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©2013 UpToDate ® Print Email Calculating availability of blood in a patient with multiple alloantibodies Transfusion candidates with known antibodies require blood negative for that antigen. The ease of finding such blood is inversely proportional to that antigen's frequency in the donor population (ie, the less common the antigen, the easier it will be to find compatible [ie, entigen negative] blood). In addition, the blood needs to be matched for the patient's ABO and Rh(D) type, since A, B, and Rh(D) are potent antigens. Blood group Frequency of antigen POSITIVITY (white population) O 45 percent A 40 percent B 11 percent AB 4 percent Blood group Frequency of antigen NEGATIVITY (white population) Rh (D) 15 percent K 91 percent Jk(b) 28 percent Fy(a) 37 percent To estimate the availability of blood, one multiplies the percentage of antigen-appropriate blood in the population for each of the antigens involved. In the example given in the text for a patient with Type O Rh negative blood, with anti-K, anti-Jk(b), and anti Fy(a), the percent of blood available is calculated as shown below: O positive (0.45) x Rh negative (0.15) x K negative (0.91) x Jk(b) negative (0.28) x Fy(a) negative (0.37) = 0.006. Thus, six out of one thousand randomly collected units should be compatible.