Watch how the WTS "reasons" on that:
*** w75 4/1 pp. 215-216 Are You Guided by a Sensitive Christian Conscience? ***
CONSCIENCE AND EMPLOYMENT
7 Employment is an area that brings up many problems calling for the exercise of Christian conscience. Some forms of employment, such as making idols, working in a gambling establishment or being employed by a false religious organization, are clearly contrary to the Scriptures. So Christians shun these. (1 John 5:21; Col. 3:5; Rev. 18:2, 4, 5) Not all employment matters, though, are that clear-cut. Certain employment may be in a "gray area," so to speak. And sometimes, while one’s basic work is unobjectionable, one may be asked occasionally to do something questionable. So conscience can be involved.
8 For example, there are employment problems involving blood. The Bible states plainly that God’s servants should not feed on blood. (Gen. 9:3, 4; Acts 15:19, 20) Hence, Jehovah’s Christian witnesses do not eat food containing blood, such as blood sausage, or accept blood transfusions. But what if, on your job you were asked to handle blood or blood products occasionally? Would your conscience permit that? A Witness in Colorado worked in a hospital as the chief medical technician running tests of various types on body tissue and fluid. Among the many things he was expected to test were blood samples. Sometimes it was simply to check a patient’s blood for the level of sugar or cholesterol. But at other times it was to cross match for transfusion purposes. Could he do that?
9 This Christian gave careful thought to the matter. It could be seen that it would not be right for a Christian to work exclusively for a blood bank, where everything was devoted to an end that was in violation of God’s law. But that was not his situation; he ran tests of many kinds. Also, if one were a doctor responsible for the decision, one could not order a blood transfusion for a patient, any more than a Christian store owner could order and stock idols or cigarettes. However, this technician realized that in connection with blood he was merely running a test, even as a nurse might have taken the sample, a messenger might have delivered it to the laboratory and someone else might administer a transfusion or other medication on a doctor’s orders. He reflected on the principle at Deuteronomy 14:21. According to that text a Jew finding a carcass of an animal that died of itself could clear it away by selling it to a foreigner who was not under the Law’s restrictions about animal flesh not drained of its blood. So the technician’s conscience at that time allowed him to run blood tests, including those of blood for transfusions to patients who did not care about God’s law on blood.
10 Is that how your conscience would have reacted? If not, for the sake of discussion, ask yourself whether your conscience would permit you as an employee to bring the blood sample to the laboratory for testing. Or, taking yet another step farther away from the actual transfusion, could you as a truck driver deliver the testing equipment to the hospital? Or would your conscience let you make glass from which such equipment might be produced? It is clear that not all these things reasonably can be viewed as direct contributions to violating God’s law on blood. But where does one "draw the line"? Here is where conscience comes into play. While the Christian must avoid things that are unmistakably in conflict with God’s law, he is called upon to use his conscience in settling many matters. Would your conscience serve you well in such situations? Is it sensitive?
11 In this particular case, after many years of running tests, the technician began to be troubled by his conscience. It was not as if someone else should or could tell him that he was doing wrong. Nor was he looking for someone else to make his decisions for him. But he began to think: "Is it consistent to talk of neighbor love, and yet contribute, in part, to my neighbor’s breaking of God’s law?" (Matt. 22:39; Acts 21:25) Appreciating his Christian duty to support his family, he discussed the matter with his wife. (1 Tim. 5:8) Together they agreed that, if his conscience was troubled, it would be better to make a change. He left his $15,000-a-year job and began doing cleaning work, though he started off earning just $3,600 a year.
*** w64 11/15 pp. 682-683 Employment and Your Conscience ***Christians in the medical profession are individually responsible for employment decisions. They must bear the consequences of decisions made, in keeping with the principle at Galatians 6:5. Some doctors who are Jehovah’s witnesses have administered blood transfusions to persons of the world upon request. However, they do not do so in the case of one of Jehovah’s dedicated witnesses. In harmony with Deuteronomy 14:21, the administering of blood upon request to worldly persons is left to the Christian doctor’s own conscience. This is similar to the situation facing a Christian butcher or grocer who must decide whether he can conscientiously sell blood sausage to a worldly person.