In this cross-sectional observational study, we aimed to evaluate the role of some non-invasive, simple, readily available, and cheap indices, namely, FIB-4, APRI, and NFS in the detection of significant fibrosis (≥ F2) in patients with NAFLD, as well as their role in detecting any stage of fibrosis in a subgroup of patients with simple steatosis. Similarly, we could evaluate the predictability of other non-invasive steatosis indices (HSI and FLI) and compare them to US findings (grading of liver brightness and subcutaneous and visceral fat measurements) taking liver biopsy results as a standard in diagnosis and grading of hepatic steatosis/fibrosis.
Significant fibrosis (≥ F2) was observed in 20.6%, while advanced fibrosis (F3-4) was seen in 3.1% of patients. According to the National Health and Nutrition Examination Survey conducted in 1988-1994, advanced fibrosis (NFS > 0.676) was only observed in 3.2% of patients with NAFLD [17].
In this study, the prevalence of T2DM was significantly higher in the NASH group compared to the simple steatosis one. It is well known that diabetes risk and type 2 DM (T2DM) are closely associated with the severity of NAFLD, progression to NASH, advanced fibrosis, and HCC development [18].
Regression analysis for predictors of significant fibrosis revealed that lower serum albumin, higher bilirubin, and NFS were significantly associated with higher grades of fibrosis (≥ F1). Several studies revealed that NFS is an important predictor of advanced fibrosis in NAFLD patients [19].
Although patients with simple steatosis without inflammation were considered for a long time to have a benign course with little progression [1], this view has been modified by results of different studies demonstrating that steatosis alone may progress to NASH with fibrosis, however, at a slower rate [20].
In the subgroup of patients with simple steatosis, predictors of fibrosis were older age, lower serum albumin, FIB4, and NFS. The importance of identifying patients who had fibrosis is that this could carry the risk of progressing to NASH. In one study by Pais et al., 64% of 25 patients with simple steatosis developed NASH after an average of 3.7 years. They showed that severe ballooning, presence of bridging fibrosis, older age, and deterioration of metabolic risk factors were associated with a more rapid progression [21].
In the current study, FIB4, APRI, and NFS had comparable AUC for detecting the presence of any grade of fibrosis. Detecting the early stages of fibrosis is of great importance in preventing disease progression to minimize complications [22]. On the other hand, all markers were poor predictors of significant fibrosis ≥ F2. Contrarily, Castera in 2018 reported AUC for transient elastography, FIB-4, and the NAFLD fibrosis scores in diagnosing severe fibrosis-cirrhosis of 0.88, 0.84, and 0.84 respectively [23]. Mohamed et al. studied the diagnostic performance of FIB4, NFS, and APRI in NAFLD. They found AUC for advanced fibrosis of 0.936, 0.916, and 0.907 [24]. Also, in a meta-analysis of 13 studies consisting of 3064 patients, NFS had an AUROC of 0.85 for predicting advanced fibrosis [25]. This difference may be related to the small number of patients with advanced fibrosis (≥ F3) in our study (3%).On the other hand, Nones et al. evaluated results of FIB4, APRI, and NFS in 67 patients with NAFLD, the best diagnostic accuracy was achieved with FIB 4 model (AUROC = 0.83) versus APRI and NFS. Again, the difference may be attributed to the higher number of patients with advanced fibrosis (≥ F3) in his study 18 (26.86%) compared to the current one (3%) [26].
Among non-invasive scores of hepatic steatosis, the hepatic steatosis index (HSI) has been derived from data of a Korean cross-sectional study that involved more than 10,000 patients and has been validated against ultrasound [13]. It is a promising score that seems to predict incident metabolic syndrome [27]. In the current study, HSI has been validated against liver biopsy results and showed acceptable AUC in the prediction of moderate and marked steatosis. Our results go hand in hand with those of Fedchuk et al., where HSI had an AUC of 0.65 in the prediction of the presence of hepatic steatosis [9].
The fatty liver index (FLI) was mentioned as one of the best-validated steatosis scores, as it has been externally validated in the general population or grade 3 obese persons and can variably predict metabolic, hepatic, and cardiovascular outcomes/mortality [4]. However, in the current study, FLI had unsatisfactory AUC for predicting the presence of moderate and marked steatosis and was inferior to HSI. The discrepancy maybe since the fatty liver index (FLI) has only been validated against liver ultrasonography in published studies [28] rather than liver biopsy that has been taken in our study.
Despite its limitations, ultrasound is still recommended by EASL 2016 guidelines to be the preferred first-line diagnostic procedure for imaging of NAFLD, as it provides additional diagnostic hepatobiliary information [4]. In the current study, subcutaneous adipose tissue (SAT) showed better AUC than visceral adipose tissue (VAT) in predicting moderate steatosis and similar AUC in predicting marked hepatic steatosis. Lower AUC for detection of marked steatosis in the current study may be due to the technical limitation of higher waist circumference and obesity of this cohort.
In the current study, subcutaneous adipose tissue (SAT) showed the best results among all tested non-invasive measures, namely, serum biomarkers (HSI and FLI) as well as visceral adipose tissue (VAT) by ultrasound in detecting moderate steatosis.
The main point of strength of the current study is the presence of liver biopsy results as a gold standard for comparison with non-invasive markers. Note that many other published studies lack the results of liver biopsy and compare the accuracy of non-invasive biochemical markers with imaging or controlled attenuation parameter (CAP) measures which are still not considered the gold standard for fibrosis/steatosis diagnosis. The main limitation of our study is that the main cohort of patients has no or mild degree fibrosis (F0-F1) by liver biopsy (79%), while significant and advanced fibrosis was present in 21% which may have affected the results.