[stw]

Please could someone explain to me or give me www-links where is explained what exactly a differential radioassay is an how it works.

Thanks in advance

Stephan

[viking]

first you need to know what a radioassay is and then you need realize that a radioassay and a radioimmunoassay are essentially the same.

In radioimmunoassays, radioactive iodine (125 I) is usually used to label the antigen. The immune complexes are separated from the unbound molecules by precipitation with centrifugation after reaction with secondary antisera and precipitating reagents (e.g. polyethylene glycol).[7] These radioimmunoassays may require special handling and licensure to ensure safety of the radioisotopes and are labor-intensive. The statistical counting errors associated with the relatively low radioactive counts and the poor reproducibility associated with the multiple manual steps generally necessitate that most laboratories perform the measurements in duplicate.[8] Even when the averages of duplicate measurements are used, many manual radioimmunoassays have coefficients of variation between 10% and 15%.

It is important that key quality control parameters for radio-immunoassays be carefully monitored. In addition to NSB, another key quality control parameter is the percentage binding of the radiolabel when zero antigen (Bo) is present. As the label deteriorates, because of aging, the binding often decreases, resulting in a less reliable assay.

Another important quality control parameter is the slope of the dose-response curve. This parameter can be tracked by monitoring the concentration corresponding to half-maximum binding (50% of B/Bo). If this concentration increases significantly, the slope of the response curve decreases and the assay may not be capable of reliably measuring patient specimens at clinically important concentrations.

Many commercial kits and automated immunoassays today use nonisotopic signal systems to measure hormone concentrations. These assays often use colorimetric, fluorometric, or chemiluminescent signals rather than radioactivity to quantitate the response. The advantages of these alternate signals are biosafety, longer reagent self-life, and ease of automation. On the other hand, these signals are more subject to matrix interferences than radioactive iodine.

Radioactivity is not affected by changes in protein concentration, hemolysis, color, or drugs (except for other radioactive compounds), whereas many of the current signal systems may yield spurious results when such interferences are present. In addition, many of today's automated immunoassays are read kinetically before the reactions reach equilibrium. This step accentuates the effects of matrix differences between the reference standards and patient specimens. Later in this chapter potential trouble-shooting steps are outlined to help clinicians evaluate the integrity of test measurements when spurious results are suspected.

Solid-phase reactions often are used in current immunoassays to facilitate the separation of the bound antibody-antigen complexes from the free reactants. [9] Three frequently used solid-phase materials are (1) microtiter plates, (2) polystyrene beads, and (3) paramagnetic particles. [10] Typically, the antibody is attached to the solid phase, and the separation of the immune complexes from the unbound moieties is accomplished by plate washers, bead washers, or magnetic wash stations, eliminating the need for centrifugation. Other novel ways of accomplishing this separation is to attach high-affinity linkers to antiserum, which then can be coupled to a complementary linker on the solid phase.


This is the best that I have for now but good luck searching.