Expression of cancer antigen 125 by peritoneal mesothelial cells is not influenced by duration of peritoneal dialysis

Objective: To investigate the presence of cancer antigen 125 (CA125) on mesothelial cells in the effluent of peritoneal dialysis (PD) patients and to analyze the effect of duration of PD on the number of mesothelial cells in peritoneal effluent, the number of CA125-positive cells, and dialysate CA125 concentration. Design: A cross-sectional study in which long-dwell peritoneal effluents were investigated for mesothelial cells and CA125. Setting: A university hospital population of chronic PD patients. Patients: 33 stable PD patients who were free of peritonitis during the investigation and during the 4 weeks prior to the study. Methods: Examination of cytospin preparations of peritoneal effluent stained with May-Grunwald Giemsa, and also with an immunocytochemical double-staining method consisting of anticalretinin (pan-mesothelial cell marker) and OC125. Results: A close relationship was present between the numbers of mesothelial cells counted with the two staining methods (r=0.998, p<0.001). On average, 92% of mesothelial cells were positive for CA125, ranging between 75% and 100% in 80% of the patients. Correlations were found between the effluent CA125 concentration and the total number of mesothelial cells (r=0.64, p<0.001), and also the number of CAI 25-positive cells (r=0.66, p<0.001). A negative effect of time was seen on the effluent CA125 concentration, the total number of mesothelial cells, and the number of CA125-positive mesothelial cells. However, no effect of time was present on the percentage CA125-positive cells. Conclusions: On average, 92% of mesothelial cells in peritoneal effluent are positive for CA125. This figure is not dependent on the duration of PD. Long-term PD is associated with low dialysate CA125 concentrations, a low number of mesothelial cells, and a low number of CA125-positive mesothelial cells in effluent. These results support the hypothesis that dialysate CA125 can be used as a marker of mesothelial cell mass in stable PD patients.