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INTRODUCTION
Optimized allocation of the deceased donor organs is a matter of concern for waiting list patients for liver transplantation (LT). In Korea, a nationwide allocation system for deceased donor liver grafts was started in February 2000 after the establishment of the Korean Network for Organ Sharing (KONOS) that was modeled after the United Network for Organ Sharing [1,2]. This system utilized a Child-Turcotte-Pugh (CTP) score-based allocation system, similar to what had been used in the United States before the adoption of the model for end-stage liver disease (MELD) score-based allocation system. The annual number of deceased organ donors in Korea is much lower than in many Western countries, and a serious deceased donor organ shortage has led to high waiting list mortality rates. As such, the Korean MELD score-based allocation system was adopted in June 2016 to optimize the use of the deceased donor liver organs [3-5].
To date, this new allocation system has been successfully practiced for more than 3 years. However, the number of deceased donors in Korea did not increase over this period. As a result, the majority of the deceased donor liver organs were allocated to patients with very high MELD scores [6]. This study analyzed the detailed allocation outcomes of the deceased donor liver transplantation (DDLT) for the first 2 years after implementation of the Korean MELD score-based liver allocation system at a high-volume LT center in Korea.
METHODS
Study Design
This study was a retrospective analysis using single-institution DDLT data from Asan Medical Center. The study period for patient selection included the 2 years from June 2016 to May 2018, during which a total of 174 DDLT cases were performed in patients older than 12 years. The study parameters were KONOS status, MELD score, waiting period until organ allocation, admission status at organ allocation, and ABO blood group. This study was approved by the institutional review board of Asan Medical Center.
Korean MELD Score-Based Allocation System
The Korean MELD score-based liver allocation system is based on the following original calculation formula: [9.57×loge (creatinine, mg/dL)+3.78×loge (total bilirubin, mg/dL)+11.2×loge (international normalized ratio)+6.43]. Moreover, there are five MELD score status categories as follows: status 1 (acute liver failure and early graft failure), status 2 (MELD score 38–40, equivalent to KONOS status 2A), status 3 (MELD score 31–37), status 4 (MELD score 21–30), and status 5 (MELD score ≤20). Patients with hepatocellular carcinoma within the Milan criteria receive additional 4 to 5 points if their MELD score is less than or equal to 20 [6]. The pediatric end-stage liver disease (PELD) scoring is used for patients up to 12 years of age, but not included in this study.
Status 1 can be extended to a total period of 14 days. The renewal interval periods for MELD score update are the following: 7 days for KONOS statuses 2 and 3, 3 months for status 4, and 6 months for status 5. If the MELD score is not updated within the interval period, the score automatically decreases to 6. In addition to MELD score, identical blood groups and same country regions of the donors were assigned a priority, whereas a no priority was given to donor management institution.
RESULTS
Recipient Demographics
The total of 174 recipients included 129 (74.1%) male and 45 (25.9%) female patients. The mean and median age of the recipients was 52.3±12.0 years (range, 17 to 74 years) and 53 years, respectively. The recipient age at DDLT was less than 40 years in 27 patients (15.5%), 41 to 50 years in 40 patients (23.0%), 51 to 60 years in 62 patients (35.6%), and over 60 years in 45 patients (25.9%). The primary diagnoses of these patients were summarized in Table 1, with hepatitis B virus-associated liver cirrhosis (n=54, 31.0%), alcoholic liver cirrhosis (n=53, 30.5%), cryptogenic liver cirrhosis (n=16, 9.2%), and late retransplantation (n=30, 17.2%) being the most common liver diseases diagnosed in patients at KONOS statuses 2 to 4.
The recipient ABO blood groups were group A in 65 (37.4%), group B in 51 (29.3%), group O in 28 (16.1%), and group AB in 30 (17.2%) patients. No patient carried Rh-negative blood group. The types of DDLT operation were primary LT in 141 (81.0%) and retransplantation in 33 (19.0%). The numbers of patient with in-hospital admission status at DDLT allocation were as follows: 24 (89.2%), 38 (95.0%), 60 (96.8%), and 41 (91.1%) in blood groups A, B, O, and AB, respectively.
KONOS Status Categories at DDLT
The KONOS status categories at LT allocation were status 1 in 11 patients (6.3%), status 2 in 82 patients (47.1%), status 3 in 63 patients (36.2%), and status 4 in 18 patients (10.3%) (Fig. 1). In status 1 patients, the LT types were primary LT in eight cases (72.7%) and retransplantation in three cases (27.3%) with the mean waiting period to LT of 4.7±3.8 days. The MELD score ranged from 28 to 40.
In all patients, the mean MELD scores’ distributions at initial enrollment and DDLT allocation and mean waiting period until DDLT according to the recipient ABO blood groups were the following: 30.6±7.7, 36.6±4.6, and 62.1±98.2 days in blood group A; 32.7±7.4, 37.6± 3.6, and 25.7±38.1 days in blood group B; 32.1±7.1, 38.8±2.7, and 26.0±30.5 days in blood group O; and 28.5±8.5, 34.8±5.5, and 68.4±110.5 days in blood group AB, respectively. The mean MELD scores’ comparison revealed significant statistical differences (P< 0.001). Patients with blood groups O and AB carried the highest and lowest mean MELD scores at DDLT allocation, respectively. Furthermore, the comparison of the mean waiting periods revealed significant statistical differences (P=0.012). Patients with blood group AB and blood groups B and O carried the longest and shortest mean waiting period until DDLT allocation, respectively. The KONOS status distribution according to the ABO blood groups is presented in Fig. 2, indicating that the recipients with blood group O accounted for the greatest proportion in KONOS statuses 1 and 2.
DISCUSSION
The high demand for LT in Korea is attributed to the high prevalence of hepatitis B virus-associated liver cirrhosis and subsequent high incidence of hepatocellular carcinoma [4-6]. Recently, alcoholic liver disease became one of the major LT indications in Korea [7]. The yearly number of deceased organ donors temporarily exceeded 10 per million individuals in the year 2016 [3]; however, it prospectively declined because of certain medical and social issues, including the Life Insurance Decision Act regulating termination of life-sustaining treatment. The annual numbers of deceased organ donors and those undergoing DDLT in Korea were 573 and 508, 515 and 450, and 449 and 369, in the years 2016, 2017, and 2018, respectively.
In recent years, the total annual number of LT cases in Korea remained largely unchanged, suggesting a reciprocal relationship between the case numbers of DDLT and the living donor LT [4,5,8]. Currently, critically ill patients, defined as those with very high MELD scores, are more likely to receive DDLT than before; thus, they have usually waited for significantly long time periods after enrollment in the KONOS waiting list. However, it is not possible to estimate the waiting period because DDLT allocation happens unpredictably. Thus, urgent living donor LT is also performed, particularly in critically ill patients with progressive hepatic encephalopathy [5,9].
One of the primary reasons underlying the change in the liver allocation system from the old CTP to the new MELD score-based system was that relisting was not allowed after the 2-week priority allocation in patients classified under the old KONOS status 1 or 2A. In this CTP score-based allocation system, patients who did not receive DDLT within 2 weeks could not be indicated for priority allocation again, implying that if they did not receive LT during that time, most patients, except those who received living donor LT, died [2,6]. Paradoxically, this system was implemented to restrict the pool size of critically ill patients on the waiting list. With the new MELD score-based allocation, the pool size was gradually expanded because patients were allowed to wait for prolonged periods until DDLT or death without LT. Since the number of deceased organ donors cannot meet the demand for DDLT in critically ill patients, a priority allocation was made only for patients with the highest KONOS status.
In this study, organ shortage significantly affected patients belonging to the blood group O, which was reflected to LT in this study. The LT candidates with blood group O were initially enrolled at a mean MELD score of 32.1±7.1 and allocated to DDLT at a mean MELD score of 38.8±2.7 after a mean waiting period of 26.0±30.5 days. Their MELD score at DDLT allocation was the highest, compared with other blood groups. Conversely, LT candidates with blood group AB had the lowest MELD score, compared with those with other blood groups.
Several studies have summarized the results following the introduction of MELD scoring in deceased donor liver organ allocation. Freeman et al. [10] reported that the MELD/PELD score-based system in the United States has been associated with reduced registrations and improved LT rates without increasing the mortality rates for individual groups of waiting candidates or changes in early transplant survival rates [10]. In addition, Ben-Haim et al. [11] concluded that MELD score was valid in Israel and superior to the CTP score for predicting waiting list mortality. Although longer waiting time due to organ scarcity is a key factor, death rates in the mid-range MELD groups indicate that further audit of the care of patients with end stage liver disease is indispensable [11]. Moreover, Castro et al. [12] found that patient survival on the waiting list for LT remained unchanged for 1 year after the introduction of MELD scoring in Brazil. The collective review by Chaib et al. [13] indicated that MELD scoring significantly improved short-term survival of the sickest patients on the waiting list for LT.
In addition, the results of this study indicate that the Korean MELD score-based liver allocation system was greatly influenced by a serious shortage of deceased donors [3]. The mean MELD score of DDLT recipients exceeded 36, suggesting that only patients with very high MELD scores were allocated to DDLT due to the severe organ shortage in Korea. Before the MELD score-based allocation system adoption, the new KONOS statuses 2 and 3 had been expected to cover approximately a half of the DDLT cases, with a considerable proportion of liver grafts allocated to status 4 patients carrying MELD scores between 21 and 30. However, in reality, the proportion of the statuses 2 and 3 patients was much greater than anticipated. Recent decreases in the number of deceased donors resulted in the expansion of the waiting list pool of patients with very high MELD scores. We presume that this deleterious outcome was responsible for the current rise in the MELD score cutoff enabling liver allocation. Unless the number of the deceased organ donors is significantly increased, the mean cutoff score for DDLT allocation will not be lowered.
This study has several notable limitations. First, it was a single-center study, which may potentially introduce a selection bias. Hence, nationwide follow-up studies are needed to validate our results. Second, the waiting list mortality and posttransplant outcomes were not assessed in this study.
In conclusion, the new Korean MELD score-based liver allocation system was successfully established at a high-volume LT center during the first 2 years. Serious deceased organ donor shortage resulted in very high MELD score cutoffs for DDLT allocation. Furthermore, there was a significant inequality in the possibility for DDLT according to blood group compatibility. Unless the number of the deceased organ donors significantly increases, the mean cutoff for DDLT allocation will not be lowered. Large-scale nationwide follow-up studies are needed to precisely delineate the allocation status of DDLT.
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