Cow milk fat interferes with prolactin radioimmunoassay

The concentration of prolactin (PRL) in fat-free cows milk was one-third that of whole milk while the values were similar for milk from the goat. A number of experiments were performed to determine if PRL was present in cow milk fat. The results indicate that cow milk fat introduces an artifact in the double antibody PRL RIA which overestimates the amount of prolactin in whole cow milk.