The interference of endogenous antibodies to bovine lactalbumin in the radioimmunoassay of human lactalbumin in serum.

Using a radioimmunoassay for the milk protein lactalbumin in human serum, we have found that falsely high results can be caused by cross-reacting human antibodies to bovine lactalbumin. A reliable method of circumventing this problem is described. When such interference had been eliminated, circulating lactalbumin was not detected in normal men or post-menopausal women, but could still be found in a proportion of non-pregnant, non-lactating pre-menopausal women.