Nucleic acid amplification tests such as the BDProbeTec ET (BDPT) system are more prone to reproducibility problems than are antigen detection tests and culture. A repeat testing algorithm for all samples with method other than acceleration (MOTA) scores greater than or equal to the cutoff value (2,000) was developed for the BDPT system and applied in a clinical laboratory setting. All positive samples were retested, and if the result of the second test was below the cutoff value, a third test was performed to resolve the discrepancy. Nucleic acid amplification tests (NAATs) offer several advantages over culture and other methods for the detection of Chlamydia trachomatis and Neisseria gonorrhoeae in clinical specimens. These advantages include increased sensitivity, high throughput, no requirement for viable organisms, and the use of urine as an alternative to more difficult-to-obtain specimens. Disadvantages of NAATs include high cost, false-negative results due to the presence of amplification inhibitors in specimens, and false-positive results due to specimen crosscontamination.The BDProbeTec ET (BDPT) system (Becton Dickinson and Company, Franklin Lakes, N.J.) uses strand displacement amplification and fluorescent resonance energy transfer probes to simultaneously amplify and detect the DNAs of C. trachomatis and N. gonorrhoeae. The amplification targets are DNA sequences in the cryptic plasmid of C. trachomatis and in the pilin gene-inverting protein homologue of N. gonorrhoeae (4). A recent multicenter evaluation of the BDPT system demonstrated that it has sensitivity superior to that of chlamydia culture and performance characteristics similar to those of other commercially available NAATs for these organisms (7). According to a recent College of American Pathologists survey (2003 HC6-A), the BDPT system was the most common NAAT used by participants for detection of C. trachomatis and N. gonorrhoeae.NAATs are more prone than other tests to false-positive results due to specimen cross-contamination. False-positive test results are particularly problematic in low-prevalence patient populations, in which the impact on the positive predictive value of the tests is greatest. However, regardless of the population or health care setting, false-positive results for C. trachomatis and N. gonorrhoeae can have adverse medical, social, and psychological impacts on patients.The Centers for Disease Control and Prevention has recently issued guidelines for the selection, use, and interpretation of screening tests to detect C. trachomatis and N. gonorrhoeae infections (2). These guidelines suggest several approaches by which to detect false-positive test results. The approaches include (i) testing of a second specimen with a different test that uses a different target, antigen, or phenotype and a different format; (ii) testing of the original specimen with a different test that uses a different target, antigen, or phenotype and a different format; (iii) repetition of the original test of the original specimen with a blo...

Background-Platelet storage adversely affects platelet structure and function in vitro, and is associated with decreased platelet recovery and function in vivo. In pediatric transfusion medicine, it is not uncommon for small residual volumes to remain in parent units following aliquot preparation of leukoreduced apheresis-derived platelets (LR-ADP). However, limited data exists regarding the impact of storage on residual small volume LR-ADP.

We compared the performance of a laboratory-developed 5'-nuclease real-time polymerase chain reaction assay and a commercial assay (LightCycler, Roche Diagnostics, Indianapolis, IN) for quantification of Epstein-Barr virus (EBV) DNA. Using standards provided by the manufacturer, the LightCycler assay was linear from 100 to 1 million copies per reaction. Based on dilution of a plasmid containing the amplicon, the laboratory-developed assay was linear from 22 to 45 million copies per reaction. Both assays detected 0.5 copies of genomic EBV DNA per reaction; both showed good reproducibility with coefficients of variation from 0.3% to 2.4% for the LightCycler and 1.8% to 5.1% for the laboratory-developed assay. For 31 whole blood specimens with measurable values in both assays, the viral load values obtained with the LightCycler averaged 2.3-fold higher than those obtained with the laboratory-developed assay. Testing 30 matched whole blood and plasma samples in the laboratory-developed assay showed whole blood viral load values averaged 10-fold higher than those for plasma. The LightCycler and laboratory-developed assays are sensitive and reproducible with broad linear ranges. Further clinical evaluation is needed to determine the viral load cutoff that is predictive of posttransplantation lymphoproliferative disorders.

We compared a rapid slide latex agglutination test (LAT; Oxoid, Basingstoke, United Kingdom) that detects penicillin binding protein 2a (PBP2a) with MicroScan conventional panels (Dade Behring, West Sacramento, CA) for detection of oxacillin resistance in Staphylococcus aureus. The PBP2a LAT demonstrated 99% agreement with MicroScan oxacillin MIC results for 388 isolates of S. aureus. All 249 oxacillin-resistant isolates gave strong positive reactions in the LAT (100% sensitivity). Three of the 139 oxacillin-susceptible isolates were also strongly positive and one was weakly positive in the LAT (97.1% specificity). The three oxacillin-susceptible isolates with strongly positive reactions were further characterized. The mecA gene was detected in all three by PCR; one isolate was determined to be resistant to oxacillin by reference broth microdilution testing (MIC, 8 g/ml), one isolate was inducibly resistant to oxacillin (MIC of 16 g/ml after overnight induction), and one isolate remained susceptible regardless of the method used for testing. Sequence analysis of a 2.1-kb gene fragment of the mecA gene from the susceptible isolate revealed a one-base substitution at nucleotide position 1449 which results in a Met-to-Ile change for amino acid residue 483. This amino acid substitution has not been previously reported and may be associated with a change in the function of PBP2a resulting in oxacillin susceptibility. An additional 487 isolates were tested in parallel with the both the LAT and MicroScan panels using criteria in which only strong (3 to 4؉) or repeatedly weak (1 to 2؉) LAT reactions were considered positive, and the results showed 99.4% agreement. The PBP2a LAT provided rapid and reliable detection of oxacillin resistance and proved a useful adjunct to the phenotypic method. Both methods provided reliable detection of oxacillin-resistant S. aureus and facilitated the discovery of a novel, functionally impaired form of PBP2a.