Steroid radioimmunoassay--effect of shortened incubation time on specificity

Use of a briefer incubation interval in several steroid radioimmunoassays markedly increases cross reactions with some closely related steroids. The dissociation rates of the various steroid/antibody complexes play a critical role in determining the specificity of the antiserum, and the maximum specificity of an antiserum will be exploited only if it is incubated to equilibrium. The commonly used method for estimating the time required to reach equilibrium--i.e., the time required for the %(B0/T) value to "plateau"--grossly underestimates the true interval required, and we suggest that the minimum incubation period for steroid radioimmunoassay should be based on a knowledge of both the dissociation and the association rate.