Influence of the pH on the antigen-antibody coupling in angiotensin I radioimmunoassay. Its consequences for the determination of the plasma renin activity.

The antigen-antibody complex formation in the angiotensin I radioimmunoassay appears to be influenced by the pH of the radioimmunoassay incubation mixture. This may lead to erroneous results in the determination of the plasma renin activity, when an aliquot of a plasma sample, buffered at pH 6 for optimum renin activity is brought into a radioimmunoassay mixture of another pH, while the radioimmunoassay standards are not corrected for this pH shift. In our experiments we studied this general pH effect, and evaluated the effect on the New England Nuclear Angiotensin I radioimmunoassay procedure. We propose a slight modification of this radioimmunoassay kit.