Should an altruistic organ donor be allowed to restrict their donation to a specific group of people? (e.g. women, gingers)

An extreme version of this is: What should the German health service do if someone says they are willing to donate a kidney as long as it doesn't go to a Jew?

On the one hand, nobody is forced to donate a kidney and by forbidding this we're making things worse for an innocent patient. On the other hand, it can be seen as the state sanctioning this kind of discrimination.