Given the patient's antibodies, what is the minimum number of donors that would need to be antigen typed to obtain two antigen-negative donors to crossmatch?

There are two ways to calculate the minimum number of donors to antigen type:

  1. "Intuitive": If 7.6% of donors are C-and Jk(a-) then 7.6 in 100 are negative for both antigens. If roughly 8 in 100 are negative for both, approximately 4 in 50 would be negative for both; and approximately 2 in 25 would be negative for both. To obtain two C-and Jk(a-) donors, at least 25 would need to be tested.
  2. The minimum number to antigen type can also be calculated using this formula:

    # of donors (x) = # required/# antigen-negative (as a decimal)
    x = 2/0.076 = 26.3

    Depending on how lucky you feel, the minimum number to type is between 25 and 30, with 30 being on the safer side.