Laboratory diagnosis ofperitonitis inpatients undergoing continuous ambulatory peritoneal dialysis

SUMMARY A simple laboratory methodforculture ofcontinuous ambulatory peritoneal dialysis (CAPD)fluids isdescribed. Guidelines forantimicrobial therapy are discussed basedon results from18patients studied over an 11-week period. Cephalosporins appeared tobea rational choice fortherapy while awaiting laboratory results. Continuous ambulatory peritoneal dialysis (CAPD) hasrecently beenintroduced asanalternative to haemodialysis orperitioneal dialysis forpatients suffering fromchronic renal failure. Theadvantages ofthis procedure include thelack ofneedforspecial equipment inthehome, thefact that bagchanges can becarried outbythepatient without assistance, thelackofneedforvascular access, theincreased mobility resulting fromindependence ofadialysis centre andanincreased feeling ofwellbeing.' Howeverithasbeenfoundthata significant proportion ofpatients receiving this formofdialysis develop symptoms andsigns suggestive ofbacterial peritonitis.2 Conventional methodsofculture of peritoneal dialysate fromthese patients haveoften proved negative despite thepresence ofpuscells intheperitoneal fluid andclinical evidence of infection.3 In theory therearethreepossible explanations fornegative culture results. Firstly thecondition may be non-bacterial inorigin. Alternatively eveniftheinfection isbacterial the causative agents maynotbedetected bythemethods usedbecause their numbers aresmall orbecause their cultural requirements areexacting. Thethird possibility isthatbacteria maybeprevented from growing invitro bysubstances present inthe dialysate. Various workers haveattempted toimprove the rateofrecovery ofbacteria.24 Inonemethod100ml ofdialysate ispassed through a045,ummembrane filter-the filter isdivided andhalfcultured aerobically, theother half anaerobically onenriched solid media. Thedisadvantages ofmethods involving filtration oflarge volumes offluid include blockage of thefilter with cells andcontamination offilters during division andtransfer tosolid media. Another method involves inoculation of2mlofdialysate into nutrient brothand.chopped meat carbohydrate broth.