Staged preoperative evaluation of potential living donors for liver transplantation

Introduction

Background

Low organ donation rate is a limiting factor in liver transplantation. The growing disproportion between the number of candidates listed for liver transplant and the availability of deceased organ donors is a problem in almost all countries, and the mortality on liver transplant waiting lists globally ranges from 5–25% (1,2). In this scenario, living donor liver transplantation (LDLT) has been developed to increase organ availability, achieving excellent donor and recipient outcomes. Currently, there are data from over 15,000 LDLT worldwide, demonstrating similar results to those obtained with deceased-donor graft (3-5).

The LDLT technique has several advantages for the recipient: transplant can be performed electively before serious decompensation occurs in the recipient, complications associated with organ preservation are minimized, optimal quality of grafts are provided and it offers the possibility of liver replacement to selected patients who may be ineligible for deceased donor organ transplant (6). The main concerns with this type of liver donation are the potential risk of death or serious complications in the donor and the technical complications in the recipient. For this reason, selection of a suitable donor is crucial to minimize postoperative donor complications and to improve graft and patient survival for the recipient. The aim of donor evaluation is to determine whether or not the donor is medically and psychologically suitable for living donation (7-9).

During the evaluation of potential donors, only some of them will be eligible for living liver donation, due to ABO compatibility, liver anatomy and potential donor comorbidities. Additionally, during and/or after the donor evaluation process, the recipient may not become suitable for live donor liver transplantation due to disease progression, earlier availability of a deceased donor and liver transplantation, or waitlist mortality. As a result, only a small fraction of potential donors are able to ultimately undergo donor hepatectomy.

Rationale and knowledge gap

There are few studies in the literature evaluating the main reasons for discarding potential donors. In Latin America, as in many low and middle income health care systems, it is essential to understand the main reasons for donor unsuitability in order to make a more efficient use of time and resources in LDLT.

Objective

We conducted this study to describe the selection process and the outcomes of the preoperative evaluation of living donors, identifying the main reasons for discarding potential donors, and evaluating the main anatomical findings in liver donors evaluated in our program. We present this article in accordance with the STROBE reporting checklist (available at https://tgh.amegroups.com/article/view/10.21037/tgh-24-65/rc).

Methods

We conducted a retrospective study with data from our center at Pontificia Universidad Católica de Chile. All potential donors evaluated in our adult-to-adult LDLT program between April 2018 and July 2021, were included. We focused on the adult liver transplant program and excluded donor evaluations for pediatric transplantation.

Selection process in our center

In our center, a step-by-step evaluation is performed to determine which potential donor should be excluded from the donation process. Below we describe the 3-stage selection process (Figure 1).

Figure 1 Initial flow chart of potential donor selection. This flowchart details the multi-stage process involved in selecting potential liver donors, beginning with demographic screening and progressing through clinical evaluations, psychological assessments, laboratory tests, and radiological evaluations. The figure is designed to provide a clear and comprehensive view of the rigorous selection process undertaken by the transplant team to ensure the safety and suitability of living donors. CMV, cytomegalovirus; HIV, human immunodeficiency virus; HSV, herpes simplex virus; EBV, epstein-barr virus; BMI, body mass index; MRCP, magnetic resonance cholangiopancreatography; GBWR, graft to body weight ratio.

Our recipient selection criteria for living donor liver transplantation included all recipients that were considered for deceased donor liver transplantation, from 18–75 years old, for all Model for End-Stage Liver Disease (MELD) scores and including patients under a transplant oncology protocol beyond deceased donor listing criteria. Recipients for retransplantation and/or complex vascular anatomy evaluated by the surgical team, were not considered for living donor transplantation.

First stage

This stage is performed by our transplant nurse who makes a demographic screening to the potential donors. Donor must have a compatible blood type with the recipient, be younger than 60 years and older than 18 years and a consanguineous relative of the recipient up to the 4^th degree or his/her spouse or partner. Living unrelated donors are considered if these are in-law related up to the 2^nd degree since January 2021. All living donor candidates underwent a first clinical visit with a transplant surgeon and the living donor coordinator. This initial visit must guarantee the psychological adequacy of the donor and ensure the voluntary nature of the act of donation and that they truly understood the risk of the procedure. Likewise, the competence and autonomy of the donor between 18 and 25 years, must be evaluated. In this stage we included education on the availability of a deceased donor, progression or mortality of recipient on waiting list and existence of a better candidate for living donor as causes for discarding a donor candidate.

Second stage

Once the potential donor has passed the first stage and if he/she is eligible for donation, a complete clinical evaluation is carried out, with laboratory and serological tests. All potential donors must undergo a medical evaluation by a hepatologist, a psychiatrist and an independent physician outside the transplant team. A complete blood cell count, blood biochemistry values, coagulation tests and viral serological panel [hepatitis A, B, C, cytomegalovirus (CMV), human immunodeficiency virus (HIV), Herpes Simplex Virus (HSV), Esptein-Barr virus (EBV)]. In patients with suspected heart disease, an echocardiogram is performed and if necessary, a stress echocardiogram. Exclusion criteria for living liver donors include history of deep vein thrombosis, use of contraceptives (waiting period of 2 months), alcohol or drug abuse, body mass index (BMI) greater than 30 kg/m², among other medical and/or psychological concerns.

Third stage

In the third stage, we performed a contrast enhanced triple-phase abdomen and pelvis computed tomography (CT) (Philips Brilliance with 64 channels; Philips Healthcare, Amsterdam, The Netherlands or General Electric Birghtspeed with 16 channels; General Electric Healthcare, Chicago, IL, USA), and a magnetic resonance cholangiopancreatography (MRCP) on all potential living donors (Siemens Magnetom Avanto; Siemens Medical Solutions, Erlangen, Germany), in order to assess the liver bilio-vascular anatomy and to perform a liver volumetric analysis of the potential liver graft. For the volumetric analysis, we used the software Intellispace portal V9 from Philips®. From the volumetric analysis, graft-to-recipient weight ratio (GRWR) is calculated, and the potential donors with a result lower than 0.8% are excluded from the donation in order to avoid the risk of small-for-size syndrome in the recipient. MRCP is also performed in all potential donors that reach this stage, to assess the biliary anatomy and the degree of steatosis in the potential liver graft. Potential donors with hepatic fat fraction less than 8% on magnetic resonance imaging (MRI) are deemed acceptable. When fat fraction is over 8%, a liver biopsy is required to demonstrate hepatic steatosis of less than 10%. Patients with 10–20% hepatic steatosis and/or BMI over 30 kg/m² are evaluated for potential weight loss and reassessment with MRI and biopsy. Thus, we minimize the need for a liver biopsy, only for patients with persistently high % fat fraction after weight loss, or donors that do not have the time to lose weight given recipient’s severity, and the biopsy will clarify the exact level of steatosis.

Anatomical unsuitability is decided by the liver transplant surgeon team in a case-by-case discussion in our living donor multidisciplinary meeting. The development of a living donor program requires clinical judgement and initial strict selection of donors, that may be modified over time with more team experience and expertise. Absolute contraindications included a potential graft with 3 hepatic ducts or 2 hepatic arteries. The presence of 2 portal veins was considered unsuitable during the initial years, but has been accepted lately with reconstruction of both portal vein branches in the backtable. Accumulation of anatomical variations was also considered in this evaluation.

Statistical analysis

Medical records were reviewed, registering: sociodemographic data (age, gender, BMI and ABO blood group), radiological data (liver volumetry, anatomical variation of hepatic artery, bile duct, portal vein, focal liver lesions and extrahepatic malignant tumors, steatosis), and the reason for discard.

The data obtained was collected in a database in Microsoft Excel software. Qualitative variables are presented using absolute number and percentage. Numerical variables are presented using mean and standard deviation (SD).

Ethics

The study was conducted in accordance with the Declaration of Helsinki (as revised in 2013). The study was approved by the Health Sciences Scientific Ethics Committee of Pontificia Universidad Católica de Chile (No. 240920001). Informed consent from participants was not required for this study due to the retrospective nature of the research.

Results

Demographic and clinical data

From April 2018 to July 2021, a total of 231 potential living liver donors underwent an evaluation in our center. The demographic and clinical data are summarized in Table 1. The mean age of patients was 37.2 years old (±11.1 years). One hundred and twenty (51.9%) patients were male. The mean BMI of the potential donors was 26.8 kg/m² (±3.5 kg/m²). Most of them were son/daughter or siblings of the recipient [114 (49.4%) and 41 (17.7%), respectively]. The most frequent ABO blood group was O [n=166 (71.9%)], followed by group A [n=56; (24.2%)]. Most patients were Rh blood group positive [n=224; (96.9%)].

Causes for discarding

The causes for discarding potential donors are summarized in Tables 2,3. Of the 231 donor candidates, 101 (43.7%) were discarded in the first stage and didn’t complete the radiological evaluation. The main causes were the availability of a deceased donor [n=32/101; (31.7%)], drop-out due to disease progression or waitlist mortality of the recipient [n=20/101; (19.8%)], ABO incompatibility [n=14/101; (13.9%)] and the existence of a better candidate for living donation [n=10/101; (9.9%)]. In the third stage, 123 CT and 102 MRCP were performed. Of the 130 potential donors who underwent a CT and/or MRCP, the main causes of anatomical unsuitability were small liver remnant (SLR) [n=25/130; (19.2%)], steatosis [n=17/130; (13.1%)] and biliovascular unsuitability [n=11/130; (8.5%)]. Of all patients with steatosis on MRCP, only 2 donors required a biopsy after weight loss (no steatosis and 10% steatosis without fibrosis or periportal inflammation, respectively), and both underwent successful liver donation.

Of all 231 potential donors evaluated, 75 were accepted as suitable anatomical donors (32.5%), 71 were accepted after multidisciplinary evaluation (30.7%), and 36 candidates underwent liver donation (15.6%). The flow chart of the donor evaluation is synthetized in Figure 2.

Figure 2 Flow chart of potential donor evaluation.

Radiological evaluation

The findings in the radiological evaluation in the potential donors are summarized in Tables 4-9. Of the 130 patients who completed their radiological evaluation, 51 donor candidates had anatomic variation of the hepatic artery [n=51/130; (39.2%)]. The most frequent variations were: a replaced right hepatic artery (RHA) from superior mesenteric artery (SMA) or accessory RHA (type III or VI in Michels classification) [n=18/51; (35.3%)], a replaced left hepatic artery (LHA) from left gastric artery (LGA) or accessory LHA (type II or V in Michels classification) [n=11/51; (21.6%)] and a completely replaced common hepatic artery (CHA) from SMA (type IX in Michels classification) [n=7/51; (13.7%)].

Twenty-nine donors had anatomical variation of the bile ducts [n=29/102 who had MRCP; (28.9%)]. The most frequent variations were: drainage of the right posterior hepatic duct into common hepatic duct [n=16/29; (55.2%)], drainage of the right posterior hepatic duct into the left hepatic duct [n=8/29; (27.6%)].

Twenty-six donor candidates had anatomic variation of the portal vein [n=26/130; (20%)]. The most frequent variation was to have two independent right portal veins, as an extraparenchymal branching of the right anterior portal vein from the left portal vein (type C in Nakamura classification) [n=10/26; (38.5%)], followed by trifurcation of the portal vein (type B in Nakamura classification) [n=5/26; (19.2%)], intraparenchymal branching of the right anterior portal vein from the left portal vein (type D in Nakamura classification) [n=4/26; (15.4%)] and undivided main portal trunk (type E in Nakamura classification) [n=4/26; (15.4%)].

Eleven potential donors had focal liver lesions [n=11/130; (8.5%)], being hemangioma [n=5/11; (45.5%)] and focal nodular hyperplasia [n=3/11; (27.3%)] the most frequent. Extrahepatic malignant tumors were identified in 2 patients, and the final diagnosis were intestinal gastrointestinal stromal tumor (GIST) and a renal cell carcinoma. Of the 130 patients who completed their radiological evaluation, 116 performed a liver volumetry. The mean standard liver volume was 1,446.36 mL (±303.59 mL). The mean right and left liver volume were 966.3 mL (±220.7 mL) and 467.3 mL (±105.4 mL), respectively. The mean future liver remnant was 34.3% (±9.8%) and the mean GRWR was 1.4% (0.5%).

Out of the 130 patients that completed the third stage and had complete radiological evaluation, 55 (42.3%) were discarded due to radiological findings including small liver remnant (n=25, 45.5%), liver steatosis (n=17, 30.9%), vascular anomaly (n=11, 20%) and extrahepatic malignant tumor (n=2, 3.6%) (Table 3). Only 75 patients were considered adequate donors radiologically and 36 of them underwent donation.

CT performance

Of the 123 potential donors who underwent a CT, 75 were adequate anatomical donors (60.9%). A total of 96% of donors with adequate anatomy on CT were deemed adequate donor candidates after evaluation.

Discussion

Living donor selection is essential to minimize postoperative donor complications and to improve recipient outcomes, and knowing the main reasons for discarding donor candidates is important in order to make more efficient the use of time and resources in a LDLT program. In the observational study conducted by Dirican et al. in 2015, they found that 31% of the potential donors were accepted as suitable for donation (9). In a similar way, Karakaya et al. in 2020, reported 32.3% of donor candidates as suitable for donation over 1,387 patients (10). This is similar compared with the 32.4% of potential donors, accepted as adequate donors in our study. In the study performed by Dirican et al., 29% of the potential donors underwent donation, meanwhile in our study, we found that just 15.6% finally underwent liver donation. The cause of this could be that only 2% of their potential donors were discarded due the availability of a deceased donor and 0.9% due progression or mortality of the recipient in the waiting list, meanwhile in our study we found that 13.9% (n=32/231) and 8.7% (n=20/231) were discarded for these reasons, respectively. In their study, the main causes for unsuitability for liver donation were small liver remnant in 43% and steatosis in 38.4%. This is similar compared with our findings (45.5% and 30.9%, respectively) (9).

The BMI is an important factor in the selection of an appropriate living donor, the degree of hepatic steatosis is a major concern. In living liver donors with hepatic steatosis, macrovesicular fat level ≥30% are thought to increase the risk of poor graft function or decreased graft survival. Higher fat levels also affect donor safety. Therefore, assessment of BMI in the first step of potential liver donor evaluation should be emphasized. In our series the mean BMI of the potential donors was 26.8 kg/m² (±3.5 kg/m²) (11,12).

The CT provides valuable information that will be useful in choosing the most suitable candidate and in identifying anatomic variants that may alter the surgical approach or exclude the potential donor. The anatomic variants of the hepatic artery are common and present in approximately 42% to 55% of cases, and the most frequent are: a replaced or accessory RHA arising from the SMA (type III and VI) and a replaced or accessory LHA arising from the LGA (type II and V) with 33% and 35% of the cases with anatomical variant, respectively (13-15). In a recent study conducted by Imam et al. in 2021, they analyzed the anatomic variant of the hepatic artery of 210 potential donors and found variants in 30% of the potential donors being type III or VI and type II or V the most frequent, representing the 30% and the 52.8% of the cases with anatomical variant, respectively (16). In a similar study conducted in 2020 with 610 potential donors, Yan et al. determined that type III or VI and type II or V represents only 13% and 32% of the patients with anatomical variants of the hepatic artery (17). In our study, we found type III or VI were the most frequent variant of the hepatic artery (35.3%) followed by type II or V (21.6%).

The anatomical variations of the portal vein appear in approximately 10% of cases. Covey et al. in 2004 retrospectively reviewed 216 CT in a single institution and they found a 35% variation of the portal vein (18). In a large series of 1,384 patients reviewed by Koc et al. in 2007, the portal vein variation was reported to be 21.5% (19). In 2021 Katsourakis et al. conducted a systematic review with 3,715 patients included. In their analysis, the percentage of portal vein variation was 25%. In our series, 20% of the donor candidates had anatomical variation of the portal vein, which is similar to those reported in the literature (20). In the Nakamura classification, trifurcation of the portal vein (type B) and extraparenchymal branching of the anterior branch from the left portal vein (type C) presents in approximately 2.5% of the cases, each. The intraparenchymal branching of the anterior branch from the left portal vein (type D) presents in approximately 1.7% of the cases. An undivided main portal trunk represents 0.8% of the cases (21). In the study of Katsourakis et al., trifurcation of the portal vein (type B) represents 46% of the anatomic variation of the portal vein and the branching of the anterior branch from the left portal vein (type C and D) represents 39.5% of the anatomic variations. In our study, the most frequent finding was an extraparenchymal branching of the anterior branch from the left portal vein (type C) (38.5%), followed by trifurcation of the portal vein (type B) (19.2%) and intraparenchymal branching of the anterior branch from left portal vein (type D) (15.4%) (20).

Anatomical variations of bile ducts are common and important to highlight before LDLT. Anomalous biliary tract anatomy is present in 40% of the population and unanticipated biliary variations may be a source of post-transplant complications such as biliary leakage, strictures, and graft failure. Prior knowledge and timely planning improve the outcomes (14,22). The variation includes: trifurcation (20.8% to 49% of the anatomic variation of the bile duct), the right posterior duct draining into the left hepatic duct (14% to 61.7% of the anatomic variation of the bile duct), the right posterior duct draining into the common hepatic duct (1.4% to 20.3% of the anatomic variation of the bile duct); and the right posterior duct draining into the cystic duct (1.8% to 3.3% of the anatomic variation of the bile duct) (23-27). In our study, we found 22.3% of the donor candidates had anatomic variation of the bile ducts and the most frequent were: drainage of the right posterior hepatic duct into common hepatic duct (55.2%), drainage of the right posterior hepatic duct into left hepatic duct (27.6%).

During the evaluation of potential donors, unexpected findings can be reached, and these could be in some cases very relevant for the patient. The finding of an unexpected malignant tumor in the preoperative evaluation of a potential living donor is a rare scenario, but in a high-volume transplant center, it will happen. In our study, we found 2 extrahepatic malignant tumors in the evaluation of donor candidates, 1 renal cell carcinoma and 1 intestinal GIST. In the observational study conducted by Karakaya et al. in 2020, they found 6 extrahepatic malignant tumors over 1,387 donor candidates (2 pancreas adenocarcinoma, 1 ovarian carcinoma, 1 renal cell carcinoma, 1 thyroid papillary carcinoma and 1 osteosarcoma) (10).

An increasing body of literature of living donors demonstrated the potential financial impact on the donor’s social relationships due to the donor using personal/family savings or retirement funds. Since donor evaluation is an expensive process that must be afforded by the patient and their family, in our center we are looking for a more efficient, less expensive and equally safe formula this evaluation (28-31). In our series, we found that 60.9% of the potential donors that underwent a CT were finally considered as accepted donors on multidisciplinary evaluation. We consider that a CT-first approach in the potential living donor evaluation could be a more efficient selection process, because it would identify anatomical factors that precludes the transplantation in a first stage of the evaluation and the patient shouldn’t spend more resources in complete a futile process. After this study we have modified our algorithm and flow chart of the selection process, to include the CT in the first stage of our evaluations (Figure 3). This avoids the high costs of laboratory tests and subspecialty evaluation on the 39.1% of patients that are not anatomically suitable for donation.

Figure 3 Modified flow chart of potential donor selection: “CT-First Approach”. CT, computed tomography; GBWR, graft to body weight ratio; CMV, cytomegalovirus; HIV, human immunodeficiency virus; HSV, herpes simplex virus; EBV, epstein-barr virus; BMI, body mass index; MRCP, magnetic resonance cholangiopancreatography.

Conclusions

Almost half of the potential donors didn’t complete the evaluation because of progression, death or deceased donor transplantation of the recipient. Steatosis, SRLS and anatomical variation are the main causes of dropout. Only 1/3 of potential donors are suitable for donation and half of them will undergo surgery. It is important to know the main exclusion criteria met by potential donors, in order to make a more efficient use of time and financial resources. CT-first approach decreases the high cost of laboratory tests and evaluations on 40% of patients who are not anatomically suitable for living liver donation. Out of all anatomically suitable donors on CT-scan, 96% of them will be approved after complete donor evaluation. Considering that, the CT-first approach seems to be a more efficient selection process, and we strongly suggest further research to validate this approach.

Although the rate of discarding living donors is quite high, the implementation of this program, the only LDLT program in our setting, has successfully positioned itself as a viable alternative to increase the availability of liver grafts, offering this alternative to every recipient in the country, covering their costs with the public health insurance.

The low rate of potential living liver donors who ultimately donated seems to be due to both strict guidelines and the simultaneous presence of a robust cadaveric program. Emphasizing that the availability of a deceased donor was 32/231 (13.9%).

It is also important to highlight that, since it is an initial program, our selection criteria were stricter at the beginning. However, as we gained more expertise, these criteria were progressively broadened, allowing the acceptance of more donors.

Acknowledgments

Part of the manuscript was presented at the 15th World Congress of the International Hepato-Pancreato-Biliary Association, held from 30 March to 2 April 2022, in New York, USA. The abstract can be found at https://www.hpbonline.org/article/S1365-182X(22)01424-1/fulltext.

Funding: None.

Footnote

Reporting Checklist: The authors have completed the STROBE reporting checklist. Available at https://tgh.amegroups.com/article/view/10.21037/tgh-24-65/rc

Data Sharing Statement: Available at https://tgh.amegroups.com/article/view/10.21037/tgh-24-65/dss

Peer Review File: Available at https://tgh.amegroups.com/article/view/10.21037/tgh-24-65/prf

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://tgh.amegroups.com/article/view/10.21037/tgh-24-65/coif). The authors have no conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. The study was conducted in accordance with the Declaration of Helsinki (as revised in 2013). The study was approved by the Health Sciences Scientific Ethics Committee of Pontificia Universidad Católica de Chile (No. 240920001). Informed consent from participants was not required for this study due to the retrospective nature of the research.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

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