My son donates plasma 2xs a week & was told his liver is putting stuff in his bloodstream that shouldnt be there. what could be the cause of this?

Transaminases?: I'm betting that junior has high transaminases ast and alt. His personal physician knows how to follow this up -- depending on what he already knows, he may be checked for hepatitis, hemochromatosis, wilson's and perhaps others. If no cause is found, getting in best aerobic shape may normalize them. Or he may have gilbert's non-disease and run a naturally high bilirubin. Best wishes.