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. Nephelometric Immunoassay Analyzers

Scope of this Product Comparison

This Product Comparison covers all types of dedicated nephelometric immunoassay analyzers.
These devices are also called: nephelometers, immunonephelometric assays.


Nephelometric immunoassay analyzers rapidly and precisely
measure concentrations of specific plasmaproteins (antigens or
antibodies) and/or therapeutic drugs by detecting light scattered
from antigen-antibody complexes. In some instances, these
instruments can also measure the in vitro formation rate of such
complexes. Most of the instruments can run assays on cerebrospinal
fluid, urine, or serum. The test results provide criteria for
diagnosing immunoproliferative diseases, immunedysfunctions or
deficiencies, hypersensitivities, and autoimmune diseases.

Principles of operation

As collimated (nondivergent) monochromatic light passes through a homogeneous test mixture, it is scattered,
reflected, absorbed, and/or transmitted by particles in suspension. The intensity of the scattered light is
proportional to the number of suspended particles; nephelometry is themeasurement of this scattered light.
When the particle size is less than one-tenth the wavelength of light used (e.g., certain plasma proteins, lipids,
small aggregates from early immunologic reactions), equal amounts of light are scattered away from and toward
the light source; such scatter is termed symmetrical or Rayleigh. If the particles are larger than the wavelength
(e.g., bacteria,blood cells, latex particles, later immunologic reactions of proteins), more light is scattered toward
the light source than away from it; this phenomenon is known as Mie scatter. If the size of the particle approaches
that of the wavelength, the scatter is predominantly directed away from the light source and is referred to as
Rayleigh-Debye scatter.

There are two basic types ofnephelometric immunoassays: direct nephelometric immunoassays, which
measure the reaction between antibodies and antigens such as
proteins, and indirect nephelometric immunoassays, which
measure the amount of incomplete antigens in the test sample.

UMDNS Information

This Product Comparison covers the following
device term and product code as listed in ECRI
Institute’s UniversalMedical Device Nomenclature
System™ (UMDNS™):

. Analyzers, Laboratory, Immunoassay, Nephelometric

In one indirect assay, the nephelometric inhibition assay (NIA),
low-molecular-weight antigens (such as therapeutic drugs) are
conjugated to carrier proteins and are known as developer
antigens. When the assay is performed, these developer antigens
compete withpartial antigens, called haptens, from the test

specimen for available antibodies. Specimen hapten-antibody complexes produce less scatter than developer
antigen-antibody complexes; therefore, any subsequent reduction in light scatter is proportional to the
concentration of haptens in the test specimen.
Latex particles can also be used in nephelometric immunoassays in whichantigen-antibody reactions cannot
form large enough immunocomplexes to create measurable changes in light scattering. The latex particle is coated
with an antigen or antibody. During the reaction with the corresponding specific antibody or antigen, the increase
in light scatter correlates to the concentration of the substance under analysis.
The two methods used by these devices for concentrationmeasurement are the end-point method and the
kinetic method. In the end-point method, the reaction mixture incubates until the end point, or equilibrium, of the
reaction is achieved. In the kinetic (or fixed-time) method, the reaction is monitored continuously as the reagents
and sample are mixed; the rate of change in absorbance over a fixed time is then determined and related to
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