Laboratory diagnosis of peritonitis in patients treated with continuous ambulatory peritoneal dialysis.

Patients treated with continuous ambulatory peritoneal dialysis (CAPD) are constantly exposed to microbial invasion of the peritoneal cavity and rapid microbiological diagnosis of peritonitis is essential. Aseptic peritonitis is diagnosed in a high proportion of episodes when small volumes of dialysate are cultured. The aims of this study were to enumerate the microorganisms associated with clinical peritonitis and compare the efficacy of various culture systems for laboratory diagnosis of peritonitis. Four qualitative culture systems were compared: low (1 ml) volume and high (10 ml) volume inoculations of broth media, centrifugation (10 ml) followed by culture of the sediment and filtration (less than or equal to 100 ml) followed by culture of the filter. The pour plate and drop plate were the 2 quantitative methods used. Results of this study indicate that culture of 10 ml fluid volumes is comparable to culture of larger volumes sampled by filtration. Low volume cultures of fluid resulted in a lower proportion of positive cultures. The low numbers of viable microorganisms often found in dialysate from patients with peritonitis supports the concept of culturing a minimum of 10 ml of fluid.