Nephelometry
Encyclopedia
Nephelometry is a technique used in immunology
Immunology
Immunology is a broad branch of biomedical science that covers the study of all aspects of the immune system in all organisms. It deals with the physiological functioning of the immune system in states of both health and diseases; malfunctions of the immune system in immunological disorders ; the...

 to determine levels of IgM
IGM
IGM as an acronym or abbreviation can refer to:* Immunoglobulin M , the primary antibody against A and B antigens on red blood cells* International Grandmaster, a chess ranking* intergalactic medium* Intragroup medium - see: Intracluster medium...

, IgG, and IgA
IGA
Iga or IGA may stand for:-Given name:* a female given name of Polish origin. The name originates from the female given name Jadwiga and stands for gia,or gina in the USA....

.

It is performed by measuring the turbidity in a water sample by passing light through the sample being measured. In nephelometry the measurement is made by measuring the light passed through a sample at an angle.

This technique is widely used in clinical laboratories because it is relatively easily automated. It is based on the principle that a dilute suspension of small particles will scatter light (usually a laser) passed through it rather than simply absorbing it. The amount of scatter is determined by collecting the light at an angle (usually about 70 or 75 degrees).

Antibody and the antigen are mixed in concentrations such that only small aggregates are formed that do not quickly settle to the bottom. The amount of light scatter is measured and compared to the amount of scatter from known mixtures. The amount of the unknown is determined from a standard curve.

Nephelometry can be used to detect either antigen or antibody, but it is usually run with antibody as the reagent and the patient antigen as the unknown. (Clinical Immunology and Seriology 3rd Ed., Stevens, pg 127, F.A. Davis Company) In the Immunology Medical Lab, two types of tests can be run: "end point nephelometry" and "kinetic (rate) nephelometry".

End point nephelometry tests are run by allowing the antibody/antigen reaction to run through to completion (until all of the present reagent antibodies and the present patient sample antigens that can aggregate have done so and no more complexes can form). Unfortunately, the large particles will fall out of the solution and cause a false scatter reading, thus kinetic nephelometry was devised.

In kinetic nephelometry, the rate of scatter is measured right after the reagent is added. As long as the reagent is constant the rate of change can be seen as directly related to the amount of antigen present.
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