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Multifactorial modelling of waiting time
to kidney transplant
UK Transplant
Sibanda N, Johnson RJ, Powis SH
On behalf of the UK Transplant Kidney and Pancreas Advisory Group Access to Transplantation Task Force
Aim Data Methods
• To determine which factors at both the patient and • Adult patients who were listed for a kidney transplant • Patients were followed up for three years from the date of
centre level significantly influence the length of time between the introduction of the revised Kidney listing. Transplant was the end point of interest – any
a patient waits for a transplant after being listed on Allocation Scheme on 1 July 1998 and 30 June 2001. patients who were suspended, removed, died or were still
the kidney transplant list. waiting were censored.
• Patients who received a multi-organ or live donor
• To determine whether there are any statistically transplant were excluded. • Cox regression was used to investigate the influence of the
significant differences in waiting time between factors in a two-stage process:
• For patients who were listed more than once during
centres after adjusting for patient mix and centre
the three-year time period, only the earliest listing • Patient factors only.
level factors.
was included. • Patient and centre factors.
• The resulting cohort had 5,684 patients.
Factors investigated Patient level factors
Results are presented in the Note: The percentages given for each factor level are the unadjusted percentages of patients
Factors investigated
form of hazard ratios. transplanted within three years of listing.
Patient level factor Significant Centre level factor Significant
at 5% level at 5% level
Sensitisation (%PRA) Age at registration
Sensitisation (% PRA) Number of local cadaveric kidney donors A hazard ratio quantifies the 1.2 1.2
Age at registration Average waiting list size relative chance of transplant
1.0 1.0
Minimum match grade requirement Average balance of exchange for a patient with a given level 54% 59%
Matchability points score Offer refusal rate of a factor, compared to a 0.8 0.8
Relative chance
Relative chance
Blood group Number of live donors
patient with the chosen 0.6 41% 0.6
54%
51%
50%
Gender Presence of non-heartbeating donor programme
baseline level of that factor. 33% 28%
41%
HLA-DR homozygosity 0.4 0.4
28%
Number of previous grafts The hazard ratios for one 0.2
0.2
Ethnicity factor are adjusted for the
Residual sensitisation influence of the other factors. 0.0
0-10 11-39 40-59 60-84 85-100
0.0
18-29 30-39 40-49 50-59 ≥60
Primary diagnosis
The chance of transplant declines with Pronounced reduction in the relative chance of
increase in %PRA. transplant for patients listed at age 60 or over
may be explained in part by the increased risk
Centre level factors of removal from or death on the transplant list
for these patients.
Relative chance of transplant for centre level factors Matchability points score Blood group
1.2 4.0
Factor Level No. of Relative chance 95% CI p
centres of transplant 3.5
1.0
Patient-specific score Linear 21 2.58 2.42 – 2.75 <0.0001 56%
3.0
0.8
Number of local cadaveric ≤60 6 0.69 0.56 – 0.84 0.0002
Relative chance
2.5
Relative chance
61%
kidney donors 61–100 8 0.96 0.84 – 1.09 0.5
0.6 2.0
>100 7 1.00
1.5
Mean active waiting list size ≤140 8 1.42 1.21 – 1.65 <.0001 0.4 58%
35%
141 – 200 7 1.24 1.11 – 1.39 0.0001 29% 1.0
46%
>200 6 1.00 0.2 23% 38%
0.5
Mean balance of exchange <0 8 0.49 0.44 – 0.54 <0.0001 0.0 0.0
0 – 12 6 0.60 0.52 – 0.68 <0.0001 1-2 3-4 5-7 8-10 O A B AB
Easy to match Difficult to match
>12 7 1.00
Offer refusal rate (%) <27 7 1.32 1.19 – 1.47 <0.0001
Patients whose tissue type is more difficult to Blood group B patients have a lower chance of
27 – 35 8 1.22 1.10 – 1.35 0.0002
>35 6 1.00 match have a reduced chance of transplant. transplant than patients of other blood groups.
Gender and HLA-DR homozygosity
• Chance of transplant is greater for patients registered at a centre with a larger
1.2 Female patients have a lower chance of
balance of exchange and a larger number of donors.
1.0
transplant compared to male patients. This
52% 53%
• Chance of transplant is lower for patients listed at a centre with higher offer may be explained in part by the significantly
47%
refusal rates and larger transplant lists. 0.8
(p <0.0001) higher proportion of positive
Relative chance
0.6 cross-matches among females (11%) than
• The ratio of the number of waiting list patients to the number of local donors was
among males (7%).
also highly significant (p < 0.0001), and indicated that the chance of transplant 0.4
32%
is considerably poorer for patients registered at centres with a large transplant 0.2
Patients who are homozygous at the HLA-DR
list size relative to their local donor rate. locus have a reduced chance of transplant
0.0
Male Female No Yes compared to those who are heterozygous.
Gender HLA-DR homozygous
Centre differences Number of previous grafts Ethnicity
1.2 1.4
Relative chance of transplant after adjusting for patient and centre
level factors 1.0
1.2
21 53%
20
1.0
19 52%
18 While centre differences 0.8
Relative chance
Relative chance
17
0.8
16
15
were much reduced after 0.6
14
13 adjusting for patient and 38% 0.6 36% 46%
12 *p<0.0001 0.4
Centre no.
p* < 0.0001
11
10
centre level factors, there 0.4 36%
26%
9
8
remained statistically 0.2
0.2
7
6 significant (p<0.0001) 0.0 0.0
5
≥2
4
3
differences in the chance of 0 1 White Asian Black Other
2
1
transplant across centres.
0
0.0 0.5 1.0 1.5 2.0 2.5 3.0 The chance of transplant declines as the Asian, Black and other minority ethnic patients
Relative chance of transplant
*p-value for testing hypothesis of no significant differences across centres in the chance of transplant within three years of registration after
number of previous grafts increases. have a reduced chance of transplant compared
adjusting for patient and centre level factors
to White patients.
Summary
• The chance of transplant declines as the level of sensitisation (%PRA), the matchability • There is an increased chance of transplant for patients registered at centres with a higher
points score, the number of previous grafts and the age at registration all increase. balance of exchange and a larger number of deceased adult donors.
• Blood group B patients have a reduced chance of transplant compared to other blood • There are reduced chances of transplant for patients registered at centres with higher
groups and female patients have a lower chance of transplant than male patients. offer refusal rates and larger waiting lists. The chance of transplant declines as the
number of waiting list patients relative to the number of local cadaveric donors increases.
• Asian, Black and other ethnic minority patients have a reduced chance of transplant
compared to White patients and patients who are homozygous at the HLA-DR locus have • There were statistically significant differences in the chance of transplant across centres
a reduced chance of transplant compared to those who are heterozygous. after adjusting for the patient and centre level factors investigated.
