The way I read it, the Watchtower interprets Acts 21:25 as follows:
"...But as for the gentiles who have become believers, we have sent them a letter telling them we decided that they must not eat any food that has been offered to idols, or the primary components of blood—namely red cells, white cells, platelets and plasma. However fractions of all primary components are permitted. Having said that, when it comes to fractions of any of the primary components, each Christian, after careful and prayerful meditation, must conscientiously decide for himself. “
Incredible, and they think themselves the voice of the Creator on earth!