of peritoneal dialysis on the biological integrity of the peritoneum, and thus to determine the time point when peritoneal dialysis treatment should be discontinued in favor of hemodialysis in a patient with kidney dysfunction, in order to avoid the development of peritoneal hypertrophy and other progressive mesothelial disorders such as encapsulating peritoneal sclerosis.