1. What is united network of organ sharing (UNOS)?

UNOS is the nonprofit, scientific and educational organization that administrates over the United States national organ registry known as the Organ Procurement and Transplantation Network (OPTN). UNOS originated as an initiative of The South-Eastern Organ Procurement Foundation (SEOPF) in 1977. SEOPF was the first organization to develop a computerized system that used medical information to match potential organ donors and recipients. SEOPF started the Kidney Center in 1982, which evolved into UNOS. The National Organ Transplant Act was passed in 1984 by the US Congress and established the OPTN. UNOS was appointed administrator for OPTN and continues in this role today. UNOS is involved in multiple aspects of organ transplantation and donation, including managing the wait list, matching donors and recipients, maintaining the US national organ transplant database, policy development, ensuring adherence to organ allocation policies, and providing organ transplantation education for the general public and medical professionals. The Scientific Registry of Transplant Recipients (SRTR) does an annual data collection for kidney transplants across the United States, which is available online at www.ustransplant.org .

2. What is involved in kidney allocation?

The process of allocating a kidney to a recipient is an intricate process. The procuring organization accesses the national transplant computer database, UNet ^sm , through the Internet or contacts UNOS directly. In either situation, information about the kidney donor is entered into UNet ^sm and a donor/recipient match is determined for each donated kidney.

All transplant candidates incompatible with the donor for medical factors such as blood type are eliminated from the match list. The match list of potential recipients is then ranked according to objective medical criteria (body habitus, blood type, tissue type, size of the organ, medical urgency of the recipient, time accrued on the waiting list, and distance between donor and recipient). Survival benefit was added as an additional factor in 2015 (see Question 3).

Using the match of potential recipients, the local organ procurement coordinator or an organ placement specialist contacts the transplant center of the highest-ranked patient and offers the organ to that center. If the kidney is rejected, the next potential recipient’s transplant center is contacted. Calls are made to multiple recipients’ transplant centers in succession to expedite the organ placement process until the kidney is placed. Once the kidney is accepted for a patient, transportation arrangements are made and the transplant surgery team is notified.

3. What important factors are weighed in the new kidney allocation score?

There were significant changes made to the allocation system in December of 2014.

• •
  

  Estimated Post Transplant Survival Score (EPTS): This is an estimate of patient longevity. The score is 0% to 100%, with higher scores associated with poorer survival. It is calculated using the patient’s age, dialysis time, diagnosis of diabetes, and history of prior transplant. It is not used in pediatric patients. The EPTS score is divided into large two groups, 0% to 20% and those over 20%. Previous organ transplant or long dialysis vintage increase EPTS scores. An individual with an EPTS score of 0% to 20% will be prioritized over candidates with higher scores, but only for the highest-longevity kidneys, which are those kidneys with a Kidney Donor Profile Index (KDPI) of less than or equal to 20%. Patients with an EPTS of 0% to 20% will receive priority for zero mismatches, local offers, as well as regional and national offers. The EPTS score is recalculated regularly.

  
  
• •
  

  KDPI: The KDPI quantifies the health of a donated kidney. It is calculated based on:

  
  
  
  
  • •
    

    Age

    
    
  • •
    

    Height

    
    
  • •
    

    Weight

    
    
  • •
    

    Ethnicity

    
    
  • •
    

    History of hypertension or diabetes

    
    
  • •
    

    Cause of death

    
    
  • •
    

    Terminal creatinine

    
    
  • •
    

    Hepatitis C status

    
    
  • •
    

    Whether the donated organ was after circulatory death

  
  
  
  
• •
  

  KDPI replaced the terms Standard Criteria Donor (SCD) kidney and Expanded Criteria Donor (ECD) kidney to better estimate kidney longevity. Therefore a kidney with a KDPI <20% based on the calculated factors should survive longer than 80% of the previous years’ harvested kidneys. On average, a kidney with a KDPI of <20% for the last 11.5 years, a kidney with a KDPI of 20% to 85% over the last 9 years, and a kidney with a KDPI >85% is expected to function for over 5.5 years. A patient who previously would only accept an SCD kidney would default to accepting a kidney with a KDPI of <85%. If the patient is consented to an ECD kidney, the KDPI of the kidney can be over 85%. Only individuals with an EPTS score <20% have access to a kidney with a KDPI <20%. This is for longevity matching so patients with longer expected survival time receive kidneys with the longest expected survival time.

  
  
• •
  

  Time on the Wait List: Patient with longer wait time has priority. Another change to the allocation system made in 2014 was to credit time on dialysis prior to listing. So a patient who has been on dialysis for 2 years prior to getting on the transplant list will start with 2 years of wait time.

  
  
• •
  

  Age: In the new allocation policy, pediatric patients will receive priority over adult patients for donors with a KDPI score <35%, regardless of donor age. This is a change from the previous policy where the organ priority for pediatric patients was based on age of the donor (<35 years of age) as opposed to the KDPI score. Age is a factor in calculating KDPI and EPTS.

  
  
• •
  

  Medical urgency: Only considered in local kidney allocation

  
  
• •
  

  Human leukocyte antigen mismatch: Priority to zero antigen mismatch

  
  
• •
  

  Degree of panel reactivity antibody (PRA): In the old system, patients with a calculated PRA (cPRA) >80% received 4 points and those below this cutoff received 0 points. The more of these points a patient accumulates, the more priority they receive for transplant. This puts the patient who has some degree of sensitization at a disadvantage. In other words, though it is more difficult to find an organ for a patient with a cPRA of 70% versus one with a cPRA of 20%, in the old system they were treated the same. In the new allocation system, to help rectify this, the points are assigned when the cPRA is ≥20% according to a sliding scale. The greater the cPRA, the more points awarded, so those with the highest cPRA >98% receive the most points. However, patients with a smaller degree of sensitization do also receive some benefit as compared to before.

  
  
• •
  

  Blood type: Patients with blood type B have longer wait times generally than the other blood types. Blood type B is more common in blacks. In the old allocation system, a patient with blood type B could only receive a kidney from a donor that was blood type O or B. In the new allocation system, they can receive an organ from a donor with blood types O, B, A2, or A2B. The patient must have a low anti-A IgG titer prior to transplant if they are to be a candidate for an A2 or A2B kidney (also see Question 8, Chapter 56 ).