Algorithmic Approach to Deranged Liver Functions After Transplantation

Abstract

Liver transplant (LT) recipients require close follow-up with regular monitoring of the liver function tests (LFTs). Evaluation of deranged LFT should be individualized depending upon the time since LT, peri-operative events, clinical course, and any complications. These derangements can range from mild and asymptomatic to severe and symptomatic elevations requiring expedited personalized assessment and management. Pattern of LFT derangement (hepatocellular, cholestatic, or mixed), donor–recipient risk factors, timing after LT (post-operative, 1–12 months, and >12 months since LT) along with clinical context and symptomatology are important considerations before proceeding with the initial evaluation. Compliance to immunosuppression and drug interactions should be ascertained along with local epidemiology of infections. Essential initial evaluation must include an ultrasound abdomen with Doppler to rule out any structural causes such as biliary or vascular complications apart from focussed laboratory evaluation. Early allograft dysfunction, ischemia reperfusion injury, small-for-size syndrome, biliary leaks, hepatic artery, and portal vein thrombosis are usual culprits in the early post-operative period whereas viral hepatitis (acute or reactivation), opportunistic infections, and recurrence of the primary disease are more frequent in the later period. Graft rejection, biliary strictures, sepsis, and drug induced liver injury remain possible etiologies at all times points after LT. Initial evaluation algorithm must be customized based on history, clinical examination, risk factors, and pattern and severity of deranged LFT. Allograft rejection is a diagnosis of exclusion and requires liver biopsy to confirm and assess severity. Empirical treatment of rejection sans liver biopsy is discouraged.

Liver transplantation (LT) is the treatment of choice for patients with end-stage stage liver diseases.1, 2, 3 Furthermore, refinement in technique, growing experience, and improved post-operative critical care have made LT a feasible and effective option in patient with acute and acute-on-chronic liver failure.4, 5, 6, 7, 8 During follow-up, finding of deranged liver function tests (LFT) may be encountered at various time-points after LT. Such derangements can range from transient innocuous elevations to severe and persistent elevations that require urgent assessment and interventions to save the graft. The evaluation should follow a customized stepwise approach. It is imperative to keep in mind the pattern and severity of LFT derangement, peri-operative events, time since LT, donor and recipient factors, local epidemiology of infections, and drug history while evaluating deranged liver functions as they guide the initial approach significantly.9, 10, 11, 12, 13 The etiology of deranged LFT in the early perioperative period is usually distinct from that in the late post-LT period.^14,15 In this review, we will discuss various possible causes of deranged LFT at various given time points after LT, delineate possible risk factors, and outline a pragmatic approach to evaluate these patients.

Initial approach to the deranged LFTs

Various components of LFT and their significance are elaborated in the supplementary data. LFTs are usually done more frequently in the early post-transplant period (daily to weekly) and less frequently in the late post-transplant period. Abnormalities in the LFT can vary in symptomatology and severity. Most patients presenting to the outpatient services with deranged LFT are either asymptomatic or have vague non-localizing symptoms.^14,16 However, some may land up in emergency with myriad of acute symptoms and signs such as fever, acute abdominal pain, progressive jaundice, altered behavior, features of cholestasis, or portal hypertension which may help in generating initial differential diagnosis.^12,16,17 A mental map of the clinical background, pattern, magnitude of liver enzyme elevations, time since LT, and basic disease for which LT was done must be made prior to initiating evaluation.^9,10,16,17 Baseline values and the expected changes after LT should always be taken into consideration. Transient elevations in LFT can be seen in the first few days to weeks after transplantation due to surgical trauma, ischemia reperfusion injury (IRI), hemolysis, or drug-induced liver injury (DILI) which requires close follow-up. However, persistent or rising trend of LFT may indicate a serious issue mandating specialist evaluation.^18,19 Acuity of clinical presentation guides the initial approach. Evaluation should continue along with appropriate resuscitative measures.^10,12,16

History and clinical examination

There is considerable overlap in the presenting clinical features amongst the various possible etiologies of deranged LFT after LT. Most patients are asymptomatic and are picked up during routine follow-up. However, symptomatic patients most commonly present with reduced appetite, fever, jaundice, and/or pain abdomen.^9,10,14 Jaundice along with pruritis should prompt investigations for cholestatic causes. Clay-colored stools, steatorrhea, or signs of fat-soluble vitamin deficiency develop late and point towards a cholestatic etiology.^12,16

Donor risk factors, pre-LT recipient clinical status, and intraoperative events are important considerations, especially in the early post-LT period (<6 weeks)^9,18 and are outlined in Table 1. Operation notes should be carefully reviewed to gather accurate information regarding total operation time, the number of blood transfusions, dose of inotropes, cold ischemia time (CIT), warm ischemia time (WIT), graft to recipient weight ratio (GRWR), biliary anatomy and anastomosis, and vascular anatomy and anastomoses.^18,20,21 When evaluating deranged LFT in the later post-LT period, history of travel (especially to hepatitis A/E endemic areas), non-compliance to immunosuppressive medications, etiology of liver disease prior to LT, changes in the body weight, and alcohol recidivism should be elicited.^9,14,16 Further detailed review of any newly added drugs, their interactions, and use alternative medicines should be undertaken during history taking. Most importantly, apart from etiologies specific to LT recipients, usual causes of deranged LFT in the general population must always be in the differential diagnosis.^12,14,16 Time since LT helps in narrowing down differentials during the initial approach, however, it is not inviolable. Clinical judgment and context are paramount as many etiologies can co-exist and not necessarily follow any time bound incidence.10, 11, 12^,14

Table 1.

Risk Factors for Early Allograft Dysfunction After Liver Transplantation.

Donor related	Recipient related	Procurement related
Advanced age Macrovesicular steatosis >30% Peak sodium level >155 meq/L Use of high-dose vasopressors Prolonged ICU stays CVA as cause of death	Re-transplantation Overall disease severity before LT: •MELD >30 •Use of high-dose vasopressors •Renal failure •Acute-on-chronic liver failure •Need of prolonged mechanical ventilation	CIT >12 h WIT >90 min DCD

CVA, Cerebrovascular accident; CIT, Cold ischemia time; DCD, Donation after circulatory death; ICU, Intensive care unit; LT, Liver transplantation; WIT, Warm ischemia time.

Identifying the pattern of LFT derangement

Baseline/previous LFT reports of the patient under evaluation should be sought. Population specific cut-offs, when available, should be utilized.22, 23, 24 Disproportionate rises in aspartate aminotransferase (AST) and alanine aminotransferase (ALT) are the biochemical hallmark of hepatocellular injury whereas disproportionate increases in the levels of alkaline phosphatase (ALP) and gamma glutamyl transferase (GGT)/5′-nucleotidase (5′-NT) suggest primary biliary epithelial injury.^12,14,16 Early rise in bilirubin is also typically noted in cholestasis, however, its absence does not rule it out. R value may be used to determine the pattern of liver injury. It is calculated by dividing the ratio of ALT and ULN (upper limits of normal) of ALT by ratio of ALP and ULN of ALP. R value ≥5 and ALT >2 times the ULN suggest hepatocellular injury whereas cholestatic injury should be suspected if R value is ≤2 and ALP >2 times the ULN. R value of <5 but >2 and ALT, ALP both >2 times the ULN suggest mixed hepatocellular-cholestatic injury.²⁵ Supplementary Table 1 and Figure 1 outlines various possible etiologies of deranged LFT based on pattern and time since LT.

Figure 1.

Algorithmic approach to deranged liver function tests after transplantation. AIH, Autoimmune hepatitis; AS, Anastomotic biliary stricture; CT, Computed tomography; DILI, Drug induced liver injury; EAD, Early allograft dysfunction; HAT, Hepatic artery thrombosis; HCC, Hepatocellular carcinoma; IRI, Ischemia reperfusion injury; LFT, Liver functions tests; LT, Liver transplantation; MRI: Magnetic resonance imaging; NAFLD, Non-alcoholic fatty liver disease; NAS, Non-anastomotic biliary strictures; PBC, Primary biliary cholangitis; PCR, Polymerase chain reaction; PNF, Primary non-function; PSC, Primary sclerosing cholangitis; PVT, Portal vein thrombosis; SFSS, Small for size syndrome; TCMR, T-cell mediated rejection; USG, Ultrasonography. ∗ Viral etiologies include hepatitis B, C, A, E and atypical and opportunistic infections/reactivations such as Cytomegalovirus and Epstein bar virus. Usually requires both serological tests (antibodies) and quantitative PCR and/or histological examination on individualized basis. ^# Role of autoimmune antibodies alone to diagnose de-novo AIH remains debatable. However, high titers of anti-nuclear antibodies (ANA), ASMA, AMA, Anti-LC1 and/or atypical anti liver-kidney cytosolic antibody (targeting Glutathione-S-transferase T-1) may help in making an early diagnosis of de-novo AIH.

Focused laboratory testing, imaging, and histological examination

After localizing the probable etiology as either liver parenchymal, vascular or biliary based on history, clinical examination, and LFT derangement pattern, further customized testing should be done. As a dictum, non-invasive evaluation should be performed first. Ultrasonography (USG) of abdomen with Doppler is the initial imaging modality of choice.^9,14 It should preferably be performed by a radiologist experienced in assessing post LT patients. In the Doppler examination, hepatic artery, portal vein, and hepatic venous outflow tract should be carefully examined with respect to their diameter, flow waveforms, flow velocity, and patency.^26,27 Further, especial emphasis should be given to any features of liver parenchymal damage (acute or chronic) or portal hypertension such as ascites. Presence of any intra or extrahepatic biliary dilatation, peritoneal thickening, space occupying lesions, collections, and/or regional lymphadenopathy should be carefully looked for.^10,14,28

If there is any evidence of biliary tract obstruction, detailed evaluation via either contrast enhanced dynamic computed tomography (CT) or magnetic resonance imaging (MRI) should be undertaken.^14,29,30 Endoscopic ultrasound (EUS) can be both diagnostic and therapeutic especially if there are any collections such as biliomas or abscesses.^31,32 When Doppler imaging suggests vascular thrombosis or stenosis, dedicated imaging in the form of an angiography should be immediately performed to assess the site, severity and to plan management.^28,30

In cases where biliary or vascular cause is ruled out after above evaluation, the causes of liver parenchymal damage should be sought.^11,12,14 Serum trough levels of immunosuppressive agents must be done to rule out suboptimal immunosuppression.³³ Possible viral causes including hepatitis B (hepatitis B surface antigen, IgM HBc antibody, HBV DNA quantitative), hepatitis C (anti HCV antibody, HCV RNA quantitative), IgM hepatitis A virus, IgM hepatitis E virus, and cytomegalovirus (CMV) DNA quantitative should be done as per clinical context and individualized basis.^11,15 If still etiology remains elusive, evaluation for autoantibodies (ANA, AMA, ASMA), and total immunoglobulin G levels can be done on case-to-case basis. Anti-hepatitis D virus antibody (endemic areas), EBV DNA quantitative (especially in pediatric LT recipients), and hepatitis E RNA levels may be done to complete work up in selected patients.^10,14

Despite all the above clinically guided investigations if a cause cannot be found out, an image guided liver biopsy is recommended.^10,14 Furthermore, liver biopsy is mandatory to diagnose suspected rejection, recurrent or de-novo autoimmune liver diseases, suspected DILI, and to ascertain fibrosis accurately, if needed.^{14,16,25,30,33,34} A liver biopsy can also be done at the outset if the treating hepatologist deems it necessary after the initial non-invasive evaluation.¹⁴ However, unexplained deranged LFT, whether cholestatic or hepatocellular, despite detailed work up should not be considered immune-mediated (rejection) without histological evidence and must not be subjected to “empirical” steroid pulse therapy.^33,34

In the following section, we will briefly discuss the possible causes of deranged LFT and approach to diagnose them at various time-points after LT and are also summated in Table 2.

Table 2.

Diagnostic Pointers and Line of Management of Various Causes of Elevated Liver Function Tests After Transplantation.

Differential diagnosis	Timing and clinical pointers	Diagnostic tests	Management approach
Ischemia reperfusion injury14,31	First week Hepatocellular pattern Donor-recipient risk factors	Clinical diagnosis Rule out structural causes	80% resolve with supportive management35 No long-term impact 10–20% may progress to EAD36
Early allograft dysfunction37,38	First week Moderate-massive rise in aminotransferases in hepatocellular pattern Presence of donor and recipient risk factors (Table 1) Suspect if: •Worsening negative base excess •Unresolving coagulopathy •Persisting synthetic dysfunction •Persistent hyperammonaemia •Reduced-pale bile in the drain, if present	Clinical diagnosis of exclusion Rule out structural causes Diagnostic criteria: Presence of ≥1 of the following parameters in the first week after the LT39 1. Total bilirubin ≥10 mg/dl or INR ≥1.6 on postoperative day 7, or 2. Aminotransferases >2000 U/L within the first week after LT.	Supportive management Plasma exchange on case-to-case basis. Complete resolution and liver regeneration eliminates risk of long-term adverse outcomes. Re-transplantation if progresses to primary non-function.
Hepatic artery thrombosis40,41	Overall incidence: 5–6% Early HAT: <14 days •Massive elevation in AST/ALT in hepatocellular pattern Late HAT: Later period •Ischemic, multifocal NAS-biliary strictures	USG Abdomen with doppler Confirm with Angiography (CT or MRI)	Early HAT: Surgical or IR guided revascularization/thrombolysis Late HAT: Biliary drainage Re-transplantation if above measures fail.
Biliary leak42, 43, 44	Incidence: 5–15% Mostly occur in the first 1–3 months. Can present as pain abdomen, fever, cholangitis, intraabdominal/cut surface collections	USG Abdomen and/or cross- sectional imaging (CT/MRI)	Image guided (USG/CT/EUS) drainage of collections ERCP and biliary stenting.
Portal vein thrombosis45, 46, 47	Incidence: 2–3% More common in early post-operative period but can occur later also. Hepatocellular pattern. Persistent or new onset portal hypertension (ascites, variceal bleeding)	USG Abdomen with doppler Confirm with dynamic cross-sectional imaging (CT or MRI)	Surgical or IR guided revascularization/stenting Anticoagulation
Small for size syndrome48,49,50	Living donor/split grafts. Risk factors: •GRWR <0.8 •Graft steatosis •Older donor •Sick recipient (MELD >30) with high portal pressures, Insufficient outflow Present as prolonged cholestasis and features of hepatic insufficiency	Diagnosis of exclusion Diagnostic criteria: •Bilirubin >10 mg/dl on POD7 and •Features of hepatic insufficiency such as intractable ascites, daily production of >1L ascites on POD28, persistent coagulopathy, and/or high-grade hepatic encephalopathy.	Supportive Rule out structural causes Splanchnic vasoconstrictors may be tried.51,52 Plasma exchange in selective cases
Anastomotic biliary stricture14,15,42	Incidence: 15–25% Living donor > Deceased donors Most present 2–6 months after LT Cholestatic jaundice with/without Cholangitis	Cross-sectional imaging (MRI)	ERCP and stenting
Rejection2,33,34	10–30% recipients develop rejection Acute TCMR: •Hepatocellular pattern •Early TCMR: 80%; most occur in first 90 days; >80% respond to treatment •Late TCMR: 11–20%; most occur later (>180 days); 20–40% may fail to respond to first line treatment. •Repeated early TCMR predispose to late TCMR and CR. Chronic TCMR (CR): •1–3% incidence •Cholestatic pattern •60–70% respond to treatment AMR: Suspect when TCMR does not respond to adequate treatment Limited data	Liver biopsy is mandatory to diagnose type of rejection, to assess its severity and to rule out other possible etiologies. Repeat liver biopsy not needed to ascertain response if biochemical improvement seen.	Mild acute TCMR: Increase in baseline immunosuppression Moderate-severe TCMR (early and late): Intravenous methylprednisolone pulse therapy, concomitant up titration of baseline maintenance immunosuppression CR: Shift from cyclosporin to Tacrolimus; addition of mTOR inhibitors AMR: Limited data; steroid boluses, DSA depleting strategies.
Recurrent autoimmune liver diseases53,54	Incidence at 5-years •AIH: 20–30% •PBC: nearly 20% •PSC: 15–20% Clinical presentation similar to pre-LT	Diagnostic criterion similar to pre-LT criteria. Liver biopsy for AIH, PBC and overlap syndromes MRI Abdomen for suspected PSC	Limited data Modulation of immunosuppression
NAFLD55,56	Overall incidence •Recurrent NAFLD: >80% •NASH/fibrosis in 20–25% •De-novo NAFLD: 20–30% Metabolic syndrome and immunosuppressive agents predispose.	Ultrasound Abdomen Liver biopsy	Lifestyle changes Manage risk factors and comorbidities Immunosuppression drug modulation

AIH, Autoimmune hepatitis; AMR, Antibody mediated rejection; CR, Chronic rejection; CT, Computed tomography; DSA, Donor specific antibodies; EAD, Early allograft dysfunction; EUS, Endoscopic ultrasound; ERCP, Endoscopic retrograde cholangiopancreatography; GRWR, Graft to recipient weight ratio; HAT, Hepatic artery thrombosis; IR, Interventional radiology; INR, International normalized ratio; LT, Liver transplantation; MELD, Model for end stage liver disease; MRI, Magnetic resonance imaging; NAFLD, Non-alcoholic fatty liver disease; NASH, Non-alcoholic steatohepatitis; NAS, Non-anastomotic biliary stricture; PBC, Primary biliary cholangitis; POD, Post operative day; PSC, Primary sclerosing cholangitis; SFSS, Small for size syndrome; TCMR, T-cell mediated rejection; USG, Ultrasonography.

Early post-LT period (<1 month)

Ischemia Reperfusion Injury

LFT are universally deranged in the immediate post-operative period due to hepatocyte damage resulting from IRI. IRI is a consequence of ischemia (both cold and warm), that occurs during organ acquisition, preservation and implantation.^14,31,35,36 IRI typically has a hepatocellular pattern of LFT derangement in which AST/ALT can range from mild-moderate elevations to even >1000 IU/ml. Aminotransferases usually peak within the first 48 h and then decline steadily over a week.^35,57 Canalicular enzymes, i.e., ALP, bilirubin, and GGT rise and fall slowly (7–14 days) than the aminotransferases.^9,10,18 IRI mostly resolves with conservative management and has no long-term impact on the graft and recipient. However, nearly 20% may progress to early allograft dysfunction (EAD) and/or primary non-function (PNF) especially if risk factors^14,36 are present as elaborated in Table 1.

EAD and PNF

Incidence of EAD and PNF has been reported between 15–30% and 2–10%, respectively.^14,37,38 Programs that use extended criteria donors and perform LT on sicker recipients are likely to have higher incidence.^21,37,58, 59, 60, 61 EAD affects both the short- and long-term outcomes in the form of higher chances of PNF, infections, biliary complications, rejection, and death.^21,60, 61, 62, 63 Criteria given by Olthoff et al.³⁹ are most commonly used to diagnose EAD (Table 2).

PNF is defined as allograft non-function that results in death or re-transplantation within first post-LT week whereas when progressive EAD leads to non-function resulting in mortality or re-transplantation after the first week but within first 30 days after LT, it is known as delayed PNF.^37,64 EAD and PNF are conceptually sequential and are diagnoses of exclusion.^20,37,64

Diagnosing EAD and PNF requires combined clinical, laboratory, and radiological evaluation. USG and doppler examination of biliary tree, hepatic artery, portal vein and venous outflow tract must be done to exclude structural causes such as hepatic artery thrombosis (HAT), portal vein thrombosis (PVT), hepatic venous outflow tract obstruction (HVOTO), and any biliary complications.^14,37,39 Small-for-size syndrome^65,48 (SFSS) and large for size syndrome⁶⁶ (LFSS) should also be ruled out along with hyperacute rejection^2,34 (rare). There are no histologic hallmarks suggestive of EAD apart from changes of IRI such as centrilobular hepatocyte swelling, hepato-canalicular cholestasis, periportal and perivenular congestion, hemorrhage, necrosis, and neutrophilic inflammation.^38,67

Small-for-Size Syndrome

SFSS is usually encountered when partial/split liver graft is unable to sustain metabolic demands of the recipient.^65,68 It is also a diagnosis of exclusion.⁴⁸ Endothelial and sinusoidal injury as a result of excess portal inflow is the underlying proposed pathophysiology.^68,69 Risk factors and diagnostic criteria^48,49,50 of SFSS are elaborated in Table 2. Meticulous pre-operative planning in the form of donor selection keeping in mind the recipient disease severity is the key to prevention.^61,50 Intraoperative portal inflow and outflow tract modulation may be undertaken on case-to-case basis.^65,49 Management is primarily supportive, which may include the use of splanchnic vasoconstrictors,^51,52 serial plasma exchanges, until graft regenerates enough to take over recipients' metabolic demands.^37,65,48

Large for Size Syndrome

LFSS is quite rare but can present as EAD almost exclusively in the pediatric LT recipients.^66,70 Recipients <10 kg and GRWR >4% are at higher risk.⁶⁶ Abdominal compartment syndrome, vascular caliber size discrepancies, inadequate portal circulation, and impaired tissue oxygenation are underlying propagators of LFSS. Pre-operative planning is key to prevention similar to SFSS.^66,70

Vascular causes

Hepatic Artery Thrombosis

HAT is a serious complication and can happen in the first 2 weeks after LT (early HAT) or in the later period (late HAT).^71,40 Reported incidence of HAT is around 5%.^40,41 It presents as severe graft dysfunction akin to PNF with extremely elevated aminotransferases in hepatocellular pattern.^40,72 Complex hepatic arterial anatomy, need of multiple arterial anastomoses, re-LT, and protracted surgical time are reported risk factors.^71,41,73 Doppler USG mostly clinches the diagnosis but needs to be confirmed via CT or MR angiography.73, 74, 75 Urgent revascularization via surgical revision or interventional radiologic intervention is crucial.^41,73,76 Late HAT, on the other hand, has more indolent presentation and can present during 1–12 months after LT with biliary complications as elaborated later^40,41,73,77 (Table 2). Diagnostic algorithm is similar to early HAT. Re-LT may be needed rarely.⁴⁰

Portal Vein Thrombosis

PVT affects approximately 2% of LT recipients and is more frequent in the early post-LT period. However, it may also occur in the later period.45, 46, 47 Most will present with mild-moderate rise in aminotransferases of a hepatocellular pattern. The features of portal hypertension (ascites or variceal bleeding) usually develop in long-standing cases.^14,45 Size mismatch (small portal vein size), pre-existing PVT, and hypercoagulable state are risk factors.^46,47 Anti-coagulation, intervention radiology-guided recanalization/stenting is the mainstay of management which when fails mandates surgical intervention.^45,78

Hepatic Vein/Inferior Vena Cava Stenosis

Hepatic venous or inferior vena cava stenosis usually results from technical anastomotic complications or rotation of the allograft and generally occurs in the first 3 months after LT.^46,47 The use of “piggyback technique” which involves preservation of the recipient inferior vena cava is also one of the risk factors.^45,79 Clinical presentation is similar to HVOTO such as progressive ascites, disproportionate leg edema, and deranged LFT.^79,80 Intervention radiology-guided recanalization/stenting can be performed in appropriate cases.⁸⁰

Biliary causes

Biliary complications remain the Achilles heel of LT and adequate preoperative evaluation of donor biliary anatomy with respect to the number, size, and variations is crucial.^31,42, 43, 44 Bile leaks and strictures are the most common biliary complications.^31,43,44 Bile ducts have only hepatic arterial supply and hence are prone to ischemic result, especially in the supra-duodenal segment of the common bile duct. Biliary complications can present with varied symptoms such as jaundice, cholangitis, pain abdomen, or intraabdominal collections with cholestatic pattern of deranged LFT in most patients.⁴² Conventionally they have been reported in 5–15% and 15–30% of deceased donor and living donor LT recipients,^44,81 respectively. There has been significant reduction in the overall incidence of biliary complications in the recent reports likely due to improved pre-operative imaging and surgical techniques.^31,42,44

In the early post-LT period, bile leaks are more common and can occur due to anastomotic site leak, leak from cut surface of the liver, accessory/aberrant ducts leaks, or due to an incidental injury.^42,43 In the later period, anastomotic strictures (AS) due to size mismatch are more frequent.^10,14,15,42 Non-anastomotic strictures (NAS) can result as a sequelae of ischemia (HAT, DCD, prolonged CIT/WIT, EAD), or immunological injury (ABO incompatibility, chronic rejection, recurrent primary sclerosing cholangitis).^42,82 Choledocholithiasis, sludge, and biliary cast syndrome usually present in the late post-LT period. Most bile leaks and AS can be managed with the help of endoscopic retrograde cholangiography (ERC) or percutaneous transhepatic biliary drainage (PTBD) and may not have any long-term negative impact on the graft and patient survival.^83,84 EUS is another valuable tool in the armamentarium for suitable patients now-a-days.^32,85 Unfortunately, NAS are difficult to manage due to multifocal and intrahepatic stricture and negatively impacts overall survival^73,42 (Table 2).

Allograft Rejection

There has been a tremendous reduction in the incidence of allograft rejection as a result of significant advances in the understanding of transplant immunology and post-LT immunosuppression regimens (especially the tacrolimus-based regimens).^2,33,34,86 Nonetheless, nearly 10–30% of LT-recipients have one or more episodes of rejection. It is uncommon in the first seven days after LT except for hyperacute rejection which is fortunately extremely rare now-a-days.^14,64,86 Most episodes occur within the first 90 days after LT.^86,87 However, rejection can happen at any time after LT. Overall, T-cell mediated rejections (TCMR, previously called acute cellular rejection) are much more common. Early TCMR usually occurs during the first 90 days following LT whereas late TCMR occurs more than 90 days after LT.^15,86 Most patients at presentation are either asymptomatic or have vague symptoms such as fatigue, decreased appetite etc. Especial emphasis on immunosuppression compliance and drug interactions is central to initial clinical assessment of a suspected rejection episode.^33,87 Rejection is a diagnosis of exclusion hence acute viral hepatitis, CMV hepatitis and recurrence of primary disease (especially after 1 year) along with any structural causes must be excluded first.13, 14, 15^,17,33 A liver biopsy is mandatory to diagnose an episode of rejection and also provides valuable prognostic information. Systematic and uniform reporting of liver biopsies using Banff schema assessing the extent, type, and intensity of portal inflammation, bile duct injury, hepatic and portal venulitis and endothelitis is imperative. Typical histological findings of rejection may be masked or under-reported in patients already on immunosuppression.^34,86

Early acute TCMR does not have any long-term adverse impact on graft and patient survival and more than 80% respond to methylprednisolone pulse therapy.^33,86 However, multiple episodes of early TCMR, non-compliance to immunosuppression, female gender, LT for autoimmune liver disease, younger age, CMV infection, and non-biologically related donor are some known predisposing risk factors for the development of late acute TCMR, which adversely affects graft and patient outcomes.^15,33,88 It has been shown previously that higher proportion (20–40%) of patients with late TCMR fail to respond to steroid pulse therapy with nearly one-fourth progressing to chronic TCMR (CR).^33,88

Overall incidence of CR is low (<5%) in adults but can be seen in up to 15% of pediatric recipients.⁸⁸ Furthermore, incidence of CR has significantly reduced in the tacrolimus era.^86,87 Bile duct loss affecting >50% ducts, or bile duct pyknosis/atrophy affecting majority of bile ducts with/without bile duct loss, and/or obliterative arteriopathy are the histological hallmarks of CR.³⁴ CR has been considered to have grave prognosis as 40–50% patients may progress to graft loss requiring re-LT.^33,88 Although, there is no strong evidence to guide treatment of CR, expert opinion-based recommendation is to shift from cyclosporine-based immunosuppression to tacrolimus-based immunosuppression. Recent evidence also supports adding or shifting to everolimus may abate CR in more than 50% cases.^33,86,89,90

Antibody-mediated rejection (AMR) is a rare (<1% overall) cause of LFT derangement and graft dysfunction in ABO-compatible LT.³⁴ It should be considered as a differential when patients with suspected TCMR does not responding adequately to the standard therapy.^33,91 According to the Banff criteria, a diagnosis of acute AMR is suggested by the presence of classic histologic features (endothelial cell hypertrophy, capillary dilation, leukocyte sludging, and edema), complement four-dimensional (C4d+) vascular staining, circulating DSA, and exclusion of other causes. Chronic AMR is another poorly defined and hence challenging differential. Histological features such as mild-moderate inflammation along with low-grade interface activity and fibrosis, C4d+ staining with the presence of circulating DSA in last 3 months suggest diagnosis of chronic AMR.³⁴ Data with respect to its incidence and management strategy are extremely scarce.^15,33

Infections

Infections occur in nearly one-third recipients during the initial post-LT period.^92,93 Post-LT infections can be donor or recipient derived and community acquired or nosocomial.^14,93 Bacterial infections are most common (50–70%) followed by viral (20–40%) and fungal infections (5–15%).^30,92,93 Whereas infections such as viral hepatitis, liver abscesses, and cholangitis directly involve the liver and present as deranged LFT along with other suggestive clinical features, systemic infections (sepsis) can also have deranged LFT which are mostly mixed or cholestatic pattern.^94,95 Infections follow a pattern of incidence with respect to time after LT depending upon the level of immunosuppression, hospital visits, interventions, and co-morbidities. These can help in narrowing the initial differential diagnosis as outlined in Table 3. However, infections (new or reactivations) can occur at any time after LT and must be in the differential diagnosis for all magnitudes and patterns of deranged LFT.^11,15,93

Table 3.

Risk Factors and Chronology of Possible Infectious Causes of Elevated Liver Tests After Transplantation.

	Salient features	Infections and possible agents
<1 month	Nosocomial pathogens Donor derived infections. Latent or active infections of the recipient. Typical signs of infections such as fever, and leucocytosis are dampened due to immunosuppression	Bacterial infections predominate There is shift towards infection with multidrug resistant organisms. Non-albicans Candida species more common among the fungal infections. Common infection sites include: •Surgical site/wound •intraabdominal abscesses •Vascular lines and urinary catheters •Lower respiratory tract C. difficile colitis
1–6 months	Opportunistic infections more common Reactivation of latent or transmitted infections can occur.	Opportunistic infections •Cytomegalovirus •Epstein bar virus •Herpes viruses •Tuberculosis •Toxoplasma •Cryptococcus •Pneumocystis carinii pneumonia Hepatitis B and C (reactivations > de novo) Fungal infections: increasing incidence of non-albicans Candida species and Aspergillus
>6 months	Reactivation of latent/transmitted infections can also occur Opportunistic infections can occur in recipients with poor graft dysfunction and multiple rejection episodes.	Community acquired infections Epstein bar virus related post-transplant lymphoproliferative disease Fungal infections: Candidaspp, Aspergillus Viral hepatitis A, E
Risk factors for infections in the post-transplant period
•Prolonged operation time or re-operation •Bilio-enteric anastomosis •Recipient disease severity and intensive care unit stay before LT •Recipient bacterial/fungal colonization •Need of renal replacement therapy •Donor intensive care unit stay •Net state of immunosuppression •Repeat rejection episodes- need of steroid boluses and higher net immunosuppression. •Repeated hospitalizations •Cytomegalovirus seronegative recipient and positive donor.

LT, Liver transplantation.

Viral hepatitis (both hepatitis B and C) can either occur de novo or reactivate (if adequate prophylaxis not given) and usually present with massive elevations in the aminotransferases similar to acute hepatitis A and E infections in the endemic areas.^10,14,15 Chronic hepatitis E can also develop in immunosuppressed LT recipients and can present as persistently low-grade elevation in the aminotransaminases.⁹⁶ CMV infection is another relatively common cause of abnormal LFT, especially in the first 3-months after LT.^97,98 Seropositive recipients (previous CMV infection) may have reactivation due to the immunosuppression whereas seronegative recipients who receive graft from a CMV-seropositive donor are at high risk of de novo CMV infection.^92,93,97, 98, 99 These recipients typically receive prophylaxis to prevent infection.⁹⁹ CMV infection can be asymptomatic or present with CMV syndrome or end-organ disease.^97,98 Apart from prodromal symptoms such as fever and malaise, moderate rise in aminotransferases in a hepatocellular pattern can be seen.⁹⁷ Nearly 90% recipients acquire Epstein–Barr Virus (EBV) infection in the childhood and remain seropositive. EBV-seronegative LT-recipients (pediatric LT) may acquire EBV in the first year and can present as febrile mononucleosis syndrome and hepatitis having a hepatocellular pattern of deranged LFT and may also present as post-transplant lymphoproliferative disorder.^{92,93,100,101}

Drug-induced Liver Injury

LT-recipients are usually on multiple medications of various classes especially in the initial 12 months. DILI may have either hepatocellular or cholestatic pattern.^{11,12,14,15,17} Temporal association of any newly added medication with onset of deranged LFT should be sought with detailed medication history with especial emphasis on drugs affecting the cytochrome P450 3A4 pathway which is the major metabolic pathway of most immunosuppressive drugs.^10,11,16,102 Further, local practice of complementary and alternative medicine use should be kept in mind as cause of DILI.¹⁰³

De-novo and Recurrent Non-alcoholic Fatty Liver Disease

Recurrent of non-alcoholic fatty liver disease (NAFLD) is almost universal post-LT and may present with mildly elevated aminotransferases in a hepatocellular pattern.^55,56 Up-to one-third may have non-alcoholic steatohepatitis with significant fibrosis in 5%–15%. De novo NAFLD^104,105 also quite common due to high prevalence of post-transplant metabolic syndrome as a result of drugs (steroids) improved appetite and rapid weight gain (sarcopenic obesity) after LT.^55,104 It may affect 20%–30% recipients although with lesser incidence of NASH and advanced fibrosis than those with recurrent NAFLD^15,55,106 (Table 2).

Recurrence of Primary Disease

Recurrence of primary disease generally occurs more than a year after LT.^11,15,53 Autoimmune liver diseases such as autoimmune hepatitis (AIH), PSC, and primary biliary cholangitis (PBC) can recur as can alcohol related liver disease (ALD) secondary to recidivism in 10–30% patients.^53,54

Recurrence of AIH, PBC, and PSC can be seen in approximately 20–30%, 20%, and 15–20% recipients at 5-years after LT.^14,53,54 AIH presents with mild-moderately raised aminotransferases in a hepatocellular pattern whereas PBC and PSC present with cholestatic LFT derangement. Clinical features and diagnostic criteria are similar to pre-LT criteria and require liver biopsy and exclusion of other possible causes.^53,107 There is limited data with respect to de novo AIH post-LT and has been described more commonly in pediatric LT recipients especially those who received grafts from females or older donors than adult LT recipients.^53,54

Extra-hepatic Causes

Many primarily extrahepatic diseases can result in deranged LFT either due to involvement of liver or as bystander hepatic injury.12, 13, 14 Fluid overload in chronic heart failure or chronic kidney disease can lead to congestive hepatitis presenting as firm hepatomegaly, dilated hepatic veins on imaging, and raised aminotransferases (AST is usually more than ALT).^10,16 Systemic sepsis can have cholestatic pattern of deranged LFT.⁹⁴ Haemolysis/hematoma resorption also have indirect hyperbilirubinemia and/or raised AST.¹⁴ Ischemic hepatitis usually presents with massively raised aminotransferases (AST is usually more than ALT). Muscle injury or myositis is another extrahepatic source of AST.^14,16 Certain tropical infections such as scrub typhus, leptospirosis, malaria, dengue, and typhoid can derange LFT and sometimes also present as acute liver failure (mimicker).^108,109 Patients with coronavirus disease may also develop elevated aminotransferase as a result of bystander injury and DILI.^108,110

Finding of deranged LFT is common at various time points after LT. They can present with myriad of clinical signs and can have variable severity. Individualized evaluation depending on severity, time since LT, pattern of LFT derangement, and other factors as outlined above is imperative to achieve early diagnosis. Quick and focused evaluation can elucidate the underlying cause in most cases with improved patient outcomes. We outline a pragmatic approach to evaluate these patients in Figure 1.

Credit authorship contribution statement

Saurabh Mishra: Literature review, writing-original draft, writing-review and editing and final approval of manuscript.

Sunil Taneja: Literature review, writing-review and editing and final approval of manuscript.

Conflicts of interest

The authors have none to declare.

Funding

None.

Disclosure statement

Nothing to disclose.

Appendix A. Supplementary data

The following is the Supplementary data to this article.