Laboratory indices of clinical peritonitis: total leukocyte count, microscopy, and microbiologic culture of peritoneal dialysis effluent

Abstract

Total leukocyte count, microscopy, and conventional bacteriologic culture (10-ml sediment) of dialysis effluent were assessed for their ability to detect peritonitis in patients on peritoneal dialysis. A total of 73 patients were surveyed over a 17-month period. Laboratory findings included an examination of 1,774 dialysate samples and culture results from blood, wounds, indwelling catheters, and other specimens. Of 90 peritonitis events, 72 were culture positive. Gram-stained films were positive in no more than 14% of the dialysates collected during periods of clinical peritonitis. Factors which adversely affected the microscopic or cultural detection of microorganisms in effluent included the concentration of organisms in dialysate, antibiotic therapy, and growth medium used. Seeding of the peritoneum with organisms originating from other sites of infection or colonization was documented, although infrequent, yet bacteremia secondary to peritonitis was not seen. Because of the frequent isolation of microorganisms from dialysates in the absence of clinical peritonitis, culture-positive findings were a poor predictor of peritonitis without other evidence of infection. Detection of peritonitis by total leukocyte count (without a differential count) of dialysate specimens was adversely affected by the overlap in cell counts between dialysates collected either during or in the absence of peritonitis. This was attributed in part to nonspecific increases in dialysate cell count in the absence of peritonitis and was associated with intermittent dialysis and extraperitoneal infection.

Microbiological aspects of peritonitis associated with continuous ambulatory peritoneal dialysis.

“…In one study of 3,876 daily surveillance cultures of dialysates, 183 positive cultures were detected, but only 30 of them were associated with peritonitis (as defined by cloudy fluid plus abdominal pain); the other 153 did not indicate present or future infection (152). Other authors (29,31,89,116) also found growth in up to 10% of effluents from nonperitonitis patients. In such cultures, coagulase-negative staphylococci, Propionibacterium, Acinetobacter, and Bacillus species (130,152), and (rarely) agents known to cause more severe forms of CAPD peritonitis (116,152) were found.…”

“…Gram-positive organisms may have a higher chance of being detected on Gram stain than gram-negative ones (82). Positivity rates of Gram stains increase with the cellularity of the effluent (90) and decreases after the initiation of antimicrobial therapy (89).…”

“…Cultures of fluids from patients with CAPD peritonitis have been reported as negative in 4 to 48% of all episodes (31,73,89,123,124,139,148). Such results are significantly more frequent when WBC counts are below 500/mm3 (36,90).…”

A peritoneal dialysis patient with fatal culture‐negative peritonitis

“…1 Approximately 90% of patients with true infective peritonitis will have dialysate white cell counts greater than 100 × 10 6 /L, while 85% of non-infected patients will have counts below this figure. 2,3 The percentage of neutrophils in a differential white cell count was >50%, and this seems to be an even more sensitive indicator of peritonitis than the absolute cell count. 4,5 Non-peritonitic fluids mostly demonstrate mononuclear cells, while infected fluids (including those caused by fungi and mycobacteria) generally show a predominance of polymorphonuclear leucocytes.…”

“…It is important to avoid dismissing such growths as contaminants, as the falsepositive rate for dialysate cultures is low (<10%) and is considerably lower if fungi are isolated. 3 Interestingly, positive initial dialysate cultures were repeated in approximately one-third of all reported cases of fungal peritonitis, presumably because of doubts about the pathogenicity of the isolated fungus. Nevertheless, in this patient, the isolated yeast was probably a contaminant in view of the delayed scanty growth of multiple organisms, which were not subsequently isolated on repeat cultures.…”