Assay Characteristics

Because of its narrow therapeutic index, tobramycin concentrations are frequently monitored. The thera- 

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The USP requirements for assay validation are very close to the ICH proposal. Here, three categories are distinguished. Category I corresponds to ICH assay, category II corresponds to ICH determinations of impurities. The additional category III includes analytical methods for the determination of performance characteristics (e.g., dissolution, drug release). For this category, the ICH assay characteristics are always sufficient. The objective of the analytical procedure... 

As previously alluded to, functional methodology is not, as yet, fully standardized. The literature is bulging with methods, many times improvised on the spur of the moment to fit the needs and instruments of the researcher, with inadequate preliminary examination or statistical evaluation. This section will attempt to organize a general system of methodology for protein food products. In it, a general plan of assays will be followed by criteria for choice of assay, characteristics of Model Tests, and, finally, characteristics of Utility Tests. 

Finally, the same questions should be asked in a critical manner of the in-process and final acceptance tests for raw materials, in-process intermediates, and final product. Imported and research tests often do not make good quality control laboratory tests. The quality control tests need to be robust, meaningful, validated, and reproducible. Many research assays are narrow in scope, unstable, user-dependent, and complex, and they also yield wide-ranging results. These assay characteristics are exactly the opposite of what is needed in quality control therefore, all analytical methods and assays must be critically evaluated for relevance and validated for use. 

Serum was either used for measuring FSH immediately or frozen until hormone determination. FSH and creatinine in urine were determined immediately. Additional urine samples were obtained to determine assay characteristics. In order to determine storage conditions, urine samples were stored at room temperature, at 4°C, at -20°C without any addition, and at — 20°C with addition of glycerol. After 1 and 4 weeks, FSH and creatinine were determined again. 

The discontinuous method measures activity by separating the product from the substrate. Assays characteristic of this group usually require two steps, since separation often does not include detection. Thus, first, the substrate and the product are separated, and usually the amount of product formed is measured. Assays that use radiochemical substrates are included in this group, since radiochemical detectors are unable to differentiate between the radiolabel of the substrate and that of the product. Examples of enzymes whose assay methods fall into this category are legion, and these approaches characterized by a separation step. 

Qualitative conclusions of the presence or absence of cross-reactants in the sample matrix can easily be drawn by measuring the analytical response at different dilutions of the sample non-parallel curves for the standard and sample demonstrate a lack in structural identity [1]. This simple result is based on the principle that differences in molecular structme are likely to lead to differences in reaction thermodynamics and kinetics, even when identical epitopes are involved in the antibody-antigen reaction. Such differences are generally manifested as differences in the apparent affinity constants governing the reactions, which can be revealed as alterations of assay characteristics [1,16]. 

Initial molar ratio hapten/label Assay characteristics ... 

Important assay characteristics for immunochemical methods include (1) limit of detection, (2) precision, and (3) turnaround time. 

M Lackmann, et al., Radioimmunoassay for the detection of active site specific thrombin inhibitors in biological fluids—Assay characteristics and quantitation of recombinant hirudin. Thromb Res 63 595, 1991. 

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