Introduction
Of approximately 2 billion people who have been infected with hepatitis B virus (HBV) worldwide, more than 248 million (5–7% of the world’s population) suffer from chronic HBV infection (CHB) and about 1 million of these die per year.1 India has over 40 million HBV carriers, accounting for 10-15% of the total HBV carriers in the world.2
HBV has a complex natural history, and the interaction between viral proteins and the immune system leads to a cycle of hepatocyte damage and tissue repair.3 This repair leads to progressive liver fibrosis over time, which can be rapid, slow, or sporadic depending on disease state and the degree of active liver inflammation and injury. The assessment of liver fibrosis is vital to disease prognostication and to determining the need for treatment as well as the response to therapy. Studies in Asia and the USA have revealed that 20% to 30% of HBV carriers with persistently normal alanine aminotransferase (ALT) levels and HBV DNA levels >10000 copies/mL have grade ≥2 inflammation and stage ≥2 fibrosis on liver biopsy.4,5 A fair proportion of patients with CHB infection with normal ALT have HBV DNA ≥5 log copies/mL and significant histologic fibrosis.5 At present, the gold standard for assessment of liver fibrosis is liver histology using the Ishak6 or METAVIR7 systems. However, liver biopsy is prone to sampling error and substantial intra- and inter-observer variability, leading to over- or under-staging of fibrosis;8 in addition, the procedure also has significant morbidity, including infections, major bleeding, and ascites leakage, and can lead to mortality.9 Consequently, there is a need for non-invasive methods to accurately diagnose the presence of liver fibrosis and cirrhosis, especially while making a decision to start antiviral therapy.
Transient elastography (TE) has been shown to be an excellent non-invasive modality for assessment of fibrosis;10,11 however, it has limited availability, especially in resource-poor countries. So various non-invasive blood parameters need evaluation to find the most useful parameter for ruling out significant fibrosis.
A number of non-invasive models containing serum markers, such as serum aspartate aminotransferase (AST) to platelet ratio index (APRI),12–14 Fibrosis 4 score (FIB-4),15 gamma-glutamyl transferase (GGT)-to-platelet ratio (GPR),16 and GGT-to-albumin ratio (GAR)17 have been described in the literature. Among these markers, the FIB-4 and APRI12,18 are widely used to assess patients with chronic hepatitis but their value for assessing patients who are chronically infected with HBV remains controversial.19–22 Recently, GPR showed better performance than FIB-4 and APRI in detecting liver fibrosis in CHB West African patients; however, this was not true for French populations.23
There has been no published data from India evaluating the performance of these non-invasive blood parameters for ruling out significant fibrosis in patients with CHB. The aim of the present study was to evaluate and find out the most useful non-invasive blood parameter for ruling out significant fibrosis in CHB and to compare it with TE.
Discussion
In this study, we compared the diagnostic value of non-invasive blood parameters (APRI, FIB-4, GPR, and GAR) for assessing liver fibrosis in a patients with CHB and found that these blood parameters have NPVs above 93% and are excellent parameters for ruling-out significant fibrosis. These data indicate that these parameters can be used at bedside in place of TE, especially if the latter is not available.
Assessment of significant fibrosis is an important step for decision-making of antiviral treatment in chronically HBV-infected patients.24 The Indian National Asssociation for the Study of the Liver (INASL) guidelines recommend that in patients with hepatitis B e antigen-negative states, if ALT is <80 U/L (i.e. <2×upper limit of normal), HBV DNA is 2,000-20,000 IU/mL, and if non-invasive or invasive assessment of liver fibrosis does not show significant fibrosis, antiviral treatment need not be started and these patients may be kept under observation.2 Similarly, in patients with hepatitis B e antigen-positive state, if ALT is 40-80 U/L, HBV DNA is >20,000 IU/mL, and if non-invasive or invasive assessment of liver fibrosis does not show significant fibrosis, antiviral treatment need not be started as these patients are considered to be in the immune-tolerant phase.2
In the past (over one decade), TE has gained importance as one of the best non-invasive tests to assess liver fibrosis. In our study, TE had the best area under the receiver operating characteristic curve (0.793) compared to the blood parameters. In addition, our cut-off of 5.35 kPa for TE for significant fibrosis was similar to that in a previous French study on 1307 patients which gave a cut-off of 5.2 kPa25 and another study from India which gave a cut-off of 6 kPa.26 We found TE to have the best NPV of 100% when using this cut-off. However, TE has many disadvantages. It is not universally available, especially in resource-poor settings; its applicability is approximately 80%, which is lower than that of serum biomarkers, especially when used in the presence of ascites, obesity, and limited operator experience. It can also lead to false positive values in the case of acute hepatitis, extra-hepatic cholestasis and liver congestion. Finally, it is unable to discriminate between intermediate stages of fibrosis, it requires a dedicated device, and it does not allow for a region of interest to be chosen.27 In contrast, non-invasive serum biomarkers have many advantages: They do not require extra cost and are widely available, can be assessed both in in-patient and out-patient settings, have good reproducibility and high applicability, and most are well validated.27 However, with the multitude of blood parameters, with varying sensitivities and specificities, the best parameter for detection of or for ruling-out significant fibrosis needed evaluation. Hence, in this study, we included commonly used parameters which are available even in most resource-poor settings.
We found that the NPVs of all non-invasive blood parameters were nearly similar and ≥93%. So, all these parameters were found to have similar and excellent performance in ruling-out significant fibrosis in CHB patients (in comparison to liver biopsy). The best cut-off values of GPR, APRI, FIB-4 and GAR, especially for ruling-out of significant fibrosis, were 0.935, 2.324, 0.444 and 17.848. However, the ruling-in performance of these parameters was low, with PPVs of GPR, APRI, FIB-4 and GAR at 28%, 33%, 37% and 35% respectively. GPR was found to have slight superiority because of the highest NPV of 95%, while the NPVs of APRI, FIB-4 and GAR were 93%, 93% and 92% respectively.
APRI is the oldest and probably the most widely used non-invasive parameter to assess liver fibrosis,12,22,28 and even portal hypertension.13,14 In our study, we found the area under the receiver operating characteristic curve of APRI for significant fibrosis was 0.723, and 0.935 was the best cut-off. Our results are similar to a meta-analysis of 17 studies29 (n=3,573) that assessed APRI, and found the area under the summary receiver operating characteristic curve to be 0.77, which is almost similar to the area under the receiver operating characteristic curve in our study of 0.723. Another meta-analysis of five studies found that a cut-off of 0.5 for APRI gave a specificity of 41%, while a cut-off of 1.5 of APRI gave a specificity of 84% for detection of significant fibrosis.28
After APRI, the next non-invasive parameter which became popular was FIB-4.15 In a meta-analysis29 of 10 studies assessing the FIB-4 for the prediction of significant fibrosis (n=1,996), the area under the summary receiver operating characteristic curve was 0.75, which is similar to the area under the receiver operating characteristic curve of 0.764 in our study.
APRI and FIB-4 have been compared in many previous studies and meta-analyses and FIB-4 was found to be slightly superior. In a study Lin et al.,30 FIB-4 and APRI were compared to evaluate their diagnostic values in identifying significant fibrosis and cirrhosis among 631 CHB patients. FIB-4 had a significantly higher area under the receiver operating characteristic curve than APRI to identify significant fibrosis and cirrhosis. Using FIB-4 outside the 0.87-3.40 range, significant fibrosis could be excluded in 69.2% of patients and cirrhosis could be diagnosed in 84.4%.30 Another meta-analysis of 39 studies found that the mean area under the summary receiver operating characteristic curve value of FIB-4 was higher than that of APRI (0.76 vs. 0.72) for predicting significant fibrosis.21 Similar results were shown by Houot et al.31 in their meta-analysis, where FIB-4 had better performance than APRI. A recent large study of almost 4000 patients (the SONIC-B study aimed at ruling-out cirrhosis) also found FIB-4 performing better than APRI.22 In contrast to these studies, a small Indian study found APRI to be superior to FIB-4 and Forn’s index. The study found NPV of APRI to be 95% for excluding significant liver fibrosis, while FIB-4 with a PPV of 61% showed fair correlation with significant fibrosis.32 Moreover, the World Health Organization recommend the use of APRI for estimating liver fibrosis in patients with CHB, where limited availability of resources was an issue.24
The next non-invasive parameter was GPR, which was developed in France and Western Africa to evaluate fibrosis in subjects with HBV, particularly in low-resource settings. The investigators had compared GPR with APRI and FIB-4 and found that the area under the receiver operating characteristic curve value of GPR was significantly superior to APRI and FIB-4 at identifying ≥F2 and ≥F3 in the African training and validation cohorts.23 Another comparative evaluation of GPR versus APRI and FIB-4 in predicting different levels of liver fibrosis of CHB also found that GPR had the best performance among the three. Using a cut-off of GPR >0.50 as standard, the sensitivities and specificities of GPR in predicting significant fibrosis in hepatitis B e antigen-positive patients were 59.6% and 81.2%, and those of hepatitis B e antigen-negative patients were 60.3% and 78.3% respectively. The authors suggested that this cut-off is almost similar to our cut-off of 0.444 for ruling-out significant fibrosis.33
The most recent of the non-invasive blood parameters assessed in our study was GAR, which was developed by Li et al.17 in 2017. The investigators had compared GAR to APRI and FIB-4 and had found GAR to have the highest area under the receiver operating characteristic curve for ≥F2, ≥F3, and ≥F4 fibrosis. The area under the receiver operating characteristic curve for GAR in our study was 0.734.
There are several limitations to our study. First, the performance of these non-invasive methods was assessed in a low fibrosis setting (13%), which is assumed to be reflective of the HBV population in India. Performance in higher fibrosis settings could be different from our results. Second, our results may not apply to patients in the immune-tolerant phase. Since this was a retrospective study conducted on patients who had undergone pre-treatment liver biopsy most patients in the immune-tolerant phase, who do not merit treatment, were excluded. Third, many confounding variables, such as coexisting obesity, metabolic syndrome and metabolic associated fatty liver disease, could have influenced the results. Fourth, GPR and GAR, both of which use GGT, can be affected by biliary tract disease and by some types of drugs, and this had not been evaluated in the reported studies. As such, our results of GPR and GAR need further evaluation in prospective studies.
In conclusion, we found that non-invasive blood parameters such as GPR, APRI, FIB-4 and GAR could be a useful parameters for screening of CHB patients who are at risk for developing liver fibrosis, especially in resource-poor settings and when TE is not available. Despite significant advances in developing non-invasive biomarkers that will help in evaluating hepatic fibrosis in patients with CHB, further large, prospective studies remain essential to validate accuracy, particularly for patients with mild hepatic fibrosis.34 In addition, a combination of these non-invasive biomarkers with or without TE may help to establish an algorithm to increase diagnostic accuracy of non-invasive assessment of liver fibrosis.