Donor Evaluation Protocol for Live and Deceased Donors

Abstract

Donor evaluation is a critical step before proceeding with liver transplantation (LT) in both deceased donor LT (DDLT) and living donor LT (LDLT). A good, healthy graft is necessary for the success of the transplantation. Other issues in selecting a donor include the transmission of infections and malignancies from the donor. Because of the scarcity of cadaver organs, an increasing number of extended-criteria donors, or ‘marginal donors’, are being utilized. LDLT also has potential risks to the donor, and donor safety needs to be kept in mind before proceeding with LT. The current review highlights the factors to be considered during donor evaluation for living and deceased donors before LT.

While liver transplantation (LT) is an established life-saving modality for a variety of patients with liver disease, it is often limited by the availability of donor organs. Liver donor organs can be broadly classified into deceased donor [donor after brain death (DBD) and donor after circulatory Death (DCD)] and living donor. Most cadaveric organs come from DBD. For a donation, brainstem death must be confirmed by a fixed of criteria set for brain death that confirm the complete, irreversible loss of brainstem function, a non-responsive coma, the absence of spontaneous ventilation, and the absence of brainstem reflexes.¹ To overcome the scarcity of cadaveric organs, DCD, in which cardio-respiratory criteria confirm death, has been accepted by many countries. DCD can be controlled where there is a planned withdrawal of life support or uncontrolled where cardiac arrest is unexpected in a patient who cannot or should not be resuscitated.² Very few livers are harvested from uncontrolled DCD.

Deceased donor LT (DDLT) is technically less challenging and has the advantage of the availability of a larger graft size. Living donor LT (LDLT) has many advantages over deceased donor LT (DDLT). Not only does it increase the number of organs available, but elective LT can also be done, which can be timed for the patient's benefit and decrease mortality in patients on the waiting list. In acute liver failure (ALF), time is of the essence. A delay in the availability of organs can result in mortality on the DDLT list, which the availability of a living donor can overcome. The organ in LDLT is subjected to minimal preservation injury, thereby ensuring optimal graft quality. However, LDLT is technically more challenging. LDLT also has potential risks for the donor, with a 0.3–1% mortality risk, and may be associated with ethical issues.^{3, 4, 5, 6, 7}

While the number of patients waiting for LT has significantly increased in the last two decades, organ availability has not increased in parallel, resulting in increased waitlist mortality. This organ scarcity resulting from the imbalance between available organs and candidates waiting for LT has, in turn, led transplant centers to relax the criteria for organ donation to include extended-criteria donors, or 'marginal donors'.⁸ While in Western countries, most transplants carried out are DDLT, in most Asian countries, LDLT rates are higher, with more than 90% of transplants being LDLT. This is attributed to a lack of awareness among the general public and religious beliefs. However, China is an exception among the Asian countries, whereas, per current trends, more than 90% of liver transplants are DDLT. In India, LDLT is more common, and around 85% of transplants being performed currently are LDLT. There is a higher prevalence of deceased donor liver transplantation in South India as compared to North India. The current review highlights the factors to consider while evaluating living and DDbefore LT.

Deceased Donor Evaluation

It is vital to ensure appropriate management of the potential deceased organ donor, from the identification of imminent neurological death to the actual declaration of death by neurological criteria and obtaining consent for organ donation.

Declaration of Brain Death

Medically, brainstem death is the total and irreversible cessation of all brainstem functions. Various countries have their own rules and legislation regarding the declaration of brain death. In India, the Transplantation of Human Organs and Tissue Rules were framed in 2014 for brain death certification and organ donation. A team of four medical experts (a medical administrator of the hospital, an authorized specialist, a neurophysician/neurosurgeon, and a medical officer treating the patient) is required to diagnose brain death. If a neurophysician/neurosurgeon is unavailable, an anesthetist or an intensivist can be a board member in his place (subject to the condition that they are not a member of the transplant team). Testing for brainstem death is done twice, and only after both of these tests confirm brainstem death does the prospective donor become eligible for organ donation.

Management of Deceased Donor

Donor ICU management is essential to preserving organs during donor evaluation for successful recovery of donor organs. Maintaining donor homeostasis until graft retrieval is of utmost importance and has a bearing on successful outcomes after transplantation. Fluid management should be done using hemodynamic monitoring to maintain optimal mean arterial pressure (MAP) and urine output with a low vasopressor dose. The recommended fluid for resuscitation is crystalloids or colloids, though hydroxyethyl starch should be avoided. Prolonged hypernatremia (Na >155 mmol/L) due to diabetes insipidus is associated with postoperative graft dysfunction after liver transplantation. In cases of significant hypernatremia with hypotension, vasopressin should be started at 0.01–0.04 IU/min. In patients with hypernatremia without hypotension, desmopressin can be used. The other aspects of managing a prospective organ donor include high-dose corticosteroids, thyroxin replacement (for maintaining temperature and cardiovascular instability), management of hypoglycemia, and appropriate antibiotic therapy.⁹ To optimize recovery after transplantation, donor homeostasis should be achieved with a target MAP >60 mmHg, urine output >1 mL/kg/h, temperature >35 °C, serum sodium <150 mEq/dL, normal arterial blood lactate, PaO2 >80 mm Hg, and hemoglobin> 7 gm/dL.¹⁰ Aggressive donor management in the intensive care unit is associated with more organs transplanted per donor.¹¹

It is essential to exclude contraindications for donations, such as malignancy and septicemia. A thorough history and investigation are carried out to exclude any significant disease that can be transmitted to the recipient from the donor and to assess possible risk factors impacting liver quality. A donor should ideally be an adult with an age less than 60 and free from any transmissible disease. The essential investigations that are done include ABO blood type, complete blood count (CBC), liver function test (LFT), prothrombin time (PT), activated partial thromboplastin time (aPTT), hepatitis B surface antigen (HBsAg), anti-hepatitis B core antigen (HBc), anti-hepatitis C virus (HCV), anti-HIV, and anti-cytomegalovirus (CMV). A blood and urine culture should be obtained if the donor has been hospitalized for more than 72 h. After screening for transmittable infections, a deceased brain-dead donor can be taken up for organ retrieval. A sample check list for deceased donor liver transplantation is depicted in Table 1. At the time of retrieval of the graft, a visual inspection of the potential liver graft is carried out by the team of surgeons, and if necessary, a liver biopsy is obtained. Pre-transplant liver biopsies not only help to determine the degree of steatosis but also to identify marked steatohepatitis severe fibrosis, which may be a contraindication for transplantation.

Table 1.

Check List for Deceased Donor Liver Transplantation.

Consent	Co-ordination team approaches the family
	Informed consent taken from family
	Declaration of brain death
Investigations of donor	ABO Blood group
	Hematological: Complete blood count, prothrombin time, activated partial thromboplastin time
	Biochemical: Liver function tests, kidney function tests, serum electrolytes, blood sugar, thyroid functions
	Viral markers: hepatitis B surface antigen, anti-hepatitis B core antigen, anti-hepatitis C virus, anti-HIV, and anti-cytomegalovirus
	Imaging: X-Ray chest PA view, Ultrasound abdomen
	Cultures: Blood, urine
Ante-mortem hemodynamic stability of donor prior to organ retrieval	Temperature
	Urine output/hour
	BP (Vasopressor doses)
	Serum sodium
	Arterial blood gas: pH…………pO2…………Lactate…………
Documentation	Brain death certification (Form 10 of THOTR 2014)
	Hospital death certificate
	Family consent for organ donation (Form 8 of THOTR 2014) clearly mentioning the organs to be retrieved
	In medico-legal cases: clearance from police and the post-mortem authorities

HIV, Human immunodeficiency virus; THOTR, transplantation of human organs and tissue rules.

Donation After Circulatory Death

Although there is an increasing need to use brain-dead donors with beating hearts for organ donation, there is also room for an additional source of donors, which has led to the increasing use of non-heart-beating donors for organ donation. These organ donations were initially called "donation after cardiac death.” However, these donors may be eligible for "heart donation” too; thus, the term has been replaced by "donation after circulatory death (DCD)" or organ donation following circulatory determination of death (DCDD). These organ donations are classified as per Maastricht donor categories.¹² They are classified as uncontrolled or controlled. In uncontrolled DCD, cardiac arrest is unexpected; therefore, organ retrieval time is longer. In contrast, in controlled DCD, elective withdrawal of ventilation in a potential organ donor in end-of-life situations leads to cardiac arrest, thus limiting ischemia time as preparedness for organ retrieval can be arranged during the antemortem period in such cases.

The bane of DCD is warm ischemia time (i.e., the time from the stoppage of the heartbeat to the initiation of the organ preservation procedure). Therefore, DCD grafts have a higher risk of primary nonfunction, delayed graft function, and biliary stricture. These donors can undergo rapid femoral/iliac artery cannulation for extracorporeal perfusion (using an ECMO machine) to limit ischemia time. Also, newer techniques like ex-vivo machine perfusion can further limit ischemia time and avoid the need for static cold storage.¹³

Currently, outcomes in terms of graft survival in both DBD and DCD are similar, albeit with higher rates of ischemic cholangiopathy in the DCD group.^{14, 15, 16} However, with careful selection of donors (avoiding elderly or obese donors and limiting ischemia time), favorable outcomes can be achieved. Also, with the use of in-vivo and ex-vivo perfusion techniques, ischemic biliary complications can be reduced further.¹⁷

In India, although a few DCDs have been carried out, they are not as common. While there are published series of DCD kidney transplants, only a few unpublished DCD liver transplants have been done. The biggest hurdle to DCD in India has been a lack of clarity in the law regarding end-of-life care and withdrawal of life-sustaining treatment. Besides, there is no mention of DCD in the Transplantation of Human Organs and Tissue Rules, 1994. While DCD is feasible in India and will expand the donor pool, there is a need to increase its awareness, and protocols have to be established.¹⁸

Donor Factors Affecting Outcomes

Multiple factors related to the donor are known to influence transplant outcomes. Table 2 shows factors that need to be considered for marginal donors. These factors must be considered while choosing a donor, as they may be associated with worse outcomes like primary nonfunction and/or poor graft survival and a higher risk of biliary complications. With the increasing gap between patients requiring transplantation and the availability of organs, marginal donor organs are increasingly being utilized. The donor evaluation protocol for deceased donor liver transplantation is depicted in Table 3. Some factors that need to be considered in increasing the donor pool are shown below.

Table 2.

Extended Criteria Donors.

Risk of poor graft function	Risk of disease transmission
Older donors (>60 years)	IgG anti HBc antibodies
Obesity	Anti-HCV antibodies
Steatosis graft (>30%)	Active infection
Partial/split graft	Known donor malignancy
Donation after cardiac death
High doses of inotropes
Hypernatremia (serum Na >155 mEq/L)
Prolonged cold ischemia >12 h

HBc, hepatitis B core; HCV, hepatitis C virus.

Table 3.

Donor Evaluation Protocol in Deceased Donor Liver Transplantation.

•Identification of prospective organ donors: Identification of the cause of coma and exclusion of malignancies and active sepsis

•Basic investigations: Blood counts and metabolic parameters, cultures, blood grouping, viral serologies (HBsAg, nti HCV, Total Anti HBc, HIV, CMV serology), ultrasound abdomen

• Donor maintenance: ○ Appropriate antibiotic therapy ○ Inotropes/fluids to aim for target MAP >60 mmHg ○ Urine output >1 mL/kg/h ○ Temperature >35 °C ○ Correct hypernatremia to aim for serum sodium <150 mEq/dL: • In cases of hypotension, vasopressin should be started at a dose of 0.01–0.04 IU/min. • In cases of significant hypernatremia without hypotension, desmopressin can be used. ○ Normal arterial blood lactate ○ PaO2 >80 mm Hg ○ Hemoglobin >7 gm/dL ○ Correction of hypoglycemia ○ High-dose corticosteroids ○ Thyroxin replacement

• Confirmatory tests for brainstem death & consent

CMV, cytomegalovirus; HBc, hepatitis B core; HBsAg, hepatitis B surface antigen; HCV, hepatitis C virus; HIV, human immunodeficiency virus.

Age of Donor

Most studies have shown that donor ages beyond 55–60 years are associated with lower graft survival.^{19, 20, 21} Although changes related to liver aging are not reflected in routine lab testing, advancing age reduces cytochrome P450 content and reduces bile and hepatic blood flow.²² The hepatocyte volume, number, and regenerative capacity are also adversely impacted.²³ These changes can potentially adversely affect liver graft function by decreasing its regenerative capacity; hence, older liver allografts have a lower tolerance for preservation. Donor age has been shown to correlate with primary dysfunction and early mortality.^{21,24, 25, 26} Elderly donors have a higher prevalence of comorbidities such as diabetes and hypertension and a higher incidence of fatty liver. However, multiple reports have shown that an acceptable outcome can be obtained with older donors by limiting cold ischemia time (CIT) and choosing a graft that appears to be of good quality at harvest.^{27, 28, 29} There is no absolute limit on donor age. Allografts from octogenarian donors can achieve good outcomes if there are no other negative factors like steatosis or prolonged CIT.^{30, 31, 32} Thus, to increase the donor pool, it is essential to use grafts from elderly donors through careful selection of the donor as well as the recipient and minimizing cold ischemia time to less than 8 h.

Donor Hypernatremia

Hypernatremia has been correlated with poor outcomes, with higher rates of graft loss and poor initial graft function.^{33, 34, 35} Hypernatremia in donors may be due to derangements in fluid and electrolyte balance and diabetes insipidus in the prospective donor. The hypertonia results in increased intracellular osmolality, which may cause impaired allograft function.³⁶ Hypernatremia should be corrected before organ harvesting, and donor serum sodium >155 mEq/dL is generally considered the threshold for decreased graft survival.

Hepatic Steatosis

Steatosis adversely impacts mitochondrial function by lowering mitochondrial membrane potential, leading to enhanced cell damage during cold ischemia and ischemic reperfusion injury.³⁷ The surgeon can suspect steatosis based on visual inspection and palpation. If the steatosis of the donor liver is not clear, then an additional frozen section can be obtained to make the final decision. Steatosis is the most common reason for rejecting the donor liver.^38,39 Depending on the degree of fat accumulation in the liver, steatosis is classified as mild (<30%), moderate (30–60%), or severe (>60%). As a general opinion, it is considered that a graft with severe steatosis is rejected and a graft with mild steatosis is accepted. Grafts with moderate steatosis should be considered in combination with other risk factors, such as advanced donor age and prolonged CIT, to ensure good outcomes.

Deranged Liver Function Tests

Derangement in liver function tests (LFT) is commonly seen in brain-dead patients, and these are usually due to steatosis, sepsis, and/or hemodynamic instability. The main concern is whether abnormal LFT will affect graft function. There is no upper limit of transaminase beyond which liver donation is contraindicated. The potential donor should not be rejected solely on the basis of an abnormal LFT. There may be underutilization of grafts based on transaminase elevations. In a retrospective cohort study of the UNOS data, while peak alanine aminotransferase (ALT) levels and trends were associated with the utilization of potential livers, there was no increased risk of graft failure based on peak ALT levels. This may represent an area to expand the donor pool.⁴⁰ It is worth stating that one needs to look at bilirubin, enzymes, and lactate trends with resuscitation to determine whether or not the organ can be used rather than any single value.

Cold Ischemia Time

Prolonged CIT is a risk factor for delayed graft function and primary nonfunction.⁴¹ A CIT of more than 10–12 h is associated with adverse outcomes. In grafts with steatosis or from elderly patients, further minimizing the CIT to less than 8 h has shown improved outcome.^42,43

Hepatitis C Positive Donors

Donors with hepatitis C virus (HCV) and detectable HCV RNA in their blood universally transmit HCV to the recipient.⁴⁴ Hence, utilizing HCV-positive allografts for HCV antibody-negative recipients or HCV antibody-positive recipients with an undetectable viral load is usually not advocated. Directly acting antivirals have changed the landscape of the management of HCV-infected patients. There have been numerous reports of successful outcomes following transplantation from an HCV antibody-positive donor to an HCV antibody-positive recipient.^45,46 Provided the donor liver does not have significant fibrosis, good outcomes can be achieved from HCV antibody-positive allografts, and such organs should not be automatically discarded.^47,48 In the West, HCV antibody-positive donors are usually young intravenous drug abusers with minimal liver fibrosis, whereas in India, they are usually older with fibrotic livers. That is why such donations are very rare in our country.

Donors with Hepatitis B Core Antibodies

It is well known that hepatitis B core antibody (HBcAb)-positive grafts have the potential to transmit hepatitis B virus (HBV) to hepatitis B surface antigen (HBsAg)-negative recipients.⁴⁹ There are reports suggesting poor outcomes when using grafts from HBcAb-positive donors, as the graft quality may be suboptimal.^50,51 Also, when organs from HBcAb-positive donors are used, there is a risk of reactivation and uncontrolled replication of HBV after transplantation due to immunosuppression, resulting in adverse clinical outcomes. However, with the availability of nucleos(t)ide analogs and hepatitis B immunoglobulin, the incidence of de novo HBV infection can be reduced. Recent reports have shown encouraging results when using HBcAb-positive donors, and HBcAb-positive status should not be the only reason to reject a donor liver.^52,53

Donors with Bacteremia and Infections

Historically, donations from bacteremic donors have been considered a relative contraindication for donation. The United Nations Organ Sharing (UNOS) database has reported lower graft survival when using bacteremic donors.⁵⁴ Thus, caution needs to be exercised when using donors with sepsis. However, the incidence of infection transmission from a bacteremic donor to a recipient is low. Some transplant centers have been using DD from bacteremic donors to expand the donor pool with good transplant outcomes.^55,56 While accepting donors with bacteremia, it is important to keep in mind that the source of sepsis should be remote from the liver, the donors should be under appropriate and sensitive antibiotic cover, ideally for 24–48 h, and organs from donors with multi-drug-resistant sepsis must be avoided except in exceptional circumstances.

In a tropical country like India, the transmission of infections like dengue, malaria, and hydatid from the donor to the recipient also needs to be considered. Donor-to-recipient transmission via organ transplantation of dengue and malaria has been reported.^{57, 58, 59, 60, 61, 62} It is important to suspect and screen for these infections. While transplantation of a liver graft with hydatid disease is controversial, there are reports of the use of liver grafts with hydatid disease in urgent liver transplantation.^63,64

Donors with COVID-19

Given the COVID-19 pandemic, testing for COVID-19 in the donor is standard practice. However, the risk of blood stream-related transmission of the disease is questionable, and there are no evidence-based guidelines for non-lung solid organ transplantation from SARS-CoV-2-positive donors. A systemic review identified sixty-nine recipients of non-lung organs from SARS-CoV-2-positive donors, which included 18 liver transplant recipients. Transplantation of organs other than the lungs from SARS-CoV-2-positive donors seems to be a safe practice with a low risk of transmission. They found no documented case of donor-derived infection in non-lung organ transplantation. In case organ donation from a SARS-CoV-2-positive donor is contemplated, it appears pragmatic to consider donors with low viral replication (Ct > 30) at procurement.⁶⁵

Donors with HIV Infection

Due to the HIV epidemic, there are a large number of DDs with HIV who can potentially donate organs to recipients living with HIV. Due to advances in HIV management, HIV has gone from being considered a dreaded disease with high mortality to a chronic disease that can be managed with medical therapy. In the United States, donations from HIV-positive donors were banned until 2013, when this ban was lifted after the passage of the HIV Organ Policy Equity Act, allowing donations to an HIV-positive recipient.⁶⁶ Some concerns regarding organ donation from HIV-positive donors include the transmission of drug resistance and HIV superinfection in recipients. Data on liver transplants using HIV-positive donors is scarce. However, data from kidney transplantation suggests favorable outcomes.⁶⁷

Donors with Malignancy

Due to the potential for transmission of donor-derived malignancy to the recipient, donors with a history of malignancy are usually excluded from liver donation. However, donors with a history of treated malignancy or low-grade primary malignancy can be considered for liver donation to expand the donor pool. The available reports show a very low risk of transmission of donor-derived malignancies by the donor organ.^{68, 69, 70} Donors with metastatic malignancy, including regional lymph node metastasis, should not be used due to the high risk of tumor transmission. Donors with active malignancy are excluded; an exception to this rule are donors with nonmelanoma skin cancer and low-grade primary CNS tumors (Grade I and II), as such tumors have a low metastasis potential. Donors with CNS tumors should be excluded from donation if the tumors are high grade (Grade III or IV) or there is a history of ventriculoperitoneal shunts, prior craniotomies, systemic chemotherapy, and/or cranial radiotherapy.⁷¹ Donors with a history of treated malignancy can be considered for organ donation, and the risk of transmission of malignancy is generally regarded as low, with a long interval between diagnosis of malignancy and organ donation. However, a detailed evaluation for recurrence of the malignancy should be made before considering such patients as organ donors.⁷² About 2–4% of donors are known to have either a current or past history of malignancy. Various groups have attempted to stratify donors with malignancy as per their risk of transmission of malignancy to the recipient.^{73, 74, 75, 76} The risk of donor-transmitted malignancy from a prospective donor with present/past malignancy is summarized in Table 4. However, it should be noted that the risk stratification is not absolute, and the decision regarding accepting a donor should be determined on a case-by-case basis, considering the type of cancer and its stage along with a disease-free interval. The potential risks and benefits of accepting a deceased donor with malignancy should be weighed against the risks of waiting for another donor and the urgency of the transplant.

Table 4.

Risk Stratification for Donor Transmitted Malignancy.

Unacceptable risk	•Donors with active malignancy (except non-melanoma skin cancer and low-grade primary CNS tumor) •Any tumor with metastasis, leukemia, lymphoma, plasmacytoma, sarcoma, renal cell carcinoma with extension beyond kidney, choriocarcinoma, thyroid medullary and anaplastic Cancer
High risk	•Invasive breast cancer, lung Cancer, melanoma, oesophageal/gastric/pancreatic/liver and biliary Cancer, neuroendocrine tumor, oropharyngeal cancer, ovarian cancer, prostate cancer with extra prostatic extension
Intermediate risk	•Colorectal cancer without lymph node or distant metastasis with disease free survival >5 years, breast cancer Stage 1a, grade 3 and 4 CNS neoplasia, thyroid solitary papillary carcinoma and invasive follicular carcinoma
Minimal risk	•Non melanoma skin cancer, prostate cancer (confined to prostate), WHO Grade I and 2 CNS neoplasia, renal cell cancer <1 cm (T1a)

CNS, central nervous system, WHO, world health organization.

Donors with Blunt Liver Trauma

Given the organ shortage, brain-dead donors with recent liver trauma also represent a potential source of liver allografts that should be considered. A recent audit of the French registry data reported 142 LTs from donors with recent liver trauma. Specific liver trauma management was needed during transplantation in 19 (13%) patients [local hemostatic control (n = 15), partial hepatic resection on the back table (n = 3), or perihepatic packing (n = 1)]. The one-year overall and graft survival rates were 85% and 81%, respectively, while the 5-year rates were 77% and 72%. This suggests that using liver grafts from donors with recent liver trauma appears safe and acceptable.⁷⁷

Donor Risk Indices

In 2006, a donor risk index (DRI) was developed by Feng et al. 2²¹ to objectively predict graft survival in recipients by identifying seven donor factors that influenced transplant outcome/graft survival in recipients. DRI can be easily calculated using an online calculator (https://gastro.cchmc.org/calculators/donor-risk-index). A DRI of >1.7 is classified as a high-risk donor liver and is potentially associated with an increased risk of allograft failure. Subsequently, other scores to assess donor risk have also been developed.^{25,78, 79, 80} However, none of these can be extremely accurate and predict donor-recipient matching. They continue to be useful, especially in situations where extended criteria donors are used to make an objective decision regarding the use of graft and match it with its intended recipient.

Evaluation of Living Donors

Considering the scarcity of DD organs, there is a need for LDLT to save lives in advanced liver disease. Asian countries, including India, have developed significant expertise in LDLT over the years. LDLT is more commonly performed in Asia, and more than 90% of liver transplants in Asia are LDLT compared to the West, where more than 90% of liver transplants are DDLT.⁸¹ Most LT centers have evolved their protocols for donor evaluation in LDLT. While these protocols may have subtle variations, they are centered around ensuring donor safety. Many donors evaluated for LDLT do not proceed towards donation, which is donor-related in more than two-thirds of cases, including donor reluctance, low liver attenuation index, anatomic variations, unacceptable liver biopsy, and inadequate graft or remnant liver volume.

The prospective living liver donor should be evaluated for physical and mental fitness to undergo the hepatectomy; the liver anatomy of the donor should be assessed, and the potential risk for the recipient from the donor graft should be kept in mind. In LDLT, donor safety is of utmost importance, and thus a critical assessment of donor physical and mental health is critical. The donor should not be coerced to donate his organ and should also understand the potential risks of undergoing hepatectomy and its possible long-term consequences. Living donors are usually between 18 and 60 years of age,^82,83 with many centers accepting an upper age limit of 55 years. The majority of liver transplants that are performed are ABO blood group (ABO)-compatible. However, an ABO -incompatible transplant can be carried out in exceptional circumstances if an ABO-compatible donor is unavailable. ABO-incompatible transplants have shown acceptable outcomes in recent metanalysis.^84,85

Donors should not be suffering from liver disease or comorbidities, such as coronary artery disease or cerebrovascular disease, and have a body mass index (BMI) of less than 30. Obese patients are likely to be excluded from donation due to a higher risk of postoperative complications as well as a higher risk of hepatic steatosis. The basic criteria to assess if the donor is fit for the liver donation surgery are shown in Table 5. After ascertaining donor fitness to undergo liver transplant surgery, reviewing the donor imaging for the liver volumetry and the vascular and biliary anatomy is essential. Some factors that need consideration while selecting a donor for LDLT are described below.

Table 5.

Criteria for an Acceptable Donor in Living Donor Liver Transplantation.

•Volunteer donor who is related/emotionally attached to the recipient, understands the potential risks of undergoing hepatectomy, and will be compliant with follow-up

•Age range 18–55 years

•No known medical disease that would increase perioperative risk

•No risk of disease transmission from donor to recipient

•ABO compatible except in exceptional circumstances

•An adequate partial liver graft can be safely harvested

Donor Age

While there is no absolute cut-off for age for liver donation, elderly donors may have a greater risk of perioperative complications and should have a more rigorous evaluation. Donors should preferably be between 18 and 55 years of age. In a worldwide survey of live liver donor selection policies at 24 centers with a combined experience of 19,009 adult living donor liver transplants, Soin et al.⁸⁶ found that while the upper age limit of donors varied between 50 and older than 60 years, more than half the centers accepted donors older than 60 years of age. However, data suggests that the outcomes and long-term graft survival of adult liver transplantation involving elderly living donors may be worse.^{87, 88, 89, 90, 91}

Donor Obesity

Obese donors are likely to have hepatic steatosis and are also at increased risk of perioperative complications. Donors with a BMI > 30 need a liver biopsy or magnetic resonance imaging (MRI) fat detection because of the increased risk of steatosis and nonalcoholic steatohepatitis. Most centers reject donors with a BMI> 35, and many centers do preoperative donor liver biopsies if the donor's BMI is > 28–30.⁸⁶ Prospective obese liver donors should be advised to lose weight before donation. Some centers have a protocol to get a non-contrast computerized tomography (CT) abdomen to look at the liver attenuation index (LAI), andthere is severe steatosis and if there is no urgent requirement for liver transplant in the recipient, advise the obese prospective donor to reduce body weight before donation, or if transplantation is urgently required, perform a liver biopsy to assess steatosis/steatohepatitis.

Donors with Medical Diseases

Donors with medical diseases that would increase perioperative risk are a contraindication to liver donation. Well-controlled hypertension without end-organ damage can be considered for living liver donation. Donors with diabetes mellitus (DM) can be considered for living liver donation if they are well-controlled and have no end organ damage or other risk factors like obesity, hypertension, or hyperlipidemia. Hyperglycaemia has been shown to have a negative impact on liver regeneration. Also, DM is associated with impaired liver microvascular circulation, which makes these grafts more susceptible to ischemic injury during transplantation.⁹² Due to these factors, DM in donors remains controversial for liver donation.

Donors with infections or malignancies that may be transmissible to the recipient should not be considered for live liver donation. Hepatitis B virus core antibody-positive patients with undetectable HBV DNA have been shown to have good post-transplant outcomes if the recipient is maintained on antiviral treatment post-transplant. HCV antibody-positive donors who are HCV RNA-negative can also be considered for living liver donation. Donors who have been successfully treated for malignancy in the past can be considered for living liver donation on a case-by-case basis, as discussed above for DD. Hypercoagulable states should be tested for (i.e., factor V Leiden, prothrombin mutation G20210A, anti-thrombin III and protein C and S deficiency, antiphospholipid antibodies, homocysteine).⁹³ Hypercoagulable states are relative contraindications for donation due to the fear of increased donor mortality/morbidity from portal vein or hepatic artery thrombosis and pulmonary embolism.

When the liver disease in the recipient is due to a genetic cause, adequate evaluation should be done to exclude the genetic disease in the potential donor if the donor is a blood relative.⁹⁴ In a monogenic disorder like Wilson disease, the mutation in the recipient should be identified so that the same can be tested in the related donor. There are reports from Japan and China on donors who were heterozygous for the Wilson genetic defect showing a favorable post-transplant outcome in recipients, comparable to transplant outcomes from nonheterozygote donors with no risk of recurrence.^{95, 96, 97} Similarly, the majority of inherited disorders of metabolism are inherited in an autosomal recessive fashion, in which case parents are obligate carriers of the mutation. Heterozygous related liver donors of patients with inherited metabolic disorders have also reported acceptable outcomes with no negative impact on either the donor or the recipient.^{98, 99, 100}

Stepwise Evaluation of Target Donor

As some of the donors initially assessed may be unfit for liver donation, the evaluation should be done stepwise to reduce the cost. After selecting the target donor, blood type and crossmatch compatibility are checked at the outset. A thorough medical history and examination should be obtained to assess for systemic illness, autoimmune disorder, bleeding/clotting disorder, hematological disorder, or malignancy. A history of smoking, alcohol, and illicit drug use should be obtained. The donor evaluation protocol is depicted in Table 6.

Table 6.

Donor Evaluation Protocol in Living Donor Liver Transplantation.

Phase 1: •Counseling, explaining risks, and assessment of motivation of the donor •History of illness and addictions and clinical examination •Blood grouping •Basic hematological and biochemical tests, including liver function tests, PT •Serology: HBsAg, Anti-HCV, HIV, VDRL, IgG Anti HBc •Pregnancy test in women if < 50 years of age •Imaging: Ultrasound of abdomen, elastography, X-Ray chest •Triple-phase CT abdomen to assess LAI, vascular anatomy, and volumetric assessment •MRCP to assess biliary anatomy

Phase 2: •HBV DNA and Anti-HBs if Anti HBc positive •CMV IgG •ANA, AMA, ASMA •Thyroid function tests •HbA1c •G6PD •APTT •PSA (for males) •Urine routine examination •ECG, X-Ray chest PA view, 2D ECHO (<35 years), DSE (>35 years) •Pulmonary function tests if smoker, asthma or age >40 years •Tests for hypercoagulable state •Psychiatrist evaluation

For female donors •CA125 (for age >35 years) •Ultrasound pelvis or trans-vaginal ultrasound •Papanicolaou (PAP) smear for married women •Mammography (for age >35 years), gynecological clearance •Gynecology clearance

Donor acceptance •HLA typing •Pre-anesthetic check-up •Informed video consent •Approval by the authorization committee

Anti-HCV, antibodies to hepatitis C; APTT, activated partial thromboplastin time; CA, carbohydrate antigen; CEA, carcinoembryonic antigen; CECT, contrast-enhanced computed tomography, CMV, IgG cytomegalovirus immunoglobulin G; DNA, deoxyribonucleic acid; DSE, dobutamine stress echocardiography; ECG electrocardiogram; ECHO, echocardiography, HBcAb hepatitis B core antibody; Anti-HBs, hepatitis B surface antibody; HIV, human immunodeficiency virus; HLA, human leukocyte antigen; LAI, liver attenuation index; MRCP, magnetic resonance cholangiopancreatography; PSA, prostate-specific antigen; PT, prothrombin time; VDRL, venereal disease research laboratory.

Initial Assessment

Initial tests include basic hematological and biochemical tests, serology for infections (HBsAg, Anti-HCV, HIV, VDRL, and IgG anti HBc), and ultrasound of the abdomen. For women with childbearing potential, a pregnancy test isperformed. A triple-phase computerized tomography (CT) abdomen is done to assess for liver steatosis, vascular anatomy, and volumetric status. Steatosis of the liver is evaluated on a plain CT abdomen by calculating the LAI. The information from the CT scan for donor assessment is given below.

Initial Assessment by Computerized Tomography/MRI in Potential Living Donors

• (i) Steatosis assessment

It has been hypothesized that every percentage increase in fat in the donor graft decreases the functional mass of the liver by 1% and may also disrupt microcirculation.¹⁰¹ The normal liver has a higher attenuation than the spleen on an unenhanced CT scan. LAI is used for hepatic steatosis assessment. LAI is calculated by placing a circular region of interest of at least 1 cm² at multiple places on the liver and the spleen and calculating the difference between the mean hepatic attenuation and the mean splenic attenuation. The attenuation value of a normal liver is approximately 50–57 Hounsfield Units (HU), which is around 10 HU more than that of the spleen.¹⁰² LAI values of >5 predict the absence of significant macrovascular steatosis; LAI values of - 10 to 5 HU suggest mild to moderate steatosis (6–30%), while LAI values of less than - 10 HU indicate moderate to severe hepatic steatosis (i.e.,≥30% fat). LAI values of 5–15 are acceptable, while donors with LAI values of less than −10 are not acceptable for liver donation. Donors with LAI values of −10 to 5 need further evaluation by liver biopsy.¹⁰³ Although donation policies vary across centers, potential living donors with ≥33% macrosteatosis are declined, and many centers prefer to restrict the donation to donors with less than 10% steatosis.¹⁰⁴ Given the invasive nature of liver biopsy with its potential adverse events (pain, bleeding, and death) and inconsistent results due to the nonuniform/patchy nature of steatosis, noninvasive methods to assess liver steatosis are preferred at many centers.¹⁰⁵ Transient elastography with a controlled attenuation parameter (CAP) using a Fibroscan® device is a valuable tool to assess liver fibrosis and steatosis. However, there is a need for further studies to establish its role in the preoperative evaluation of liver grafts before organ procurement.¹⁰⁶ MRI-based techniques appear promising in the evaluation of hepatic steatosis. Both magnetic resonance elastography (MRE) and magnetic resonance imaging-estimated proton density fat fraction (MRI-PDFF) have been shown to correlate with liver biopsy and may do away with the need for a liver biopsy.^{107, 108, 109, 110} MRI PDFF fares better than ultrasound based CAP measurement (AUROC of 0.85 for CAP vs. 0.99 for MRI-PDFF).¹¹¹ Due to the high accuracy and noninvasive nature of MRI-PDFF, it is quickly becoming the most preferred mode of steatosis evaluation at most centers. If a liver transplant can wait, potential donors with steatosis are advised to lose weight and then be reassessed with a repeat unenhanced CT scan.¹¹²

• (ii)Volumetric assessment

To assess whether the planned graft volume will be sufficient for the recipient, can be calculated by the graft-to-recipient body weight ratio (GRWR), in which the estimated graft volume is used instead of the actual graft weight [estimated GRWR = (graft volume/recipient body weight) x 100)].¹¹³ The optimal GRWR should be greater than 0.8. GRWR should not be less than 0.8% to avoid small-for-size syndrome and early graft failure. In recipients with good functional status and minimal portal hypertension, a lower GRWR of up to 0.6 is acceptable by most liver transplant centers. Alternatively, the graft requirement can be calculated using the graft volume (GV) to recipient standard liver volume (SLV) %. While various formulas have been developed to predict the SLV^{114, 115, 116} it has been shown that all formulas may not be accurate in a particular patient population. None of these formulas are precise for SLV estimation in the Indian population.¹¹⁷

To prevent postoperative hepatic insufficiency, the functional liver remanent (FLR) volume of the donor should not be less than 30% of the initial volume. However, the acceptable FLR should be > 35–40% in older donors and donors with steatosis, considering the decreased physiological liver reserve of the donor liver.¹¹⁸

Left-lobe grafts have reduced donor morbidity but have lower volumes, while right-lobe grafts have higher donor morbidity. While left lobes were initially only used for babies, experience over the past decade has validated their use in adults with less severe grades of portal hypertension who meet GRWR criteria.¹¹⁹

• (iii)Anatomical evaluation (Vascular and Biliary)

The hepatic artery, portal vein, and hepatic vein anatomy should be amenable to reconstruction in the recipient with no compromise to the safety and vascularity of the donor. Preoperative magnetic resonance cholangiopancreatography (MRCP) is done to delineate biliary anatomy, which is further confirmed with Intraoperative cholangiography (IOC) routinely in almost all liver transplant centers. The types of grafts that are harvested in LDLT include the right lobe, left lobe, and left lateral segment grafts. The type of hepatectomy is guided by the estimated graft and remnant liver volumes as well as the vascular and biliary anatomy. The imaging allows the identification of aberrant vascular anatomy or biliary anomalies, which can guide the surgeon.

Further Evaluation if the Computerized Tomography of a Potential Living Donor is Acceptable

If the donor is acceptable after the initial evaluation and CT assessment, further detailed evaluation of the prospective donor is carried out, which includes autoimmune markers (anti-nuclear antibodies, antimitochondrial antibodies), tests for hereditary hemochromatosis screening (iron, iron-binding capacity, ferritin), alpha-1-antitrypsin level, the status of the G6PD enzyme, etc. In males >40 years of age, PSA is done. Further tests to screen for potentially transmissible disease include cytomegalovirus (CMV IgM and IgG), Epstein-Barr virus (EBV IgM and IgG), and HBV DNA in prospective donors who are IgG anti-HBc positive. Further targeted evaluation is done as required, e.g., for patients with a family history of Wilson disease. Chest radiographs, electrocardiograms, and echocardiography are done in all patients. The International Liver Transplant Society (ILTS) recommends a thorough cardiovascular assessment (echocardiography should be done in all patients, and if necessary, stress echocardiography and/or coronary angiography may be done). ILTS also recommends screening for asymptomatic inherited coagulation disorder.¹²⁰ A thorough psychiatric evaluation of the donor should be carried out before liver donation. There are ethical issues in accepting donors with psychiatric disabilities, as there are concerns about the donor's capacity to make decisions and the possibility of the donation affecting the donor's psychiatric illness. Informed consent should be obtained after explaining the surgical, medical, financial, and psychological risks of undergoing hepatectomy.

Biopsy of Donor Graft

Liver steatosis and abnormal liver function tests (LFT) are the most frequent reasons for carrying out a liver biopsy in donors. Pretransplant donor biopsies are not usually required in LDLT. A report from a single center has shown that liver biopsy is frequently abnormal despite normal LFT and radiological findings. They showed that 5.6% of apparently healthy liver donors had non-steatosis liver pathologies in the biopsy that contraindicated transplant.¹²¹ Some centers routinely carry out preoperative donor biopsies for this reason. With newer imaging techniques, such as MRI quantification of hepatic steatosis, we can now accurately exclude significant liver steatosis, thus obviating the need for a liver biopsy to rule out significant steatosis.¹¹⁰ Besides donor steatosis, pretransplant liver biopsies in potential living donors are carried out if there is a history of alcohol abuse, the liver biochemical tests are elevated, or to exclude a hereditary condition in a donor. The indications for liver biopsy are depicted in Table 7. The disadvantage of a liver biopsy for a potential liver donor is that the positive yield of the biopsy is low and there is a risk of complications, including bleeding.

Table 7.

Indications for Liver Biopsy in a Donor.

Donor dependent	History of significant alcohol use Abnormal liver biochemistry tests Obese donors, abdominal imaging suggesting steatosis. Anti-HBc positive donor with equivocal fibrosis on elastography
Recipient dependent	Hereditary liver disease in recipient (to exclude occult hereditary liver disease in donor)

HBc, hepatitis B core.

An algorithm for the evaluation of living donors is depicted in Figure 1. Some common reasons for the non-maturation of potential liver donors after preliminary consent and screening are donor reluctance, fatty liver, inadequate remanent liver volume, psychosocial reasons, hypercoagulable state, anatomic variations, and poor pulmonary functions.

Figure 1.

Algorithm for evaluation of potential live donor.

Donor evaluation is a critical step in liver transplantation. Appropriate graft selection will achieve adequate functional regeneration, ensuring optimal graft function and survival. Thus, it is imperative to assess and evaluate donors for potential factors that are known to influence graft outcomes in recipients.

Credit Authorship Contribution Statement

Pankaj Puri, Conceptualization, writing, review and editing.

Abhinav Kumar, Writing of manuscript.

Mohd Qaleem, Writing of manuscript.

Conflicts of interest

The authors have none to declare.

Funding

None.