Quantifying plasma proteins based on the specific reaction of the protein being measured with highly specific antisera.
Precipitants are antigen-antibody complexes, which show up in solutions as turbidity and scatter incident light.
The nephelometer uses a light -emitting diode at a high wavelength (usually >600 nm) to detect variations in light scatter as antigen-antibody complexes are formed. When the light rays encounter insoluble complexes such as fibrin strands, they are scattered in both forward (l80-degree) and side (90-degree) angles.
Instruments employing this type of measuring system detect the amount of agglutination of particles by reading the increasing amount of light scattered at a 90-degree angle as agglutinates are formed. The timer is triggered to stop when the amount of light scatter reaches a specific predetermined level.
This method of endpoint detection is in contrast to the photo-optical systems, which sense decreased light transmission at 180 degrees due to the opaqueness of the sample in a cuvette when fibrin is formed.