Renal Graft Survival
Transplanted kidney survival is dependent on various factors, including how well it matches the recipient and whether it comes from a live or cadaveric donor.
Graft (transplanted kidney) Survival is the length of time transplants function well enough to keep recipients from either needing initiation of (or return to) dialysis, or another transplant. This is influenced by two main things:
1. How well the donor kidney cells match those of the recipient.
This is determined by tissue typing, using human leukocyte antigens (HLA); these antigens are tiny protein structures on white blood cells (WBC), as well as other body cells (including kidney cells) that are important determinants of the immune response. The more disparate the HLA between the donor kidney cells and those of the recipient are, the greater the immune response (rejection). Even though HLA typing does not detect all antigenic differences, it is useful in predicting graft survival and in deciding which potential donors will provide the best chances for long-term graft survival. The types of HLA matches are:
- Perfect match: Finding a perfect match is of course ideal, but only occurs between identical twins.
- Four antigen match: 4-antigen which occurs between some siblings, is next best. There is a 1 in 4 chance that any given sibling pair will match in all 4 of the major (HLA) antigens (there is also a 1 in 4 chance that they will fail to match with any of the HLA antigens). Even when the HLAs match, there are still subtle antigenic differences that are not identified by HLA typing.
- Two antigen match: There is a 1 in 2 chance that any pair of siblings will match in 2 of the HLA antigens. A biological parent (of either gender) is often chosen as the donor for pediatric transplants (usually the mother, for reason of smaller kidney size). Two of the 4 patient’s HLA antigens come from the mother and two from the father. This is what is called a haplotype (2 antigen) match.
- Mismatch: is anticipated if the donor kidney is from a living, unrelated person (spouse, non-first degree relatives) or from a deceased (cadaveric) donor. Mismatched kidneys (grafts) survive much better today that they did a decade or so ago because the newer, more powerful anti-rejection medications partly compensate for the HLA disparity.
2. Whether the kidney is from a living related donor (LRD) or is a cadaveric donation (CD).
Given a similar degree of HLA mismatch, a living donor kidney is always preferable to a cadaveric kidney. The reasons for this are probably the following:
- Ischemia time is generally shorter for a LRD kidney; that is, the time the kidney is without blood perfusion (ischemia time). Perfusing the kidney with special solutions and keeping the kidney cold until it is implanted in the recipient lessen ischemic damage. This can vary from less than an hour to many hours (e.g., if the kidney is shipped from a distant site)
- LRD kidneys are less likely to be injured or damaged, from either ischemia or chronic disease. Living donors undergo an extensive battery of tests to be sure the prospective donor kidney is free of disease/damage (and to be sure that the prospective donor can tolerate removal of one half of the functional units [nephrons]). Conversely, kidneys from deceased donors might have damage from disorders such as hypertension, or nephritis that are unknown to the donor’s family. Few centers routinely biopsy cadaveric kidneys prior to implantation.
3. Additional predictors of long-term graft survival
- Acute rejection episodes: The presence and (frequency) of acute rejection episodes (during the first year post-transplant) is associated with decreased long-term graft survival.
- Serum creatinine concentration (graft function) at one year: impaired graft function at one-year post- transplant predicts reduced long-term graft survival.
- Calcineurin inhibitors: These powerful anti-rejection medications have a down-side, namely, they can cause chronic progressive renal damage. Their use (and the patient’s blood-calcium levels) has to be carefully monitored.
- Recurrence of the original disease in the renal graft: Certain primary disorders (that originally caused the kidney failure) can recur in the renal graft; post-diarrheal hemolytic uremic syndrome rarely does, however.
- Other risk factors: chronic hypertension, high cholesterol, obesity, and diabetes (either type 1 or type 2); in other words, factors associated with poor health in general also reduce graft survival.
Graft survival statistics
Cadaveric kidney graft survival for adult patients (based on 2009, 2005 SRTR National Report and 2002 UNOS report) is:
One year: 91%
Three years: 79%
Five years: 53%
10 years: 51%
Graft survival for children is similar.
Living donor graft survival:
One year: 96%
Three years: 89%
Five years: 81%
10 years: 68%
Again, graft survival in children is similar.
These data are inclusive, and are not stratified according to tissue typing, (i.e., those with closer matching do somewhat better).
Median graft survival (the mid-point; time in years when 50% of grafts are still functioning and 50% are not):
Cadaveric graft: 10 yrs
Living related donor: 15 years