The effect of pH on radioimmunoassay of LH and FSH.

Freezing and thawing of human serum produces alkaline changes in the pH. Weak buffers were of insufficient capacity to compensate for these pH changes. Thus the effect of serum pH on modified solid-phase and double-antibody radioimmunoassay (RIA) of LH and FSH was studied. Pooled postmenopausal serum standardized against the Second International Reference Preparation of Human Menopausal Urinary Gonadotropon was used as a laboratory standard. In the solid phase RIA for LH and FSH, slopes with the greatest maximum binding were obtained at pH 6.4, whereas for the double-antibody method best results were obtained at pH 8.0. Since there is individual variation in the pH of various serum samples, different values will be obtained from samples containing the same amount of hormone. It is sum samples be standardized by the use of buffers with the capacity to keep the pH of the serum constant and that serum standards be dialyzed.