In case the wife's health condition necessitates a blood transfusion, it is permissible for her to receive the blood donated by her husband or any other person. Unlike Rada` (breastfeeding which produces the legal impediment to marriage of milk-kinship), blood transfusion, no matter how large the amount, does not affect the marriage relationship in case one of the couple happens to donate his blood to his partner. Accordingly, the wife will not become unlawful to her husband by virtue of this donation. The same holds true if the husband receives blood transfused from his wife.
May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.