Wait list status of pediatric dialysis patientsin North America

In children, kidney transplantation is associatedwith improved patient survival, growth, andquality of life when compared to chronic dialysis(1–3). Furthermore, waiting time on dialysis is aknown independent predictor for poor long-termpatient and graft survival among adults andadolescents (4–7). Recognizing the benefits ofprompt renal transplantation in pediatric end-stage renal disease patients, the deceased donorkidney allocation policies in the United Stateshave long given priority to pediatric patients.Although living-related donation is common

in pediatric kidney transplantation, historicallynearly half of the pediatric transplant recipientsin the United States receive their kidneys fromdeceased donors (8). Therefore, prompt registra-tion on the wait list for kidney transplantation isimportant to facilitate early kidney transplanta-tion. However, there are groups who are known

to have unequal rates of registration on thetransplant wait list. Female dialysis patients andblack dialysis patients are less likely to be on thekidney transplant wait list when compared tomale dialysis patients and white dialysis patients(9–11). Even among adolescent dialysis patientswho have low rates of comorbid conditions thatpreclude renal transplantation, unequal rates ofwait list registration for girls and black pediatricdialysis patients exist. These disparities to waitlist registration persisted despite adjustment forage, underlying diagnosis, or socioeconomicstatus.Previous studies could not examine whether

family preference or ongoing medical reasonsexplained the unequal wait list registration forkidney transplantation among pediatric patients.Little is known on how family preferencestoward kidney transplantation may differ by sexor race. Secondly, physician beliefs regardingmedical readiness have not been directly mea-sured as a reason for not being registered on thekidney transplant wait list. Finally, familypreferences and medical reasons for kidney

Nguyen S, Martz K, Stablein D, Neu A. Wait list status of pediatricdialysis patients in North America.PediatrTransplantation2011:15:376–383.�2011JohnWiley&SonsA/S.

Abstract: Kidney transplantation is the treatment of choice for themajority of pediatric patients with end-stage kidney disease. Previousstudies demonstrating racial or gender disparities in access to the de-ceased donor transplant list could not evaluate the impact of medicalconcerns or patient preference on waitlist status. We undertook a ret-rospective cohort study using the NAPRTCS registry to begin todetermine barriers to wait list registration for kidney transplantationamong pediatric dialysis patients. Clinical and demographic factorswere compared in listed vs. non-listed patients. Reasons cited for notlisting patients were examined by clinical and demographic factors. Atdialysis initiation, 88.7% of pediatric dialysis patients were not on therenal transplant wait list. Twelve months after dialysis initiation, 67.1%of pediatric dialysis patients were not on the wait list. The groups leastlikely to be on the wait list were infants (adjusted OR 0.23, 95% CI 0.16,0.32) and girls (adjusted OR 0.78, 95% CI 0.67, 0.90) after adjusting formultiple confounders. The reason most often cited for not listing wasmedical reason for young infants and that the transplant workup waspending for girls. Further study is needed to identify barriers to wait listregistration.

Stephanie Nguyen1, Karen Martz2,Don Stablein2 and Alicia Neu3

1University of California, Davis, Sacramento, CA, 2TheEMMES Corporation, Rockville, MD, 3The JohnsHopkins University School of Medicine, Baltimore,MD, USA

Key words: kidney transplantation – wait list –children – adolescent

Stephanie Nguyen, MD, MAS, University ofCalifornia, Davis, 2516 Stockton Blvd., Sacramento,CA 95817, USATel.: 916 734 8118Fax: 916 734 0629E-mail: stephanie.nguyen@ucdmc.ucdavis.eduFunding source: none.

Accepted for publication 19 January 2011

Abbreviations: FSGS, focal segmental glomerulosclerosis;GEE, generalized estimating equation; NAPRTCS, NorthAmerican Pediatric Renal Trials and Collaborative Studies.

Pediatr Transplantation 2011: 15: 376–383 � 2011 John Wiley & Sons A/S.

Pediatric TransplantationDOI: 10.1111/j.1399-3046.2011.01495.x

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transplantation may have altered over timebecause of changes in immunosuppression andimprovements in outcome for deceased donorkidney transplantation.To begin to identify factors that influence wait

list status for kidney transplantation in children,we evaluated which demographic or clinicalfactors predict registration on the wait list andwhether registration on the wait list has changedover time. Furthermore, we evaluated whetherfamily preference or medical reasons may explainthe differences to registration on the kidneytransplant wait list.

Materials and methods

Study design

We conducted a retrospective registry-wide study of allpediatric patients (age <21 yr) who initiated maintenancedialysis after January 1, 1992 and whose data were enteredin the NAPRTCS Dialysis registry. NAPRTCS is a volun-tary collaborative effort of 150 pediatric renal treatmentcenters in the United States, Canada, Mexico, and CostaRica. The registry records information at 30 days afterdialysis initiation, six months post-dialysis initiation, andevery six months thereafter. Permission for participation inthe NAPRTCS registry was obtained through the Institu-tional Review Board at each participating center.Patient information was reported by the referring center

and included age at time of dialysis initiation, sex, race/ethnicity (white, black, Hispanic, or Other), underlyingdiagnosis (obstructive uropathy, FSGS, renal dysplasia,reflux nephropathy, or other), and dialysis modality (peri-toneal dialysis or hemodialysis). Patients were divided intothree cohorts by year of dialysis initiation: 1992–1996, 1997–2001, and 2002–2005. Transplant center volume was calcu-lated based on the total number of patients in the NAP-RTCS transplant registry for each center divided by thenumber of years the centered entered at least one patient.Centers without any transplant patients were excluded.Transplant center volume was not normally distributed, andtherefore, we divided the category by quartiles. High-vol-ume transplant centers were defined as those centers in theupper 75th percentile and had >6.76 transplants per yearwhile low-volume transplant centers were defined as thosecenters in the lower 25th percentile and had <2.25 trans-plants per year.Wait list status was categorized as either listed or not-

listed and was determined by the referring center. For thosepatients not listed on the kidney transplant wait list, refer-ring centers further categorized the reason why the patientwas not listed as either transplant pending (preparation/workup in progress), medical reasons, or family/patientpreference.

Statistical analysis

Descriptive statistics were employed for each clinical anddemographic factor. A cross-sectional analysis was used tocompare clinical and demographic factors in listed andnot-listed patients by chi-square test at the time of dialysisinitiation, six, and 12 months. Logistic regression analysiswas used to evaluate significant demographic or clinical

predictors for being registered on the wait list at dialysisinitiation, six, and 12 months. The multivariate modelsimultaneously adjusted for age, sex, race/ethnicity, under-lying diagnosis, dialysis modality, cohort group, and centervolume. A GEE analysis with a binomial distribution and alogit link was used to analyze clinical and demographicfactors related to wait list status with time added as arepeated measure within patients. In all models, patientswere excluded if they had incomplete data, received a kidneytransplant, died, or had a return of kidney function. Allmodels included fixed variables measured at dialysis initi-ation. p < 0.05 is considered statistically significant. Allanalyses performed used sas statistical software (SASInstitute, Cary, NC, USA).We performed sensitivity analysis by recategorizing pa-

tients who are ‘‘not on list, transplant preparation,’’ to beincluded in the outcome of wait listed as centers may haveinterpreted ‘‘transplant pending’’ to include those who areawaiting a living donor transplant or are on the wait list butare inactive for transplant (‘‘list and hold’’). We preformedthe same analysis to include this new outcome category toevaluate whether it altered our results.

Results

Patient population and characteristics

There were 4473 patients entered after January 1,1992 in NAPRTCS for their first course ofmaintenance dialysis. At the time of registration,boys made up 54.9% of the dialysis patients andpatients older than 13 yr were the largest agegroup (44.8%). There were 48.5%, 24.1%,20.3%, and 7.1% of white, black, Hispanic,and Other races, respectively, represented at thetime of dialysis registration. There were morepatients in the earliest cohort group 1992–1996(n = 1973) and 1997–2001 (n = 1705) vs. in thelatest cohort 2002–2005 cohort group (n = 795).An underlying diagnosis was because of obstruc-tive uropathy 12.7%, FSGS 14.6%, renal dys-plasia 14.4%, reflux nephropathy 3.6%, other46.7%, and missing 8%. Peritoneal dialysis wasthe modality at dialysis initiation in 65.7% ofpediatric patients. At dialysis initiation, 7.6%,42.1%, and 50.3% of pediatric dialysis patientswere at low-, medium-, and high-volume trans-plant centers, respectively. The number patientsexcluded for missing data and lost to follow-upwere 135 (3%), 550 (12.3%), and 852 (19%) atdialysis registration, six, and 12 months afterdialysis initiation, respectively.

Wait list status by clinical and demographic characteristics

Wait list status was known for 97% of dialysispatients at the time of dialysis initiation. Afterexcluding patients with missing data, 11.3%,19.4%, and 20.3% of dialysis patients were onthe wait list for kidney transplantation at thetime of dialysis initiation, six, and 12 months of

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follow-up, respectively (Fig. 1). After 12 monthsof follow-up, more dialysis patients were on thewait list for a kidney transplant than at dialysisinitiation (20.3% vs. 11.3%). At any point oftime, the most common reason cited for notbeing on the wait list was that transplant waspending.In the unadjusted analysis, the youngest age

group, 0–1 yr, had the lowest percentage ofpatients on the wait list at every time point (datanot shown). A lower percentage of girls thanboys were on the wait list at dialysis initiationand at six months (9.9% vs. 12.5%, p = 0.007,21.6% vs. 25.9%, p = 0.005, respectively).Patients of Other race were more frequently onthe wait list than white, black, or Hispanicpatients at every point in time. Patients withreflux nephropathy were more frequently on thewait list than those with other underlying diag-noses at dialysis initiation and at six months.Patients on hemodialysis and peritoneal dialysiswere equally prevalent on the wait list at dialysisinitiation; however, after six and 12 months offollow-up, peritoneal dialysis patients were morefrequently on the wait list than hemodialysispatients. Dialysis patients in high-volume trans-plant center were more often on the wait list thandialysis patients in lower-volume transplant cen-ters at dialysis initiation and at six months. Morepatients in the earliest cohort group (1992–1996)

were on the wait list when compared to the twolater cohort groups (1997–2001 and 2002–2005).In the logistic regression analysis adjusted for

cohort group, age, race/ethnicity, sex, underlyingdiagnosis, dialysis modality, and center trans-plant volume, the youngest age group, 0–1 yr,was the least likely age group to be placed on thewait list at dialysis initiation (adjusted OR 0.18;95% CI 0.10, 0.31), at six months (adjusted OR0.22; 95% CI 0.15, 0.33), and at 12 months(adjusted OR 0.28; 0.19, 0.40) (Table 1). Girlswere less likely than boys to be on the wait list atdialysis initiation (adjusted OR 0.74; 95% CI0.60, 0.92), at six months (adjusted OR 0.77;95% CI 0.65, 0.93), and at 12 months (adjustedOR 0.81; 95% CI 0.67, 0.98). Patients of Otherrace were more likely than white patients to be onthe wait list at dialysis initiation (adjusted OR1.66; 95% CI 1.17, 2.37), at six months (adjustedOR1.68; 95% CI 1.23, 2.31), and at 12 months(adjusted OR1.67; 95% CI 1.18, 2.37). Blackpatients were more likely than white patients tobe placed on the wait list at dialysis initiation(adjusted OR 1.33; 95%CI 1.04, 1.69) but not forany subsequent time period. Hispanic patientswere more likely than white patients to be placedon the wait list at 12 months of follow-up(adjusted OR 1.36; 95% CI 1.05, 1.76) but notfor any time period prior. Patients receivingperitoneal dialysis were more likely than patientsreceiving hemodialysis to be placed on the wait

11.3%19.4% 20.3% 18.0%

43.3%

27.9%

15.5%

24.4%

36.1%

9.3%

9.3%

7.8%

34.5%

16.6%

0%

10%

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50%

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70%

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90%

100%

Listed Not listed Transplant Listed Not listed Transplant Listed Not listed Transplant

Not listed: transplant pending Not listed: medical reasons Not listed: family choice

Dialysis initiation 6 Months 12 Months

Fig. 1. Renal transplant and wait list status of pediatric dialysis patients in NAPRTCS at dialysis initiation, six, and12 months of follow-up. At six months, 1.5% of subjects had return of kidney function and 0.8% died. At 12 months, 2.5%of subjects had return of kidney function and 1.5% died. Dialysis patients with missing data were excluded.

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list at dialysis initiation (adjusted OR 1.30; 95%CI 1.05, 1.61) but not at six or 12 months. Theunderlying diagnosis was significant predictor forbeing on the wait list at registration (overallp = 0.03) and at six months (overall p = 0.01),but not at 12 months (overall p = 0.91). How-ever, within our classification of underlyingdiagnoses, no individual underlying diagnosiswas a significant predictor for registration on thewait list. The later cohort group was less likely tobe on the wait list than dialysis patients from theearliest cohort; however, this was only statisti-cally significant at six months of follow-up(overall p = 0.006). Dialysis patients at high-volume transplant centers were more likely to beon the wait list at dialysis initiation (adjusted OR1.54; 95% CI 1.25, 1.90) than dialysis patients inlower-volume centers.

In the repeated-measures analysis with time asan added variable, the youngest group, 0–1 yr,remained the least likely group to be placed onthe wait list (adjusted OR 0.23, 95% CI 0.16,0.32) (Table 1). Girls remained less likely thanboys to be on the wait list (adjusted OR 0.78,95% CI 0.67, 0.90). Black patients and patientsof Other race were more likely than whitepatients to be placed on the wait list. Therewas a trend that later cohort groups were lesslikely to be on the wait list registration than theearlier 1992–1996 cohort group (overallp = 0.053). Primary diagnosis, dialysis modal-ity, and center volume were not significantpredictors for wait list registration when adjustedfor time of follow-up. Follow-up time afterdialysis initiation was a significant predictor forwait list registration.

Table 1. Adjusted OR for registration on the renal transplant wait list at dialysis initiation, 6, 12 months, and at any time during follow-up

OR (95% CI)

Dialysis Initiation* 6 months* 12 months* At any time�

Cohort group1992–1996 Reference1997–2001 0.84 (0.68–1.05) 0.79 (0.65–0.95) 0.89 (0.72–1.09) 0.83 (0.71–0.98)2002–2005 1.00 (0.76–1.32) 0.72 (0.56–0.93) 0.84 (0.64–1.11) 0.84 (0.68–1.03)

Age at registration0–1 0.18 (0.10–0.31) 0.22 (0.15–0.33) 0.28 (0.19–0.40) 0.23 (0.16–0.32)2–5 0.87 (0.61–1.23) 0.83 (0.61–1.13) 0.97 (0.69–1.36) 0.88 (0.68–1.13)6–12 Reference13+ 1.21 (0.97– 1.51) 1.10 (0.90–1.34) 1.19 (0.96–1.48) 1.16 (0.98–1.36)

Race/ethnicityWhite ReferenceBlack 1.33 (1.04–1.69) 1.16 (0.93–1.44) 1.21 (0.96–1.53) 1.22 (1.03–1.46)Hispanic 0.86 (0.64–1.16) 0.91 (0.71–1.17) 1.36 (1.05–1.76) 1.04 (0.85–1.27)Other 1.66 (1.17–2.37) 1.68 (1.23–2.31) 1.67 (1.18–2.37) 1.67 (1.28–2.20)

SexBoy ReferenceGirl 0.74 (0.60–0.92) 0.77 (0.65–0.93) 0.81 (0.67–0.98) 0.78 (0.67–0.90)

Underlying diagnosisObstructive uropathy ReferenceFSGS 0.90 (0.63–1.29) 0.88 (0.64–1.20) 1.16 (0.81–1.66) 0.97 (0.74–1.26)Renal dysplasia 1.13 (0.78–1.63) 1.07 (0.78–1.47) 1.18 (0.82–1.69) 1.12 (0.85–1.47)Reflux nephropathy 1.58 (0.96–2.61) 1.17 (0.73–1.89) 1.12 (0.65–1.94) 1.28 (0.85–1.93)Other 0.86 (0.63–1.16) 0.74 (0.56–0.97) 1.15 (0.85–1.56) 0.89 (0.71–1.12)

Dialysis modalityHemodialysis ReferencePeritoneal dialysis 1.30 (1.05–1.61) 0.85 (0.71–1.03) 1.00 (0.82–1.23) 1.01 (0.87–1.18)

Transplant centerLow volume 0.90 (0.58–1.39) 1.16 (0.83–1.62) 0.91 (0.64–1.29) 1.00 (0.75–1.33)Medium volume ReferenceHigh volume 1.54 (1.25–1.90) 1.19 (0.99–1.42) 0.90 (0.74–1.09) 1.16 (1.00–1.35)

TimeInitiation of dialysis Reference6 months 2.52 (2.29–2.79)12 months 3.96 (3.52–4.45)

*Multivariate logistic regression model. Model simultaneously adjusted for cohort group, age, race/ethnicity, sex, underlying diagnosis, dialysis modality, and centertransplant volume.�Generalized estimating equation model. Model simultaneously adjusted for cohort group, age, race/ethnicity, sex, underlying diagnosis, dialysis modality, andcenter transplant volume with time of follow-up included as a repeated measure.

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Reasons for not listing by clinical and demographiccharacteristics

At 12 months, 67.1% of dialysis registry patientsremaining on dialysis were not on the wait list fora kidney transplant. While in the infant agegroup, 0–1 yr, medical reason was the most oftencited cause for not being on the wait list at everypoint in time (Fig. 2), in the older age groups,transplant pending was the most often citedcause for not being on the wait list at every pointin time. For boys and girls, transplant pendingwas the most often cited cause for not being onthe wait list at every point in time (Fig. 3).Family choice was cited as the cause for notlisting in approximately 12.7% of patients still ondialysis at 12 months, excluding those who hadreceived a renal transplant. There was no differ-ence in the percentage of patients not listed forfamily choice by gender or race. However, theprevalence of children not listed owing to familychoice still on dialysis at 12 months increased ineach age group.

Sensitivity analysis

When the end point was revised to includepatients not listed – transplant pending, therewere 54.6%, 58.4%, and 62.2% on the wait list atdialysis initiation, six, and 12 months. Infants, 0–1 yr, remained the least likely age group to be onthe wait list at dialysis initiation, six, and12 months adjusted for cohort group, age, race/ethnicity, sex, underlying diagnosis, dialysismodality, center transplant volume, and time offollow-up. Girls were less likely than boys to beon the wait list at dialysis initiation, six, and12 months adjusted for cohort group, age, race/ethnicity, sex, underlying diagnosis, dialysismodality, center transplant volume, and time offollow-up; however, this did not reach the level ofstatistical significance.

Discussion

Graft and patient survival for deceased donorkidney transplantation have steadily improvedand now approach those of living donor kidneytransplantation (12). With recent changes in theUNO�s allocation policies, an increasing numberof pediatric kidney transplants have been per-formed using deceased donors (13). Thus,prompt placement on the deceased donor waitlist is an important component of the care ofdialysis patients and some experts have recom-mended that access to transplantation shouldbecome a measure of quality of care for dialysiscenters (14).

However, there may be several factors thatmay justify a delay in placing patients on thekidney wait list, including medical issues, patientor family preference, or the availability of livingdonors. Although studies documenting racialand gender biases in time to waitlisting amongdialysis patients have sought to identify some ofthese issues, none have been able to directlyevaluate the reason for not-waitlisting patients.In this study, not only were we able to determineclinical and demographic factors associated withnot being placed on the kidney transplant waitlist, but because NAPRTCS queries centersabout the reason for not waitlisting, we wereable to begin to evaluate whether the reasons fornot waitlisting varied among the various patientgroups.Perhaps not surprisingly, we found that

nearly 90% of children are not on the renaltransplant wait list at dialysis initiation. Amongthose patients who remain on dialysis for12 months, two-thirds are not on the wait list.Interestingly, the earliest cohort of dialysispatients (1992–1996) was 17% and 16% morelikely to be on the wait list than later groups(1997–2001 and 2002–2005, respectively). It ispossible that the changes in UNO�s policies thatprovide preference to pediatric patients haveremoved one of the major incentives for promptplacement on the wait list, as time on the waitlist is no longer the primary determinant oforgan availability for pediatric patients. Anotherpossible explanation is that later cohort groupsmay be enriched with children who present latewith advanced kidney disease as children withslowly progressive disease would have received apre-emptive kidney transplant (transplantationwithout prior initiation of chronic dialysis).However, data from NAPRTCS do not supportan increase in the number of pre-emptivetransplants performed in the later cohort groups(15).In all time periods, infants were the least likely

age group to be on the wait list for kidneytransplantation and likely reflect the impact ofearly reports from NAPRTCS which suggestedthat transplant patient survival for infants wasparticularly poor (16). However, recent reportsshow improvement of infant survival on dialysis(17) and transplant outcomes (12, 18), and thus,this trend may change in the future. In support ofthis notion is that the most common barrier citedto being on the wait list for young infants wasmedical reason. Centers may wait for infants tomeet the appropriate size requirements beforethey are placed on the wait list. Very few centerscited family preference as a reason this age group

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was not on the wait list. There may be someselection bias as families of infants who chose notto be on the transplant wait list would also be lesslikely to start chronic dialysis and therefore notbe included in this analysis.

Girls are less likely than boys to be on thetransplant wait list even after adjusting formultiple confounders such as age, race/ethnicity,underlying diagnosis, and time of follow-up.Transplant pending (transplant preparation/

24.7%

48.7% 49.3% 43.4%

68.3%32.8% 29.2%

32.0%

4.5%

7.8% 9.7% 10.8%

10.7% 11.8% 13.9%2.6%

0%

10%

20%

30%

40%

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0–1 yr. 2–5 yr. 6–12 yr. 13+ yr.a. Dialysis initiation

27.9%40.9% 37.0% 33.4%

58.8%26.3%

24.4% 25.8%

6.1%

10.5%12.2% 12.8%

7.2%22.3% 26.5% 28.0%

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

0–1 yr. 2–5 yr. 6–12 yr. 13+ yr.

b. 6 months

39.6%32.8% 29.0% 25.3%

42.0%

23.0%22.8%

21.6%

6.0%

10.8% 13.8%14.5%

12.4%

33.3% 34.4% 38.6%

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

0–1 yr. 2–5 yr. 6–12 yr. 13+ yr.

Not listed: transplant pending Not listed: medical reasonsNot listed: family choice Listed

c. 12 months

Fig. 2. Cited reasons patient isnot on the transplant wait list at(a) dialysis initiation, (b) sixmonths, and (c) 12 monthsstratified by age group.

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workup in progress) was the most often citedreason why girls were not on the wait list at everypoint in time. Interestingly, previous adult datashow that women are less likely to complete thetransplant evaluation process and may explainwhy women are less likely than men to betransplanted (9). Unfortunately, girls are lesslikely to have a living-related donor than boys(19) and girls have fewer pre-emptive transplantsthan boys (20). Even though our analysis tries tocontrol for underlying disease, there may still beresidual confounding. Girls will more frequentlyhave underlying diseases like lupus where thesudden acuity could preclude enough time tocomplete the transplant workup prior to startingdialysis. That is, although medical reasons maynot prevent girls from being evaluated fortransplant, they could slow the transplant eval-uation process once initiated. However, wecannot also exclude other barriers such as pro-vider bias. A prior study in adults shows thatracial and gender disparities in the transplantevaluation process may disappear if all trans-plant candidates were actively solicited (21).Unlike prior studies, we observed that black

pediatric dialysis patients were more likely to beregistered on the wait list than white pediatricdialysis patients (9, 10). This may be partlyexplained by the fact that white patients havemore pre-emptive kidney transplants than blackpatients (18). However, it is very encouragingthat black pediatric dialysis patients are morelikely to be on the wait list for a renal transplantthan white pediatric dialysis patients becauseblack patients are also more likely to receive adeceased donor renal transplant (22).Limitations of the present study include the

voluntary nature of the NAPRTCS registry and

an incomplete ascertainment of cases and out-comes. The NAPRTCS registry only includespediatric dialysis centers. One-third of dialysispatients, mainly older adolescents, obtain care inadult dialysis centers (23). Although wait liststatus of these patients has never been reported,adults in for-profit dialysis centers are less likelyto be on the transplant wait list than dialysispatients in not-for-profit dialysis centers (24). Inour data set, 95% of NAPRTCS centers that carefor pediatric dialysis patients also have trans-plant capabilities and thus presumably havefewer barriers to referral for renal transplanta-tion. Secondly, this data set does not include pre-emptive renal transplants. We have previouslyalluded to how this may affected some of ourresults. In general, we would presume our dataset of children who started dialysis prior totransplant would be enriched with children whoare medically less stable, a shorter presentationof illness prior to requiring renal replacementtherapy, and have less social or familial re-sources.We recognize that each center may interpret

‘‘listed’’ differently, and this is a significantlimitation of the study. Centers may have inter-preted being ‘‘listed’’ as being placed on the waitlist and active for transplant. In this case,patients who are on the wait list but are inactivefor transplant (‘‘list and hold’’) may be misclas-sified as ‘‘not listed.’’ When the end-point wasrevised to account for this potential misclassifi-cation, it continued to reveal that infants wereless likely to be waitlisted. Girls also continued tobe less likely to be on the wait list, although thedifference did not reach statistical significance. Inaddition, misclassification is likely to produce anon-differential bias, that is, misclassification of

42.0% 44.8%33.1% 36.1%

29.7% 28.7%

36.1%36.1%

30.0%30.4%

24.3% 26.1%

9.2%

11.0%12.0%

12.0% 13.6%

12.5% 9.9%

25.9% 21.6%34.0% 31.6%9.3%

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

Boys Girls Boys Girls Boys Girls

Not listed: transplant pending Not listed: medical reasonsNot listed family choice Listed

Dialysis initiation 6 months 12 months Fig. 3. Prevalence of cited rea-sons patient is not on the trans-plant wait list stratified by sexand time on dialysis.

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listing status should be the same whether thepatient is a girl, boy, adolescent or infant.Similarly, transplant pending may include thosepatients listed but pending completion of trans-plant as well as patients whose transplant eval-uation is pending. Another significant limitationis the lack of detail provided in the currentlyavailable options for ‘‘reasons for not-listing’’ inthe NAPRTCS registry. It is recognized that thecurrent classification leaves many unansweredquestions. Despite these problems, this study isstill the largest pediatric study to evaluate thestatus of pediatric dialysis patients on the trans-plant wait list and begins the process of identi-fying and addressing barriers to transplantation.In summary, our results indicate that girls, in

particular, were less likely to be registered on thetransplant waiting list, which could not beexplained by medical reasons or family prefer-ence. Black race was associated with an increasedlikelihood of being placed on the transplant list.That a transplant was pending was the mostcommon reason for most patients not beingplaced on the wait list and, except for theyoungest patients, medical reasons and familypreference did not appear to be significantbarriers to waitlisting. Future studies to furtherclarify the potential barriers to both living anddeceased donor kidney transplantation are re-quired. Specifically, future studies should addresscenter practice variations for waitlisting pediatricpatients and how medical complications maydelay transplantation.

Acknowledgments

We thank the North American Pediatric Renal Trials andCollaborative Studies for supporting this special analysis.

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