Sensitivity evaluation of the Gen-Probe AMP-CT assay by pooling urine samples for the screening of Chlamydia trachomatis urogenital infection

The sensitivity of two urine pool sizes versus individual testing, to detect Chlamydia trachomatis urogenital infection, was evaluated using the Gen-Probe AMP-CT assay. Thirty-three (33) known polymerase chain reaction (PCR) positive urine specimens were combined with 231 fresh first-catch urine (FCU) samples in 33 groups of four and 33 groups of eight, to make up 4X and 8X pooled samples, respectively. Gen-Probe AMP-CT assay was performed on pools as well as on individual samples at the same time. For the discrepant cases, the known positive samples were diluted 1:4 and 1:8 using the manufacturer's dilution buffer and were retested. Additional positive specimens found among fresh FCU samples were also tested by the Amplicor-PCR assay to confirm their positivity. The sensitivities of 8X pooling, 4X pooling and individual testing were 86.5%, 94.3% and 91.9%, respectively. The Gen-Probe AMP-CT assay applied to a 4X urine pooling model was highly sensitive and may be useful for a population based screening programme.

Preventing ascorbate interference in ion-chromatographic determinations of urinary oxalate: four methods compared

In an attempt to decrease ascorbate interference on the ion-chromatographic determination of urinary oxalate, we compared the effectiveness of four different methods for ascorbate elimination by analyzing a representative urine pool supplemented with successive ascorbate additions. Two of the methods--treatment with ferric ions or boric acid--have been described elsewhere; treatments with nitrites or ascorbate oxidase (EC 1.10.3.3) are investigated here as possible alternatives. Consideration of the main features, advantages, and drawbacks of the four procedures leads us to conclude that boric acid dilution is a good routine method and that pre-incubation with ascorbate oxidase reliably prevents ascorbate interference in assays of urinary oxalate.

Extending the detection limit of the TDx fluorescence polarization immunoassay for benzoylecgonine in urine.

This modified calibration method decreases from 300 to 27 micrograms/L the limit of detection for the cocaine metabolite (hydrolysis product), benzoylecgonine, by the Abbott Laboratories TDx fluorescence polarization immunoassay. For this determination we used 30 controls prepared from a single urine pool known to be negative for cocaine metabolite. Assay of 80 controls prepared from 20 different patients' urine samples yielded a limit of detection of 44 micrograms/L. To test these limits of detection, we analyzed 90 patients' urine samples known to be negative for cocaine metabolite and 74 patients' samples known to be positive for cocaine metabolite, using the TDx with our revised calibration. Results for two of the known negative samples and 96% of the samples containing cocaine in the 50 to 100 micrograms/L range fell above the 44 micrograms/L limit. The TDx showed excellent calibration stability. For 28 days during the test, the instrument was not recalibrated. During this period the day-to-day analysis of 50 micrograms/L controls produced a mean TDx response of 0.485 (SD 0.007) with a coefficient of variation of 1.5%.

Proteinuria after Burn Injury

Qualitative and quantitative aspects of the excretion of protein after burn injury have been investigated. The excretion of total protein and of albumin have been measured nephelometrically while the excretion of proteins of both serum and non-serum origin have been measured by immunoelectrophoresis using antiserum against serum proteins or against a pool of urine from burned patients. Comparison of the patterns of proteins observed in urine using these two different antisera showed the presence of at least three major proteins that did not originate from the plasma. The excretion of two of these three proteins followed closely the pattern of total protein excretion which reached a maximum at five to seven days after injury. The excretion of albumin was greatest in the first 48 hours after injury. Examination of the original burn patients' urine antigen by sodium dodecyl sulphate polyacrylamide gel electrophoresis showed that this urine pool contained greater amounts of lower molecular weight proteins than were observed in a pool of normal urines. The observations suggest that a biphasic renal pathophysiology is observed after burn injury. Initially, there develops a mild transient glomerular lesion which progresses to a different state which shows at least some of the features of a tubular proteinuria.