The kidney transplant waiting list maintained by the UNOS gets longer every year as does the average waiting time for patients on the list. This is true even though the number of patients diagnosed with end-stage renal disease (ESRD) has declined slightly over the past few years. What is driving this? To examine this problem, I examined the data for annual changes in the number of patients with ESRD and the number on the waiting list.

About the data

The data for annual incidence (number of new cases of ESRD diagnosed in a year) and prevalence (total number of people with ESRD at the end of each year) were obtained from the USRDS 2009 annual report. The report contains a wealth of data on chronic kidney disease and ESRD. It has an entire chapter devoted to transplantation.

The data on the UNOS waiting list data was obtained from the UNOS. Some is available from OPTN annual reports or from the report builder web service. Others were generated specifically for me by UNOS. I want to thank Katarina Linden of UNOS for summarizing the SAS data used in this blog post. Any errors in analysis are mine alone.

A few notes regarding the UNOS data. First, the data being analyzed is for the kidney-only list. Patients are placed on lists based on what organ(s) they need. The UNOS maintains separate lists for each organ combination a patient needs, kidney only, kidney and pancreas, kidney and liver, etc. A single patient can be on more than one list. If the candidate receives a transplant, the transplant center is required to remove the patient from all the other lists as a duplicate entry.

Second, the counts are for registrations not candidates. In any year, about 5% of the kidney-only candidates (patients on the kidney-only waiting list) are registered at more than one transplant center. Most are people who have moved and are transferring their registration to a transplant center closer to their new address. But a few, most likely wealthy patients, are actually registered at multiple transplant centers in an effort to get an organ faster. The most famous example of this is Steve Jobs, who needed a liver transplant and had access to a corporate jet. But anybody who lives in a large city can benefit by getting on the list at a hospital in a more rural area, then traveling to that town and waiting for a donor after they reach the top of the list. Again, after the patient receives a transplant, all transplant centers are required to inform the UNOS that duplicate registrations for that patient should be removed from the list.

Third, there isn’t a direct correlation between the number of people on the UNOS waiting list and the number of people with ESRD (the prevalence rate). Once a patient receives a transplant, they are removed from the waiting list. However, they are not cured and so are still counted as having ESRD. Similarly, there is no direct correlation between the number of people added to the UNOS waiting list in a year and the number of people newly diagnosed with ESRD. That’s because a patient who enters the waiting list may have been diagnosed with ESRD years earlier. Also, they may enter the waiting list if the they previously received a kidney transplant and the organ fails.

Finally, there are two categories to the waiting list. Registrants are classified by the transplant center as either active and inactive. Active registrants are considered medically able to get a transplant immediately if an organ becomes available. Inactive registrants are currently unable to accept a transplant, but are considered good long-term candidates for a transplant. I will discuss this in more detail later.

The UNOS data is collected via a survey that each transplant center must complete for each registrant on their waiting list once a year to determine the registrant’s current status. As any of you who have dealt with survey data realize, cleaning survey response data from respondents (both the candidates and the administrators at the transplant center) who are not familiar with statistical analysis is one of the most difficult tasks in any research project and is a major source of nonsampling error.

Growth in prevalence of ESRD and in size of kidney transplant waiting list

In 2007, the latest year data is available, about 111,000 people in the U.S. were diagnosed with ESRD for an average incidence rate of 361 per million population. Figure 1 shows the incidence rate of ESRD has been rising dramatically over the past two decades, though it seems to have peaked. Blacks are more than three times likely to be diagnosed as whites. The ratio of prevalence by race is not as high, meaning that once diagnosed, whites tend to live longer with ESRD than blacks.


Figure 1. Incidence and prevalence rates for ESRD by race. Data from USRDS

In 2007, the prevalence of ESRD was about 1,700 per million population, representing over 527,000 people. Of these people, about 150,000 have a functioning transplanted kidney and 375,000 are on dialysis. (The remainder refuse treatment and will die within a few months.) However, as shown in Figure 2, there were only 78,300 registrants (and fewer candidates) on the UNOS transplant waiting list. This means only one-fifth of patients on dialysis were on the UNOS waiting list. As discussed in earlier blog posts (Dec 5 and Dec 18), the reasons people fail to get on the waiting list are complex.


Figure 2.Total active and inactive wait list. Data from UNOS

Figure 3 shows even though the number of transplants is growing (right), the incidence rate of ESRD is growing faster (left), so the wait times for a deceased donor kidney is getting longer (center) and the transplant rate is falling (left). For every 100 people newly diagnosed with ESRD in 2007, there were only four transplants.


Figure 3. Transplant trends. Data from USRDS

Growth in the UNOS waiting list

Figure 4 shows the number of new registrants being added to the active list each year rose from about 17,000 in 1995 to 25,000 in 2004 and has flattened out since then. Unfortunately, the number of transplants, from either deceased or live donors, has not kept pace. The seemingly good news is that the number of registrants removed from the active list without a transplant (which consists of people who decide they no longer want a transplant, are too sick for a transplant, or die) has not been growing. The categories that has been growing (and growing rapidly) are movements to and from the inactive list, with more patients going to the inactive list than coming from it. Notice the size of this churn represents a large proportion (more than one-fourth) of the active waiting list population.


Figure 4. Active wait list. Data from UNOS

Figure 5 shows the rapid growth of the inactive waiting list. First, notice the jump in the number of new inactive registrations starting in 2004. The most common reason for being initially placed on the inactive list is an incomplete evaluation by the transplant center. That is, the patient starts the evaluation process but is unable to complete it before the survey date (perhaps due to difficulty getting transportation to the transplant center). Other reasons for being on the inactive list are the presence of treatable comorbidities such as obesity, addiction (smoking, alcohol, or drugs), hypertension, or type 2 diabetes.

Next, notice the large number of registrants moving to the active list. Many of them are the new registrants who have completed their evaluations and are moved to the active waiting list, but also includes a large number of registrants who started as active and were on the inactive list for a period of time.

Most of the people on the inactive list are removed without a transplant, which makes sense, since they were not considered good transplant candidates. However, when coupled with the large flow of registrants from the active list (equal to about half of the total number of inactive registrants each year), this may also indicate that many transplant centers are moving active candidates to the inactive list rather than removing them entirely. Thus, the inactive list may contain many registrants who are too sick to receive a transplant and have little chance of recovery prior to death.

There are a large number of registrants in the Not coded category. This indicates that people on the inactive list are less likely to be in close contact with their transplant center and either could not be contacted or incorrectly completed the survey.


Figure 5. Inactive wait list, data from UNOS


In a future post, I will continue to explore the USRDS and UNOS data to revisit the issue of long wait times experienced by patients with type O blood.

[Update1: Added explanation that the counts of incidence and prevalence cannot be directly compared to the counts on the waiting list.]

[Update2: Corrected an error in proportion of patients with ESRD on the UNOS waiting list. Patients who have a functioning transplant should be excluded from the calculation.]