It is not correct to draw an analogy between donating blood and breastfeeding to prove that someone is a mahram
Question

                I know that breastfeeding establishes the relationship of being a mahram, and that if a woman breastfeeds a child she becomes his mother through breastfeeding (radaa’ah). Is it correct to draw an analogy between blood transfusion and breastfeeding?.
Praise be to Allah.This analogy is not 
    correct. The relationship of mahram that is proven in sharee’ah applies only 
    in the case of breastfeeding. This has been stated by the consensus of the 
    Fiqh Council. 

    Majallat al-Buhooth al-Islamiyyah, 
    35/343. 

    The Standing Committee was asked: 

    A man had blood taken from him to be given to his wife. Does 
    that have any effect on his married life with her? 

    They replied: 

    Perhaps the questioner is thinking of an analogy between 
    blood and the milk that establishes the relationship of a mahram. This 
    analogy is not valid for two reasons: 

    1-Blood is not a source of 
    nourishment as milk is;

    2-That which establishes the 
    relationship of a mahram according to the text is breastfeeding that fulfils 
    two conditions: (i) that the breastfeeding occurs five or more times; (ii) 
    that that takes place within the first two years of the child’s life. 
    

    Based on this, the blood that has been taken from you and 
    given to your wife does not have any affect on your married life. And Allaah is the Source of strength. 

    Majallat al-Buhooth al-Islamiyyah, 4/332.