Limulus amoebocyte lysate assay in the diagnosis of peritonitis in patients receiving continuous ambulatory peritoneal dialysis.
OBJECTIVE
To evaluate the Limulus amoebocyte lysate (LAL) assay for differentiating Gram positive from Gram negative peritonitis in patients receiving continuous ambulatory peritoneal dialysis (CAPD).


METHODS
One hundred and six patients with suspected peritonitis were studied. LAL assay was performed by adding 0.1 ml of CAPD fluid to 0.1 ml of LAL reagent and incubating in a heating block for 60 minutes at 37 degrees C. The sensitivity of the reaction was determined by: (i) diluting endotoxin in distilled water and used (filter sterilised) peritoneal dialysis fluid; and (ii) diluting a broth culture of E coli used in peritoneal dialysis fluid. A positive LAL assay was defined as the constant stability of the clot through an inversion of 180 degrees.


RESULTS
Compared with bacterial culture, the LAL assay had a sensitivity of 65% and a specificity of 98%. The sensitivity of microscopy compared with culture of Gram negative organisms was 76%; overall sensitivity of microscopy in comparison was 80%.


CONCLUSIONS
The Gram stain was more sensitive than has previously been reported; the LAL assay was specific but insensitive for the diagnosis of CAPD peritonitis. There was a correlation between reduced leucocyte count and culture; this was reduced in cases from which Gram negative organisms had been isolated. It is recommended that laboratories evaluate their Gram stain procedure to improve its sensitivity because the LAL assay is not a satisfactory substitute.
Department of Microbiology, University of Western Australia, Nedlands.
R A
RA
Bowman
A S
AS
Medley
K T
KT
Karthigasu
D003937:Diagnosis, Differential; D005840:Gentian Violet; D016905:Gram-Negative Bacterial Infections / Q000175:diagnosis* / Q000209:etiology; D016908:Gram-Positive Bacterial Infections / Q000175:diagnosis* / Q000209:etiology; D006801:Humans; D008033:Limulus Test; D010531:Peritoneal Dialysis, Continuous Ambulatory / Q000009:adverse effects*; D010538:Peritonitis / Q000175:diagnosis* / Q000382:microbiology; D010619:Phenazines; D012680:Sensitivity and Specificity; D013194:Staining and Labeling
C035863:Gram's stain; D010619:Phenazines; D005840:Gentian Violet