'50 percent more kidney transplants through Cross-over+'

Nephrologist Jacqueline van de Wetering was closely involved in the development of Cross-over+ by Erasmus MC. She is on the steering committee overseeing its national implementation.

Kristiaan Glorie is an econometrician and director of Erasmus Q Intelligence, which translates university knowledge into societal applications. He and his colleagues developed the new algorithm.

Long waiting times

Jacqueline: ‘In 2002, we developed Cross-over for patients with a kidney donor who was willing to donate, but not to them specifically. This was either due to an incompatible blood type or because the patient had antibodies against the donor's tissue markers. By pairing couples via an algorithm, we made donor exchange possible.

We noticed, however, that people with blood type O or B, or with antibodies against many tissue markers, had to wait a very long time. We wanted to do something about that. Furthermore, there have been many developments with living donors since 2002. We can sometimes transplant across blood types thanks to filters. Transplantation is also sometimes possible if someone has antibodies against the donor's tissue, but not too many. Additionally, through Cross-over, we are matching more altruistic donors—who do not come with a patient—which makes more matches possible.'

Cross-over+

'In the new Cross-over+, we have integrated all of this. For patients who have been waiting a very long time, we can check more options, such as transplanting across blood types. As a result, we have already been able to transplant several long-waiting patients. That is why the NTS is going to roll this out nationally. As far as I am concerned, all donors and patients should be in Cross-over+. That allows for much better combinations, which reduces the risk of rejection in the long term.’

50 percent more transplants

Kristiaan: ‘Erasmus Q Intelligence is affiliated with the econometrics department of Erasmus University Rotterdam. Econometrics is fundamentally a combination of mathematics, IT, and economics. It often deals with distribution issues, and that is a bridge to transplantation. We have developed a new algorithm for the allocation of kidneys in Cross-over+. The method of exchange turns out to be very decisive for the number of transplants. Simulation research from Erasmus MC shows that this can increase by almost 50 percent. For highly immunized patients, the increase is 100 percent, and for those waiting a long time, it is even 200 percent.'

Integrated techniques

'Previously, you had separate programs: nationally there was Cross-over, locally people performed transplants across blood type and antibody barriers. Cross-over+ integrates all these possibilities into one program and calculates the best outcome using mathematical techniques. By utilizing synergy effects, the end result is much better than the sum of the individual programs.

The mathematics behind it is quite complex. The trick is to keep it explainable. For that, it was important to listen carefully to the professionals involved and to delve into the medical side. This allowed us to translate it effectively. By collecting data in practice, we can further optimize the program in the coming years.'

This article is from Transparant magazine (no. 96).
Curious about more stories and background? Read the full magazine here.