Assay of Anti-D Activity by Two Radioimmunoassay Techniques Using Purified 125I-Labelled Anti-D

Abstract

Two methods are described for the estimation of anti-D activity in immunoglobulin preparations which are based on the radioimmunoassay inhibition techniques. In one of the methods, estimates were made under equilibrium conditions in a solution of normal ionic strengh. In this method, the assay is affected both by the concentration of the anti-D and the value of its equilibrium constant. This method did not correlate well with the standard assay method using 125I-labelled anti-IgG. In the second method, conditions were modified so that measurements were made at non-equilibrium conditions and in a solution of low ionic strength. Under these conditions, the assay is mainly dependent on concentration of anti-D, although it is influenced by the rate of association of anti-D with red cells. The second method correlated well in 24 out of 27 instances with the concentration of anti-D measured by the method using 125I-labelled anti-IgG.