The Ineluctable Logic of the Paired Donation program

The Ineluctable Logic of the Paired Donation program

I have gone through three rounds in the Kidney Paired Donation (KPD) program, two of them teamed with two willing but incompatible donors. No match has been found for me. With some time on my hands, I began to think about the likelihood of a match being found. Based on blood type distribution alone, here is what I have realized.

First of all Rh (+/-) does not matter when it comes to organ transplants so I’m combining the Canadian statistics for Rh positive and negative factors into one:

Blood Type

Percentage 46 42 9


As you can see, Type O is the most common, followed closely by Type A.

Second, let’s take a look at which blood type can donate to which blood type:

Donor Type

Recipient Type O, A, B, AB A, AB B, AB


On the donor side, note that Type O can donate to any recipient type. On the recipient side, note that AB can receive from any donor type. Note further that Type O can only receive from a Type O donor.

So, let’s put these statistics together and consider them in light of the fact that I am a potential Type O recipient and my friends are potential Type A donors.

On the face of it, it doesn’t look that bad. I can only receive a kidney from a Type O donor but that is the largest blood group so I have a relatively large pool to draw from. Furthermore, my potential donors are from the second-largest blood group so you would think that there would be substantial demand for a kidney donor with Type A blood. The paired donation program should work well.

That is not the case, however. Let’s imagine that someone with Type A blood needs a kidney transplant. She makes it known to her friends and relatives. Since she can receive a transplant from a Type O or a Type A donor, she can draw on 86% of the population. Consequently, it is less likely that she will need to enter the KPD program. There is therefore relatively little demand for Type A donors (my two friends) within the KPD program. The possibilities for an exchange seem less likely.

Now consider someone with Type O blood who needs a kidney transplant (me). He can only receive a transplant from a Type O donor. But let us further consider that the Type O donor can donate an organ to any blood type. A type O donor, if he becomes aware of a friend or relative who needs a kidney, can donate to that person directly, irrespective of the recipient’s blood type, so there is no need to enter the KPD program in order for the friend to receive a compatible kidney transplant. There is therefore relatively little supply of Type O donors in the KPD program.

The ineluctable (always wanted an occasion to use that word) logic of the KPD program is that my situation of being a potential Type O recipient, even with two potential Type A donors, means that the chances of a match on the basis of blood type alone are vanishingly small.

The Saving Grace

However, there are in fact Type O potential recipients who have been matched in the KPD program. The saving grace, if that is the right term, is that blood type is not the sole determinant of compatibility. We carry antibodies within us and these antibodies complicate the matching process. A potential recipient might carry antibodies that will attack the otherwise compatible Type O kidney were it to be transplanted into a given person. For that reason, there are potential Type O donors and potential Type A recipients in the KPD program, and enrolling in the program is not a hopeless or lost cause. It just means that I may have to stretch out my expectations when it comes to how quickly a match will be found.

Is there something that can be done about this? Well, I am not one to approach others directly to ask to have themselves tested as possible living donors, but if you have not yet done so, please register as an organ donor. We are, after all, mortal beings, and once we are dead, we have no more need for our organs. Consider such registration a basic part of your will and estate planning, and consider as well, that you have within you the potential to save up to eight lives. Isn’t that a legacy worth leaving?


For the Kidney Paired Donation program:

To register as an organ donor upon your death (select the link to your province):



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