Key words : Hepatic fat, Liver biopsy, Transient elastography

Introduction

Living donor liver transplant (LDLT) is increasingly performed in pediatric patients and in Asian countries where the number of organs from deceased donors remains small.^1,2 Nonalcoholic fatty liver disease is an increasingly diagnosed medical problem in different populations and is the most common cause of liver cirrhosis and reason for liver transplant.^3-5 Therefore, an increased prevalence of hepatic steatosis among candidates of living related liver donation is anticipated and has been already reported.⁶

Complete clinical and laboratory evaluations of potential donor candidates are mandatory before LDLT for selection of a medically suitable donor. Estimation of liver fat among living liver donors is one of the main work-ups in the period before LDLT.⁷ Although minimal hepatic steatosis is considered to be safe and is frequently present in living liver donors, higher degrees of steatosis might have negative effects on graft survival and have been shown to be associated with primary graft dysfunction and other posttransplant complications.^8,9

To date, there is no optimal method for estimation of hepatic steatosis before LDLT, but liver biopsy has been traditionally used for this purpose. It should be noted that liver biopsy is rather an invasive method and might be accompanied with devastating complications such as bleeding, perforation of hollow viscous, biliary damage, and pneumothorax.¹⁰ Controlled attenuation parameter (CAP) during transient elastography (TE) is a new technique for noninvasive estimation of hepatic fat.11 Controlled attenuation parameter is inexpensive and can be easily and rapidly performed. This study aimed to investigate the usefulness of CAP compared with liver biopsy for pretransplant estimation of hepatic steatosis in living liver donors.

Materials and Methods

The Shiraz Liver Transplant Registry is an ongoing registration of adult and pediatric liver transplant recipients that started in April 1993 at the Namazi Hospital and the Abu-Ali Sina Hospital affiliated with Shiraz University of Medical Sciences, Shiraz, Iran. In this retrospective study of data collected between May 2015 and May 2017, we included all individuals who underwent CAP with TE and ultrasonography-guided liver bioysy as a part of donor evaluations before LDLT from first or second degree relatives (father, mother, brother, sister, uncle, or aunt). Liver biopsy specimens were reviewed for steatosis, steatohepatitis, fibrosis, and other pathologies by an expert pathologist. Clinical and laboratory data of living liver candidates were reviewed and collected.

Measurement of controlled attenuation parameter
Hepatic steatosis was noninvasively estimated by CAP using M probe during TE. These measurements were done by 1 expert within 7 days before liver biopsy, with measurement considered to be reliable if 10 valid successful acquisitions were recorded. Results of CAP measurements are expressed in decibel per meter (dB/m).

Ethics
Patients provided consent for use of their anonymized data before registration in the transplant database. This study was approved by our Institutional Review Board and conducted in accordance with the Helsinki Declaration as revised in Seoul 2008.

Statistical analyses
Continuous and categorical variables were compared using t test and chi-square test, respectively. Data are presented as means ± standard deviation for numeric variables and as percents and counts for categorical variables. A one-way analysis of variance and post hoc Tukey test were used to compare different degrees of hepatic steatosis in liver biopsies and in CAP values. Pearson correlation coefficients were used to assess correlations of metabolic indexes with CAP values after liver transplant. Linear regression analysis was used to identify continuous variables associated with CAP values. P < 0.05 was considered statistically significant. Statistical analysis was performed with SPSS version 20.0.

Results

Baseline clinical characteristics of study populationbr> Our study included 49 participants who underwent both liver biopsy and CAP measurement. Baseline characteristics of study participants are outlined in Table 1. There were 25 men (51%) and 24 women (49%). Mean age of the study participants was
30.16 ± 4.25 years. There were no donors with history of overt diabetes, hypertension, or dyslipidemia receiving medications. There were no participants with hepatitis B or hepatitis C virus seropositivity, and autoimmune markers were all negative.

Results of controlled attenuation parameter and liver biopsy
From 49 liver donor candidates, 21 participants (42.9%) had different degrees of hepatic macro­steatosis in their liver biopsies. Thirteen donor candidates (61.9%) had >10% hepatic steatosis and 8 donor candidates (38%) had ?10% of hepatic steatosis. Mild steatohepatitis was detected in liver biopsies of 8 donors (16.3%). A mild degree of hepatic fibrosis was seen in 2 donor candidates (4.1%).

In CAP measurements, 15 donor candidates (30.6%) had different grades of hepatic steatosis. Eight participants (16.3%) had grade 1 steatosis, 5 participants (10.2%) had grade 2 steatosis, and 2 participants (4.1%) had grade 3 hepatic steatosis.

Correlation between clinical and laboratory data of donor candidates and controlled attenuation parameter
Correlations between CAP values and clinical characteristics of donor candidates are summarized in Table 2. Using Pearson correlation test, we found that CAP was positively correlated with fasting blood sugar (P < .001), aspartate aminotransferase (P < .001), alanine aminotransferase (P < .001), alkaline phosphatase (P = .002), low-density lipoprotein (P < .001), cholesterol (P < .001), triglyceride (P = .005), and body mass index (BMI, calculated as weight in kilograms divided by height in meters squared) (P < .001). In linear regression analysis, BMI and serum alkaline phosphatase were independently associated with CAP values (Table 2).

Diagnostic performance of controlled attenuation parameter versus liver biopsy for diagnosis of hepatic steatosis
The association between CAP values and hepatic steatosis in liver biopsy is outlined in Figure 1. Mean CAP values were 178.14 ± 39.76 dB/m in donor candidates without hepatic steatosis in biopsy, 223.23 ± 58.86 dB/m in donor candidates with <10% hepatic steatosis in biopsy, and 249.37 ± 64.87 dB/m in donor candidates with ?10% hepatic steatosis in biopsy (F[2,47] = 8.03; P = .001).

With the use of chi-square test, of the 21 donor candidates who had hepatic steatosis in liver biopsy, 13 individuals were diagnosed to have steatosis in TE. Of the 28 donor candidates without hepatic steatosis in liver biopsy, 26 individuals had no steatosis in TE (odds ratio: 21.12; 95% CI, 3.91-114.08; P < .001).

Receiver operating characteristic curves based on different thresholds of CAP for diagnosis of steatosis and steatohepatitis in liver biopsies of donor candidates are outlined in Figure 2. The area under the curve and optimal cutoff values, positive and negative predictive values, and sensitivity and specificity levels of CAP compared with liver biopsy as standard diagnostic method of diagnosis of hepatic steatosis are outlined in Table 3.

Discussion

Results of this study showed that CAP was comparable to liver biopsy for evaluation of hepatic steatosis in donor candidates before LDLT. The CAP measurements were especially useful for exclusion of presence of hepatic steatosis in living liver donor candidates. We found that CAP could identify moderate steatosis with good sensitivity and specificity and that CAP was associated with lipid profile and independently correlated with BMI.

Hepatic steatosis in living donor candidates can have a negative impact on outcomes of LDLT. It has been reported to be associated with donor morbidity, ischemic-reperfusion injury, and biliary complications^11,12; these complications are highly associated with degree of hepatic steatosis. Although steatosis <30% might have no detrimental impact on liver regeneration and posttransplant outcomes,13 higher degrees of steatosis have been associated with substantial morbidity and complications.¹⁴

Several imaging techniques and laboratory measures have been used for noninvasive detection of hepatic steatosis in donor candidates before LDLT. In a retrospective study, magnetic resonance (MR) elastography with MR fat quantification were useful for detection of hepatic steatosis in living liver donors with 100% sensitivity.¹⁵ Magnetic resonance spectroscopy is another MR-based technique for quantification of hepatic fat content and has been reported to be useful for estimation of liver steatosis in living liver donors.¹⁶ In a meta-analysis study on the possible role of computed tomography (CT) for detection of hepatic steatosis in donor candidates, results showed that CT was not accurate for estimation of presence of hepatic steatosis but could detect significant (>10%) hepatic steatosis in liver donor candidates.¹⁷ We have previously shown that hepatic CT volumetry might be useful for detection of steatosis/steatohepatitis in potential liver donor candidates before LDLT.¹⁸ Measurement of visceral fat area during CT is another imaging technique for estimation of hepatic steatosis that has been reported to be useful as an additional tool for selection of proper living liver donors.¹⁹

Controlled attenuation parameter is a newly developed technology for quantitative estimation of hepatic fat and is based on the degree of ultrasonography attenuation by liver fat during TE.²⁰ It has been reported that CAP has high diagnostic utility for both detection and grading of hepatic steatosis and can accurately estimate even low grades of steatosis.^21-23 In patients with chronic liver diseases of various etiologies, CAP values were reported to be a strong predictor of hepatic steatosis compared with the gold standard of liver biopsy.^24-26 Although this method is being increasingly adopted and applied in different areas of hepatology, there is still no consensus on the role of CAP in liver transplant. Few studies have investigated the role of CAP for estimation hepatic steatosis in brain dead donors. In a series of 23 brain dead donors, CAP and liver stiffness measurements were good predictors of histological status and steatosis.²⁷ Another recently published study reported the usefulness of CAP for measurement of hepatic steatosis in deceased liver donors.²⁸

The practice of using noninvasive methods instead of liver biopsy for evaluation of hepatic steatosis in living liver donors is still evolving, and there is still no agreement about the usefulness of CAP. Only few studies are available in the literature focusing on this aim. In a retrospective study, Kim and colleagues reported that liver to spleen attenuation in nonenhanced CT combined with CAP measurement during TE could reliably predict hepatic steatosis in living liver donor candidates.²⁹ Another study showed that CAP was beneficial for diagnosis of steatosis (?grade 2) with sensitivity and specificity of 83.3% and 81.6%, respectively.³⁰ In a cross-sectional study, a cutoff value of 257 dB/m in CAP was a good predictor of hepatic steatosis in living liver donor candidates.³¹

Our findings are consistent with results of the few previous studies, confirming the usefulness of CAP for estimation of hepatic steatosis before LDLT. Our results could contribute to the use of CAP for noninvasive assessment of the liver allograft among healthy donor candidates before LDLT, to exclude significant hepatic steatosis and to decrease the need for invasive liver biopsy. However, further large-scale studies are needed to validate CAP for this purpose.

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