Limulus amoebocyte lysate (LAL) assay and rapid detection of gram negative bacterial peritonitis in patients receiving CAPD

Diagnostic Value of Effluent Endotoxin Level in Gram-Negative Peritonitis in Capd Patients

Objective

To evaluate the diagnostic usefulness of effluent endotoxin by Limulus amoebocyte lysate (LAL) assay in gram-negative peritonitis patients on continuous ambulatory peritoneal dialysis (CAPD) therapy.

Design

Prospective study with patients serving as their own controls. Standard microbiologic work up and endotoxin analysis of effluents (night dwell) were done during the pre- and posttreatment phases.

Setting

Specimens from three teaching hospitals were processed and tested at a common center. Patients were left for treatment at their respective centers without intervention.

Patients

32 clinical peritonitis and 40 infection-free CAPD patients were studied.

Results

75% ( n = 24) of cultures were positive: 41.6% ( n = 10) gram-negative and 58.4% ( n = 14) gram-positive bacteria. Effluents of pre- and posttreated gram-negative cultures had endotoxin levels of 1.53 ± 0.169 and 0.214 ± 0.085 endotoxin units (EU)/mL, respectively ( p < 0.0001); pre- and posttreated gram-positive levels of 0.102 ± 0.06 and 0.122 ± 0.052 EU/mL, respectively ( p > 0.05); pre- and posttreated culture-negative peritonitis levels of 0.110 ± 0.025 and 0.087 ± 0.031 EU/mL, respectively ( p > 0.05); peritonitis-free effluents contained 0.117 ± 0.079 EU/mL. The diagnostic specificity and the sensitivity of LAL assay were 100% and 98.2% respectively.

Conclusion

Where initial microbiological work-up cannot demonstrate a pathogen, effluent endotoxin determined by quantitative LAL assay is a useful marker for diagnosis and management, within safe time limits, of gram-negative peritonitis in CAPD patients.

Gel clot LAL assay in the initial management of peritoneal dialysis patients with peritonitis: a retrospective study

BACKGROUND

Indiscriminate use of broad-spectrum antibiotic treatment of peritonitis in peritoneal dialysis patients may have either unwanted side-effects or contribute to the development of antibiotic resistance. This may be avoided by improved diagnosis at presentation. The Limulus amoebocyte lysate assay is a convenient test detecting bacterial endotoxins or fungal beta glucans. This study evaluates a qualitative Limulus amoebocyte lysate test as a diagnostic tool used at presentation of a peritoneal dialysis patient with peritonitis.

METHODS

One-hundred and eleven episodes of peritonitis in peritoneal dialysis patients have been analysed retrospectively. Limulus amoebocyte lysate results at presentation were compared with culture results. A Limulus amoebocyte lysate assay was performed using a commercial kit by incubating a mixture of dialysate effluent and Limulus amoebocyte lysate reagent at 37 degrees C. The development of a stable solid clot was considered positive. The specificity and sensitivity of the test were calculated.

RESULTS

The specificity of the Limulus amoebocyte lysate assay was found to be 98% and the sensitivity 74%. Limulus amoebocyte lysate assay was false-negative in 13 cases of Gram-negative peritonitis (22%). Limulus amoebocyte lysate was positive in three of seven cases of fungal peritonitis. The study included one case each with false-positive Limulus amoebocyte lysate and with culture-negative peritonitis.

CONCLUSIONS

The Limulus amoebocyte lysate assay is a convenient and valuable diagnostic tool for excluding Gram-positive peritonitis in peritoneal dialysis patients. This allows more specific antibiotic treatment at presentation and may avoid the development of bacterial resistance. A negative Limulus amoebocyte lysate test is not reliable for the exclusion of Gram-negative peritonitis. In the absence of a positive culture result 48 h after presentation, accompanied by a delayed response to treatment, a positive Limulus amoebocyte lysate assay may indicate the presence of fungus. This justifies early empiric antifungal treatment before definitive culture results are made available. Routine Limulus amoebocyte lysate assay of dialysate effluent from continuous ambulatory peritoneal dialysis patients presenting with peritonitis is recommended.

Limulus amoebocyte lysate assay in the diagnosis of peritonitis in patients receiving continuous ambulatory peritoneal dialysis

AIMS

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.