(A positive cross match means that the recipient has responded to the donor and that the transplant should not be carried out. A negative cross match means that the recipient has not responded to the donor and therefore transplantation should be safe.)
Tissue matching identifies certain proteins in your blood called antigens. Antigens are markers on the cells in your body, which help your body, tell the difference between self and non-self. This allows the body to protect itself by recognizing and attacking something that does not belong to it such as bacteria or viruses.
Your body also sees antigens on a transplanted organ that are different from its own and it sends white blood cells to attack the organ - when your body attacks the new organ, it will reject it. In order to help prevent rejection, I will take certain medicines called immunosuppressants. Although there are many different antigens, there are six, which have been identified as having an important role in transplantation. They are the A, B, and DR antigens. (DR and B being the most significant) There are two antigens for each letter and they are identified by numbers. So, your HLA type might look something like this:
You inherit these from your parents, three (A, B, and DR) from your mother and three (A, B, and DR) from your father. Children born of the same parents may inherit the same combination or a different combination of antigens. If you have brothers or sisters, there is a 25% chance that you will have inherited the same six antigens as one of them, a 50% chance of having three of the same antigens and a 25% chance of having none of the same antigens. Except for identical twins and some brothers and sisters, it is very rare to get an exact match between two people, especially if they are unrelated. The chance of finding an exact match with an unrelated donor is about one in 100,000.
Although the matching of antigens are considered during transplant it does not play a significant role, transplants are still performed into receipents where no antigens are in common and it has been proven that these patients do very well, some of them have never had a rejection episode while in other cases, patients who have had an exact six-antigen match have rejection occured because there are other antigens that have not yet been identified that may play a role in rejections. Unfortunately, there is no way of predicting who will experience rejection and it can occur at anytime.
Thus we draw the following conclusions:
- A living donor kidney is better than a deceased donor kidney. This finding is true at all levels of HLA (antigen) matching and over all time frames (three months, one year, five years, and 10 years). That is, even a zero match living donor organ has a better survival rate than a perfectly matched deceased donor organ.
- In general, the better the HLA match, the longer the graft survival. That is, if a choice is available, a closer match is preferred. This result becomes more pronounced over time. Graft survival rates are best with a perfect (six out of six) match, followed by a clustering of results for HLA matching of one to five antigens, with the lowest graft survival rates for a zero match. (Results for HLA mismatch have not been tested to see if the differences are statistically significant.)
- There have been modest improvements in graft survival rates when the 1996 - 2006, 1995 - 2002, and 1990 - 1998 periods are compared. The improvements are most pronounced for deceased donations, but the improvements are not sufficient to overcome the better survival rates of living donor organs.
- The level of HLA match does not matter when determining whether a person can donate. We have observed that transplant teams often do not consider HLA matching when identifying potential donors. The HLA match may be used as a tie-breaker if there is more than one living donor available.
- The level of HLA match does matter to graft survival: the better the HLA match, the better the kidney survival rate over time. Therefore, given a choice, a potential transplant recipient would prefer the highest HLA match available.
Thus considering the above statistics John and I had a 1/6 antigen match which seemed a bit daunting at first and as John said "felt like the wind was taken out of his sails". After doing some of my own research I contacted Ray to find out which one of the antigens was matched as the DR and B tends to play an important role if you would like to consider the antigen results. So any of the 3 type antigens DR, B or A antigens could have been a match but it was the DR antigen that was a match. I immediately contacted my Dr. in South Africa as I always also value his opinion and he confirmed the above that it was an added bonus that we had the DR match which is regarded as the most important antigen for organ transplants.
I also shared my findings with John and considering that a 0/6 living donor match is always better than a even a 6/6 deceased donor match this was wonderful news!
By now John has scheduled his final kidney function tests which determine the function of his kidneys and we are awaiting these final results around the 28th - 29th August.