Qualitative assays

Qualitative tests for the presence of pectinesterase, based on a color change of such indicators as Bromothymol Blue or Bromocresol Green, after de-esterification of pectin, are simple and very useful these tests are used as drop tests when checking chromatographic columns85,97 100 or for a qualitative assay of pectinesterase in culture filtrates, using the cup-plate method.113... 

The subjectivity of qualitative assays and the unavailability of rigorous IQC procedures place additional demands on the analyst and on laboratory organisation. Consequently ... 

The lack of adequate IQC for subjectively interpreted qualitative assays is a real cause for concern, but with properly documented methods, carefully maintained infrastructure and good training, clinically reliable results are achievable, and we will explore this further in the following section on EQA. 

WADA) TWA-DA (2010) Identification criteria for qualitative assays document td2003idcr... 

These qualitative assays show that one-armed cationic guanidiniocarbonyl pyrrole receptors can indeed effectively bind tetrapeptides even in water. Molecular modeling studies suggest a complex structure as shown for one specific example, the receptor Val-Val-Val-CBS, in Figure 2.3.11. Receptor and substrate form a hydrogen bonded //-sheet which is further stabilized by additional hydrophobic interactions between the apolar groups in the side-chains. Recognition of the tetrapep-tide thus seems to be controlled by a fine balanced interplay between electrostatic and hydrophobic interactions. 

Both techniques can be applied to most experimental models of apoptosis, including cells in culture and biopsies. In addition, techniques based on the cleavage of synthetic caspase substrates can be applied to caspases, activated in vitro and in vivo [82, 83], Whereas Western blotting is time consuming and mainly a qualitative assay, the detection of caspase activity by cleavage of synthetic substrates is a quantitative, relatively fast and sensitive method [82]. However, both techniques do not provide information about the type and distribution of the cells with activated caspases in the tissue examined. 

Standardization Classically, to standardize means to compare with or conform an assay of unknowns to established standards. In quantitative analytical work numbers readily allow for conforming to such standards. In semi-quantitative or qualitative assays such as immunocyto- or immunohistochemistry, which frequently conclude with an opinion, only subjective comparisons to carefully selected tissue and reagent controls can be used to monitor and maintain excellence. 

Immunoassays, electrochemical — A quantitative or qualitative assay based on the highly selective antibody-antigen binding and electrochemical detection. Poten-tiometric, capacitive, and voltammetric methods are used to detect the immunoreaction, either directly without a label or indirectly with a label compound. The majority of electrochemical immunoassays are based on -> voltammetry (-> amperometry) and detection of redox-active or enzyme labels of one of the immunochemical reaction partners. The assay formats are competitive and noncompetitive (see also -> ELISA). 

The authors describe an ultrasensitive method that measures RT activity. The assay adopts polymerase chain reaction (PCR) amplification for detecting the cDNA product of the reaction, and therefore was named Amp-RT (3,4). Amp-RT measures the ability of a sample to produce a DNA copy of a known heteropolymeric RNA template by extending a complementary DNA oligoprimer. The RNA template used in Amp-RT is a sequence from the genome of the encephalomyocarditis virus. This chapter describes in detail the Amp-RT method and its use as (1) a qualitative assay for the generic detection of retroviruses, (2) a quantitative method to measure virus loads of the human immunodeficiency virus type 1 (HIV-1), and (3), a screening method for susceptibility of HIV-1 to RT inhibitors. 

Bioanalytical methods are classified according to the kind of results they provide. Qualitative assays provide information about the presence or absence of the analyte, whereas quantitative assays give the analyte concentration and the uncertainty in this value, in the sample. Semiquantitative methods give an estimate of concentration and are used to determine whether analyte is present at a level that is above or below a reference concentration therefore the report can state if the concentration in the sample is higher, similar, or lower than the reference value. 

Reporting results for qualitative assays in infectious disease is simple The nucleic acid is either present or not detected in the patient specimen. Further relevant information that is useful when reporting results includes the detection limit and specificity of the test and the rate of inhibition for a given specimen type, particularly for assays that do not contain an inhibition control. 

Several qualitative assays have been approved by the FDA for the detection of HCV RNA in plasma or serum specimens (Table 42-7). The AmpHcor HCV test and the COBAS Amplicor HCV test (Roche Diagnostics, Indianapolis) are based on RT-PCR technology the COBAS test allows for... 

Biomarker assays (as other bioassays) may be classified into definitive quantitative assays, relative quantitative assays, quasi-quantitative assays, and qualitative assays with varying degrees of validation requirements (Table 5.5-3) [14, 15]. For definitive quantitative assays, a well-defined or characterized standard of the biomarker is available. In the case of relative quantitative assays, calibration is performed with a standard that is not well characterized, not available in pure form, or not representative of the endogenous biomarker. Results from these assays are... 

Parameter Definitive Quantitative Assay Relative Quantitative Assay Quasi- Quantitative Assay Qualitative Assay... 

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