Kidney transplantation · Before the transplant
Do you really need a perfect tissue match?
Blood type compatibility, tissue matching and the crossmatch test — explained by a transplant professor, without the myths that stop people from even asking.
The short answer
- No, you do not need a perfect tissue match. In living donor transplantation, tissue compatibility has largely lost the importance the public still gives it.
- Blood type matters far more than tissue type. These two are often confused.
- The widely repeated idea that "you need 50% compatibility" appears in no medical textbook.
- A positive crossmatch is not automatically the end of the road — the antibody type behind the result decides.
- Tissue matching still carries real weight in transplants from deceased donors — the rules are different there.
What is a tissue type, exactly?
Tissue typing is a blood test that shows part of your genetic structure. Just as with blood type, the question is whether the tissue types of the recipient and the donor fit one another.
Tissue types are sets of antigens inherited from your parents. They sit on the surface of almost all of your cells, they do not change during your lifetime, and they function as your individual code.
Everyone has six antigens that make up their tissue type, built from three basic characteristics: A, B and DR. You carry two of each — two A, two B, two DR — one of each pair from your mother and one from your father. Each characteristic has twenty or more known versions, which allows for hundreds of possible tissue codes.
A tissue type might be written as A1/A2, B7/B8, DR2/DR3. When doctors speak of "5 out of 6" or "full compatibility", these are the six values being compared.
Among these antigens, DR compatibility carries more weight than A or B. This is why most centres allocating a kidney from a deceased donor look for DR compatibility first, and call in the patients who show the closest overall match.
Does tissue compatibility decide whether a transplant succeeds?
This is where the answer differs sharply depending on where the kidney comes from.
For transplants from deceased donors, success depends to a large extent on tissue compatibility. Under Turkish law, a recipient must share at least two of the six tissue characteristics with the deceased donor, ideally including a DR match.
For transplants from living donors, the picture has changed. What was once considered decisive has turned out to matter much less than expected:
| Comparison | Kidney survival at 5 years |
|---|---|
| Transplant between identical twins (all six tissues identical) | Only 7% higher than a transplant with no tissue compatibility at all |
| No tissue compatibility, blood type compatible only | Approximately 80% |
| 5 out of 6 tissue compatibility | Approximately 80% — essentially the same |
Set that against the reality of dialysis: in Türkiye, roughly half of haemodialysis patients die within five years. When the difference between a "perfect" match and no match at all is a few percentage points, refusing a patient a transplant on tissue grounds costs far more lives than it saves.
For this reason patients should be offered the chance of transplantation regardless of tissue compatibility wherever a living donor is available.
"You need 50% compatibility for a transplant." Or 80%. Or some other figure that circulates among patients and their families.
These percentages appear in no medical textbook. Their only real effect is to discourage living donor transplantation — which means keeping people on dialysis who could have been transplanted. If someone quotes you a percentage threshold, ask them for the source.
Which matters more — blood type or tissue type?
Blood type, and by a wide margin. The two are frequently confused, but they are not equally important.
- Tissue-incompatible transplantation can be performed readily, especially with a living donor.
- Blood-group-incompatible transplantation can only be performed in selected patients, and requires special treatment protocols beforehand.
That second point is worth reading twice, because it is often presented to patients as an absolute barrier. It is not — but it is a genuine one that requires preparation, not simply a matching donor.
Does full compatibility guarantee the kidney will not be rejected?
No. Transplants that match on all six antigens do perform better, particularly from deceased donors. But a fully matched kidney can still be rejected.
The clearest evidence is that even transplants between identical twins — where every tissue is the same — can be lost after a period. This tells us there are important markers on cell surfaces beyond blood type and tissue type that can trigger rejection, and that matching alone does not tell the whole story.
The crossmatch test
The lymphocyte crossmatch (LCM) is the first test required after blood and tissue matching, for living and deceased donor transplants alike.
In this test the donor's blood is mixed with the potential recipient's. What is being looked for is whether the recipient carries antibodies that would react against the donor's kidney. Under normal circumstances these antibodies are part of how the body defends itself against infection.
If they are present in high amounts, the two bloods react and the test comes back positive. If a transplant were performed in that state, the kidney would most likely be lost within hours to days.
The risk of a positive crossmatch is higher in patients who have had a previous kidney transplant or a blood transfusion. This is why blood transfusions should not be given to dialysis patients unless genuinely necessary — each one can narrow the range of donors available later.
Does a positive crossmatch mean transplantation is impossible?
No. A positive result does not mean everything is over.
First, not every positive crossmatch blocks transplantation. The antibody type behind the result matters:
| Antibody type | What it means |
|---|---|
| IgG | Transplantation is not possible at that time |
| IgM | Transplantation can be performed without difficulty |
In other words, a crossmatch positive on IgM antibodies does not stand in the way of transplantation at all — and this distinction is not always explained to patients when they are given the result.
Second, a crossmatch result describes a moment in time, not a permanent verdict. Antibody levels can change, and transplant centres do work with selected patients whose first crossmatch was positive. Whether that applies in your case depends on the antibody type, the level, and the protocol of the centre assessing you.
If you have been told that a positive crossmatch closes the door, two questions are worth asking: which antibody type was found, and was the test repeated.
What this means if you are looking for a transplant
Three practical conclusions follow from all of the above:
- A living donor who is blood type compatible is worth evaluating, even if the tissue match looks poor on paper.
- A percentage figure is not a decision. Ask which antigens matched, whether DR is among them, and what the crossmatch showed.
- A "no" based on one test deserves a second opinion — particularly a no based on a positive crossmatch or on blood group incompatibility, both of which have established treatment routes.
Prof. Dr. Murat Tuncer
Nephrologist and transplant physician. Author of Kidney Transplantation — With Questions and Answers (Istanbul, 2020), written to answer the questions his own patients ask most often. Published research includes the first ABO-incompatible kidney transplantations performed in Türkiye.
Have your reports reviewed before you travel
Send us your test results and we will tell you honestly whether transplantation is realistic in your case — including where a previous "no" may be worth revisiting.
Medical disclaimer. This article is general information adapted from a published book. It is not personal medical advice, it does not establish a doctor–patient relationship, and it cannot replace assessment by the physician treating you. Transplant eligibility depends on findings specific to each patient and donor. Always consult your own nephrologist or transplant centre before making decisions about your treatment.
References
- Knoll G, Cockfield S, Blydt-Hansen T, et al. Canadian Society of Transplantation consensus guidelines on eligibility for kidney transplantation. CMAJ 2005;173(10).
- Tuncer M, Gurkan A, Erdogan O, Yucetin L, Demirbas A. Lack of impact of human leukocyte antigen matching in living donor kidney transplantation: experience at Akdeniz University. Transplant Proc 2005;37(7):2969–72.
- Tuncer M, et al. ABO-incompatible kidney transplantation: first cases in Türkiye. Transplant Proc 2012;44(6):1703–5.
