Kidney transplantation is a recognised and efficacious method of renal replacement therapy in patients with end-stage renal disease (ESRD), cheaper than dialysis therapy and allowing for longer survival. As Wolfe et al. (1) (1999) demonstrated in their classical study, the survival time of kidney transplant recipients is longer than that of dialysed patients or those dialysed and placed on the list of patients awaiting transplantation. However, at the time of publication only 1% of Americans aged over 70 years received a kidney from a dead donor; in addition, advanced age has always been a factor negatively affecting participation of the patients in clinical trials.

Over the last 20 years the demographic situation in the world, including Poland, has changed. According to Polish statistical data, in 2030 people over 65 years of age will constitute ca. 24% of the society; the number of elderly patients with chronic renal disease is also increasing, due to longer life as well as concomitant diseases such as diabetes mellitus and arterial hypertension which, if poorly controlled, affect kidney function. Aging of the society results in older recipients as well as donors – due to the widespread shortage of organs.

According to the “Poltransplant” bulletin (2), by the end of the year 2011 the National Waiting List included 2623 individuals awaiting kidney transplant, including 453 patients aged over 60 years (for the comparison: in 2008 there were 192 patients in this age group); despite a stable number of newly added patients, the number of awaiting elderly patients grew significantly, which also increased the mean age of patients awaiting kidney transplant – 47 years and 3 months at present. The Polish system of kidney allocation for recipients placed on the waiting list is based on medical criteria and functions in accordance with the regulation of the Minister of Health of December 4th, 2009, concerning the national list of patients awaiting transplantation. One criterion of preferential donor-recipient matching is transplantation of a kidney obtained from a donor more than 65 years old to a recipient over 60 years of age (so-called obligatory transplantation, regardless of the score including HLA compatibility, duration of dialysis therapy, the need of retransplantation, and other factors). Such a system for allocation of “old” kidneys is consistent with the European Senior Program (ESP) introduced by Eurotransplant on 1.01.1999 (3). The aim of this program was to increase the number of kidneys obtained from elderly donors and shorten the time of waiting for transplantation for elderly recipients without a negative effect on the organ’s or patient’s survival. In order to shorten the cold ischaemia time and minimise the related risk of ischaemic damage, “old-for-old” transplantations may be possible within local waiting lists; the compatibility of main blood groups is mandatory and the PRA (panel-reactive antibody) value must be less than 5%, while HLA compatibility is not taken into account in the program. Initially the member states of Eurotransplant entered the program voluntarily; after two years the system became mandatory as a part of the European Kidney Allocation System (ETKAS).

A patient awaiting kidney transplant has a chance to receive an organ from a living donor, a deceased donor below 65 years of age, or a deceased donor over 65 years old. In 2011 in Poland 1002 recipients received kidneys from deceased donors, while only 40 patients were transplanted with a kidney from a living donor; therefore, elderly recipients have virtually no chance of receiving a kidney from a living donor. The possibility of discontinuation of dialysis therapy is mainly associated with the “old-for-old” principle, as kidneys from young donors are seldom transplanted to elderly recipients. It must be remembered that the aim of kidney transplantation in a young person is to allow for long-time survival of the patient (and the transplanted organ) and, should the organ cease to function, for retransplantation. A geriatric recipient’s chance for retransplantation is low and the aim of transplantation is to prolong life and increase its quality in comparison with that of a peer on lifetime dialysis.

Kidney transplantation in the elderly is associated with the term “marginal donor”, introduced as early as in 1991, (4) changed in 2002 to “expanded-criteria donor” (ECD) (5, 6): a deceased donor over 60 years of age without concomitant diseases or a deceased donor 50-59 years old meeting at least 2 out of 3 criteria: creatinine concentration over 1.5 mg/dl at the time of death, cerebrovascular death, or a history of arterial hypertension. As a rule, transplantation of a kidney from an ECD is associated with a 70% higher risk of graft failure in comparison with transplantation from a standard-criteria donor (SCD).

What is the difference between a kidney of an older donor and a younger kidney? The process of ageing affects all organs, including the kidneys (7-9). The weight of a kidney, increasing from birth to ca. 400 g in the 5th decade of life, then continuously falls by ca. 20-30% up to the age of 80 years. This affects in particular the cortical layer, with thinning and changed echostructure (due to scarring secondary to vascular lesions). Lesions typical for the ageing kidney are similar to those observed in other organs: arteriolosclerosis (accumulation of hyaline deposits), fibroblastic hypertrophy of the intima and media of the arcuate arteries and arterioles, and thickening of the basal membrane. Secondary to vascular lesions focal glomerulosclerosis, atrophy of the tubules (mainly proximal), and interstitial fibrosis (mainly in the cortex) develop. Arteriosclerosis is also observed and high pulse waves inflict additional damage on the walls of small vessels. The number of the glomeruli decreases with age (from a mean of 1 million per kidney) by 30-50%, with an increased proportion of “physiologically” sclerotic glomeruli, resulting in compensative hypertrophy and hyperfiltration of the medullar glomeruli, with their secondary segmental and global sclerosis.

The Poltransplant data indicate that in the years 2006-2011 the most common cause of death of donors in Poland were cerebrovascular conditions, i.e. haemorrhagic or ischaemic stroke (59%), and the mean age of a dead donor in 2011 was over 44 years; therefore, transplantation of organs from dead ECDs, mainly to elderly recipients, is a fact and the personnel involved in the process of donor preparation and the operation should minimise the negative effects of the donor’s age and health on the recipient’s prognosis.

Provided that the probability of the organ being obtained from an ECD increases with the donor’s age (10, 11) and the possibility of transplantation of a kidney from a living donor whose organ – even if not young – is still of better quality than that of a deceased donor (12) is very small, the quality of an “old” kidney becomes very important. Age-related physiological changes in the kidneys combined with the donor’s past diseases, the risk of ischaemic injury, and potential nephrotoxicity of immunosuppressive medications result in the risk of primary graft insufficiency (13). The mechanism of this injury is unclear, although ageing seems to limit the repairing properties of epithelial cells. The number of glomeruli without tubules also increases, as demonstrated in patients with chronic allograft nephropathy (14). Therefore, the correlation of the donor’s age and the cold ischaemia time becomes critical for the recipient’s prognosis. Is it possible to “predict” lower quality of an elderly kidney before transplantation if, as demonstrated by the Third National Health and Nutrition Survey (NHANES III) performed in the USA, only in 7.6% of individuals 60-69 years old and in 25.9% of those aged over 75 years eGFR is below 60 mlmin/1.73 m² (15)? Preimplantation kidney biopsy is not a new idea (16) – histological assessment of the organ may facilitate the decision to reject an organ or the choice between single and dual kidney transplantation (SKT vs. DKT) in order to increase the final eGFR value. Remuzzi et al.(17) assessed kidney biopsy specimens obtained from potential donors aged over 60 years using a scale concerning specific features (in which 0 represented no abnormalities and 12 – advanced interstitial lesions): kidneys scoring 0-3 were used for single transplantations, those scoring 4-6 – for dual transplantations, and the remaining organs were rejected. After 3 years of follow-up the results of DKT were better than those of SKT for elderly donors. Another “cut-off” parameter may be the number of sclerotic glomeruli. Andres et al. (18) evaluated kidneys obtained from donors aged 60-75 years and performed SKT if the proportion of sclerotic glomeruli was lower than 15% and DKT if the proportion was 15-50%. After a year the kidney survival rate was 90% in the SKT group and 95% in the DKT group.

In Poland in 2011 the DKT procedure was applied in 4 recipients.

On the margin of this review the study by Kasiske and Snyder (19) should be recalled. The authors demonstrated that the prognosis is determined not by the recipient’s age but the donor’s age – the results of “old-for-old” transplantations were better than “old-for-young”.