Nucleic acid-based testing assays

Fig. 19.8d). The data indicate that the multiplexed assay is not only DNA sequence-specific, but also can quantitatively and simultaneously identify the different food-home pathogens. Obviously, the multiplex related labor and sample processing reduction, simpficity, and breadth of testing options on one device, and combinational power of multiple biomarkers, [41] will make the assay even more attractive for the nucleic acids-based diagnostics. 

The viral load test quantifies viremia by measuring the amount of viral RNA. There are several methods used for determining the amount of HIV RNA reverse transcriptase-coupled polymerase chain reaction, branched DNA, and nucleic acid sequence-based assay. Each assay has its own lower limit of sensitivity, and results can vary from one assay method to the other therefore, it is recommended that the same assay method be used consistently within patients. 

All of these tasks can now be addressed with a family of novel tests collectively named product-enhanced reverse transcriptase (PERT) assays. PERT assays combine the broad detection range of RT tests with the high sensitivity of nucleic acid amplification procedures. PERT assays are based on the selective enhancement, by polymerase chain reaction (PCR) or one of the various... 

Both the MTD test and the Amplicor test have a sensitivity of 95% to 98% when using APB smear-positive respiratory specimens, and the specificity ranges from 99% to 100%. However, early studies showed that the sensitivity for APB smear-negative specimens was -50%. Based on these data, it was clear that the test could not he used to rule out MTb infection on smear-negative respiratory specimens. This further limited the clinical utility of these tests, because it became clear that the nucleic acid testing would be used to supplement the AFB smear and culture rather than replace these testing modalities. Another limitation of the currently available nucleic acid assays is that they can be used only on specimens from patients who had not received antituberculosis therapy within the past 12 months. This limitation was included because DNA can persist in respiratory secretions (and other body fluids) for months after the mycobacteria are no longer viable. 

Assays based on measurements of specialized functions and viral products For viruses that do not form plaques or induce CPE in cell cultures. Determination of virus specific parameters, e.g., hemagglutination and hemadsorption tests, inhibition of cell transformation and immunological tests detecting antiviral antigens in cell cultures. Reduction or inhibition of the synthesis of virus specific polypeptides in infected cell cultures, e.g., viral nucleic acids, viral genome copy numbers or the uptake of radio labeled precursors. 

Immunoassays presently form probably the most active area of exploitation of CL, ECL and BL, as evidenced by the extensive commerciahzation of luminescent immunoassay analyzers and test kits. Among these, acridinium ester-based CL assays for alkaline phosphatase and amplified CL assays using peroxidase labels have become the most widespread [207, 208]. Besides immunosassays CL and BL have been used in nucleic acid assays [209-211] and in cellular studies concerning, for instance, phagocytosis [212]. ECL immunoassays based on ruthenium trisbipyridyl labels are now becoming popular in clinical immunoassay analyzers [213]. 

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