The variable influence of an α component in pregnancy plasma on four different assay systems for the measurement of pregnancy-specific β1 glycoprotein

Four methods (radioimmunoassay, electroimmunoassay, laser nephelometry and kinetic immunoturbidimetry) have been evaluated for the measurement of proteins with pregnancy-specific β 1 glycoprotein immunoreactivity. The influence of two maternal plasma proteins with different electrophoretic mobilities (α 2 and β 1 ) but with similar antigenic determinants has been assessed in each assay system. The radioimmunoassay method, which utilises a homogeneous preparation of pregnancy-specific β 1 glycoprotein for the preparation of iodinated tracer, and the kinetic immunoturbidimetric assay which measures antigen-antibody complex formation over the first minute of the reaction, were both considerably more specific for the β 1 component of pregnancy specific β 1 glycoprotein immunoreactivity than the laser nephelometric or electroimmunoassay methods.