OBJECTIVE: To investigate the usefulness of dialysate IgG and C3 concentrations in predicting likelihood of developing peritonitis. DESIGN: Prospective, longitudinal, and comparative study. SETTING: Single university teaching hospital dialysis unit and outpatient clinic. PATIENTS: Thirty-four uremic patients were studied (20 males, 14 females: mean age 47.2, range 20-73 years). Monthly serum and overnight dialysate (eight- to eleven-hour dwell) samples were obtained for IgG and C3 estimations over the first six months of the study, and trimonthly samples were obtained thereafter. All patients performed exchanges using standard transfer sets (Baxter system II, Baxter Healthcare Ltd., Thetford, Norfolk, U.K.), used no hypertonic fluid (3.86%) for overnight exchanges, and were followed up for a minimum of 18 months. OUTCOME MEASURES: Dialysate and serum levels of IgG and C3; peritonitis episodes. RESULTS: Forty-five episodes of peritonitis occurred in 24 patients during the study period. We examined opsonin levels in the group as a whole, and then in two subgroups of patients: those who remained peritonitis-free throughout the study, and those who did not. There were no significant differences between IgG and C3 levels in the two groups at any time point, and large interpatient and intrapatient variation in levels were seen. CONCLUSION: Dialysate levels of IgG and C3 from the overnight dwell are not helpful in predicting the risk of developing continuous ambulatory peritoneal dialysis peritonitis in individual patients. No correlation was found between opsonin levels and onset of clinical peritonitis.

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