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

Abstract

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.