Early detection of peritonitis in continuous ambulatory peritoneal dialysis patients by use of chemiluminescence: evaluation of diagnostic accuracy by receiver-operating characteristic curve analysis.

Continuous ambulatory peritoneal dialysis (CAPD) is now a widely accepted treatment for end-stage renal disease. However, the high incidence of peritonitis is a major complication of CAPD. Polymorphonuclear leukocytes (PMNs) play a major role in antimicrobial response of the host. During phagocytosis, the PMNs undergo a striking increase in oxidative metabolism, known as the respiratory burst, and emit light as chemiluminescence (CL). CL is thus a sensitive measure of PMN oxidative potential and correlates well with antimicrobial activity. In view of the observation of increased susceptibility to infection in CAPD patients, we have studied lucigenin- and luminol-enhanced CL in peritoneal fluids of these patients and assessed the diagnostic accuracy of these tests by ROC curve analysis. ROC curves showed diagnostic accuracies for both tests that were superior to counts of PMNs in the dialysis fluid (P <0.001). At selected cutoff values of 150000 cpm/vial for lucigenin CL and 600000 cpm/vial for luminol CL, sensitivities were 100%. Specificities for lucigenin and luminol CL were 89% and 80%, respectively. Our results suggest that CL measurements can be used as an early marker for the presence of infection in CAPD patients.

The role of free prostate-specific antigen in the diagnosis of prostate cancer.

OBJECTIVE: To determine whether the free/total prostate-specific antigen (PSA) ratio can discriminate between patients with prostate cancer or benign prostatic hyperplasia (BPH). PATIENTS AND METHODS: A prospective study was conducted using free and total PSA assays in patients who underwent transrectal-ultrasound guided biopsies indicated by a total serum PSA level of > 4 ng/mL and/or a positive digital rectal examination. Sixty-nine men (median age 68 years, range 57-86) who presented to our out-patient department with symptoms of prostatism were included in the study. Blood samples were drawn from all patients before biopsy. RESULTS: Histopathological examination detected prostate cancer in 17 of 69 (25%) patients and 13 of these 17 patients had a free/total PSA ratio of < 0.15; only 12 of 52 (23%) patients with BPH had a ratio of < 0.15. Receiver operating characteristic analysis indicated a threshold free/total PSA ratio of < or = 0.15 was the optimum discriminatory level. In the whole study group, this threshold had sensitivity, specificity, positive- and negative-predictive values of 76%, 77%, 52% and 91%, respectively. There were 40 patients with serum PSA levels of 4-10 ng/mL and 17.5% (7/40) of these were diagnosed with cancer. Using a free/total PSA ratio of 0.15 would have failed to diagnose two patients of seven with prostate cancer but 30 patients would have avoided a biopsy. In this subgroup, the threshold ratio of 0.15 had sensitivity, specificity, positive- and negative-predictive values of 71%, 85%, 50% and 93%, respectively. The rates for a PSA density (PSAD) at a threshold of > or = 0.15 were 71%, 76%, 38%, 93%, respectively. CONCLUSION: These results indicate that using the free/total PSA ratio gives a significant improvement over PSAD and total PSA values alone in the diagnosis of prostate cancer: its use may also enhance the diagnostic accuracy in patients with intermediate PSA levels.