Figure 2 :Balanced (a) and unbalanced (b) two way paired kidney donation. Balanced two way: Donor D1 and recipient R1 (related pair) has blood group A and B respectively. Donor D2 and recipient R2 (related pair) has blood group B and A respectively. These ABO imcompatibility does not allow two transplantations. In a balanced PKE donor D1 gives kidney to recipient R2 (Unrelated pair) and donor D2 gives kidney to recipient R1 (Unrelated pair). Unbalanced two way: Donor D1 has blood group O and related recipient R1 has blood group B. So donor D1 can donate to R1. The other pair, donor D2 has blood group B and the related recipient R2 has blood group O. If donor D1 donates to recipient R2 (unrelated) and donor D2 donates to recipient R1 than it is known as unbalanced two way PKE.