**3. Results**

A total of 2395 kidney transplant recipients were included: 2062 (83.8%) received a 1st kidney transplant, 279 (11.3%) received a 2nd kidney transplant, 46 (1.9%) received a 3rd kidney transplant and 8 (0.3%) received a 4th kidney transplant. The outcomes of the 3rd and 4th kidney transplants were grouped together (3rd+).

Table 1 summarises donor and recipient characteristics. Recipients of 3rd+ kidney transplants were significantly more likely to receive a living donor kidney (*p* < 0.0001).


**Table 1.** Demographics of kidney transplants performed in Northern Ireland in the period 1968–2019.

Donor age, donor sex and cold ischaemic time did not statistically differ between the groups.

In total, 99% of recipients were White. Recipients of repeated kidney transplants were more likely to be male (*p* = 0.006) and were younger (*p* < 0.001): mean age of 1st KTRs was 43.6 ± 16.3 years, versus 39.9 ± 14.4 for 2nd and 41.4 ± 11.5 for 3rd+ KTRs. Furthermore, these patients were also significantly more sensitised, with an increasing cRF from 15% (1st transplant) to 54% (2nd transplant), to 76% (3rd+ transplant) (*p* < 0.0001). As a consequence, there was also an association between multiple kidney transplants and better HLA match at transplantation (*p* < 0.0001). The pre-emptive rate was significantly lower in recipients of multiple transplants (*p* < 0.0001).

## *3.1. Surgical Information*

All kidney transplants were performed extraperitoneally and graft nephrectomy was only performed in four cases: one in relation to uncontrolled antibody mediated rejection with systemic involvement, one following a catastrophic bleed, one simultaneously to the implant and one to create space for a potential 4th graft. The final patient had had multiple gynaecology procedures and the peritoneal content would not have been easily mobilised to allow graft implantation.

Only one major bleeding event occurred that required graft nephrectomy (2nd implant), but the recipient underwent successful implantation of a 3rd graft three years later. Urological complications were not recorded.

#### *3.2. Death-Censored Graft and Recipient Survival*

Figure 1 shows death-censored graft survival, with a median of 328 months for 1st kidney transplant recipients (KTRs) in blue, 209 months for 2nd KTRs in green and 150 months for 3rd+ KTRs in red (*p* = 0.04).

**Figure 1.** Median death-censored graft survival: 328 months for 1st graft (blue line), 209 months for 2nd (green line) and 150 months for 3rd+ (red line). (*p* = 0.04).

Death-censored graft survival remained significantly different between the three groups in the case of deceased donor transplants (Figure 2a), but there was no significant difference in death-censored graft survival between the groups in living donor transplantation (Figure 2b).

**Figure 2.** Difference in death-censored graft survival is seen in deceased donor transplants (**a**) but not in kidneys retrieved from living donors (**b**). Prolonged ischaemia is significantly detrimental to long-term survival in deceased donor grafts and 3rd and 4th transplants are associated with prolonged ischaemic times. These are marginal patients with difficult vasculature—marginal kidneys do less well in this context while good kidneys cope fine. Blue line: recipients of 1st kidney transplant; green line: recipients of 2nd kidney transplant; red line: recipients of 3rd kidney transplant.

Recipient survival was comparable between the three groups (*p* = 0.59), with a median of 234 months for 1st KTRs in blue, 256 months for 2nd KTRs in green and 298 months for 3rd+ KTRs in red (Figure 3). The 10 year recipient survival for all groups exceeded 70%.

**Figure 3.** Median recipient survivals: 234 months for 1st graft (blue line); 256 months for 2nd (green line); 298 months for 3rd+ (red line) (*p* = 0.59).

In multivariate analysis, earlier decade of transplantation, older donor and recipient age, longer ischemic time, and transplant number were significantly associated with death-censored graft loss. Living donor transplantation was associated with improved death-censored graft survival (Table 2).


**Table 2.** Factors associated with death-censored graft survival in all recipients on a multivariate analysis.

Time on RRT and HLA mismatch at HLA-A, - B and -DR were not significant and dropped out of model.

For recipients of 3rd+ transplants, the association with a living donor is the only factor associated with death-censored graft survival (Table 3).


**Table 3.** Multivariate analysis for death-censored graft survival in 3rd+ recipients.

Despite small numbers, a living donor transplant was associated with a 90% reduction in death-censored graft loss.

In multivariate analysis for recipient survival, significant factors were decade of transplant, recipient age, recipient primary disease of diabetic nephropathy, duration of RRT pre-transplant, living donor, donor age and ischaemic time (Table 4).


**Table 4.** Multivariate analysis for recipient survival in all transplants.

HLA mismatch at HLA-A, -B and -DR and transplant number were not significant and dropped out of model.
