Comparison of immunoglobulin determinations in pathological sera by radial immunodiffusion and laser nephelometry

Immunoglobulins G, A, and M were measured by radial immunodiffusion and by laser nephelometry in sera from 33 patients and in a preparation of purified colostral IgA. In general the results agreed for the two methods, with some exceptions attributed to the physicochemical characteristics of the immunoglobulins assayed: low-molecular-weight (monomeric) IgM gives falsely high values and IgA proteins (consisting predominantly of polymeric molecules) give falsely low values when assayed by radial immunodiffusion. Results from laser nephelometry apparently are not affected by the molecular-size characteristics of the proteins assayed.