Non-alcoholic fatty liver disease (NAFLD) is reaching epidemic proportions worldwide in parallel with the increasing prevalence of obesity over the past three decades . It has been associated with several risk factors, particularly IR, type II DM, hyperlipidemia, and obesity that are the main features of metabolic syndrome .
Routine liver biopsy in such highly prevalent disease seems impractical because of its invasiveness, especially in the presence of imaging techniques with more availability and safety as ultrasound. Unfortunately, ultrasound has limited sensitivity when steatosis is less than 30% on liver biopsy .
Despite its accuracy in quantifying liver fat, especially its advanced techniques like MRI-estimated proton density fat fraction (MRI-PDFF) , MRI is still time-consuming, relatively expensive, and often unavailable on wide-scale; therefore, there is an urgent need to develop and validate a simple, reproducible, noninvasive method that accurately identifies NAFLD patients with the highest risk of disease progression, meanwhile, allowing frequent monitoring of the disease and response to therapy .
Thus, our aim in the current study was to evaluate the clinical value of NAFLD-LFS and CIMT in the prediction of NAFLD in parallel with atherosclerotic cardiovascular disease.
Many serum markers have shown acceptable diagnostic accuracy as defined by an AUROC > 0.8 . NAFLD fibrosis score (NFS) and fibrosis 4 calculator (FIB-4) have been externally validated in ethnically different NAFLD populations, with consistent results. NFS, FIB-4, enhanced liver fibrosis (ELF), and FibroTest predict overall mortality, cardiovascular mortality, and liver-related mortality. Moreover, NFS can predict incident diabetes, and changes in NFS are associated with mortality. The tests perform best at distinguishing advanced (≥ F3) versus non-advanced fibrosis but not significant fibrosis (≥ F2) or any fibrosis (≥ F1) versus no fibrosis. Importantly, the NPV for excluding advanced fibrosis is higher than the corresponding PPV ; therefore, noninvasive tests may be confidently used for first-line risk stratification to exclude severe disease. However, predictive values depend on prevalence rates, and most of these studies have been conducted in tertiary centers where the pre-test probability of advanced fibrosis is higher than in the community.
The prevalence and incidence of CVD is higher in NAFLD than in matched controls and linked to the association between NAFLD and MS components . CVD is a main common cause of mortality rather than liver disease itself in NAFLD. In most anecdotal studies, atherosclerotic markers (low HDL, high TG) or inflammatory markers (high sensitive C-reactive protein) and increased levels of procoagulant/prothrombotic factors are more commonly encountered in NAFLD patients than in persons without steatosis. Besides, pre-atherogenic lesions like increased CIMT; coronary artery, abdominal aortic, and aortic valve calcifications; and endothelial dysfunction are also more prevalent in NAFLD patients and, in some studies, correlated with the histological severity .
Our study revealed that NAFLD-LFS showed a high diagnostic performance in discriminating patients with NAFLD from healthy controls, with an AUROC for NAFLD-LFS as a predictor of hepatic steatosis of 0.991. At a value of − 1.628 as a possible cutoff value to discriminate NAFLD, it showed a sensitivity of 96.7%, specificity 100%, PPV 100%, NPV 93.8%, and diagnostic accuracy 97.8%, a result that is in concordance with Cheung et al.  who found that NAFLD-LFS is the best prediction score for ultrasound-proved NAFLD, and can predict mortality, including cardiovascular and liver-related mortality with an AUROC of 0.771 and a high specificity (96.4%).
Interestingly, NAFLD-LFS was first developed from a cohort study including 470 well-characterized Finnish individuals, in whom liver fat content was measured using proton magnetic resonance spectroscopy, and it was reported that MS, type II DM, and serum insulin, AST, and ALT concentrations allowed prediction of NAFLD. The score had an AUROC of 0.87 in the estimation and 0.86 in the validation group, and a cutoff point at − 0.640 predicted increased liver fat content with an average sensitivity and specificity (86% and 71%, respectively) .
Furthermore, our study revealed higher NAFLD-LFS levels among NAFLD cases than in healthy controls (median − 0.94 vs. − 2.02; p < 0.01). This result was close to that of a retrospective analysis on 324 consecutive liver biopsies performed between 2000 and 2010 for suspicion of NAFLD, where five steatosis biomarkers were calculated including NAFLD-LFS using data retrieved at the time of each liver biopsy, where NAFLD-LFS had higher mean values in grades of mild steatosis than no steatosis, and in moderate than mild steatosis (p = 0.001) .
Several studies have proven the strong possibility of a carotid plaque in patients with hepatic steatosis ; thus, we measured the CIMT in both NAFLD patients and healthy controls to evaluate its clinical value in prediction of NAFLD. Our study revealed that the mean average CIMT among NAFLD cases was significantly higher (0.74 ± 0.14 cm) than that of healthy controls (0.65 ± 0.11 cm) (p = 0.025). Our findings were supported by Fracanzani et al.  who evaluated CIMT values in 125 patients with NAFLD and 250 healthy individuals; they found that the mean CIMT was significantly higher in NAFLD patients. Also, our results are comparable with the results of Nahandi et al.  who evaluated CIMT values in 49 diabetic NAFLD patients, 50 non-diabetic NAFLD patients, and 52 normal controls, and they reported that there is a significant association between the presence of NAFLD and atherosclerosis determined by CIMT. Gastaldelli and colleagues  proved the independent association between FLI and IMT on subjects without diabetes or hypertension in a population-based study including 1307 patients.
Also, we found that the mean average CIMT of NAFLD cases with MS was significantly higher (0.9 ± 0.1 cm) than that of NAFLD cases without MS (0.67 ± 0.9 cm) (p < 0.01), and this is in agreement with Koskinen et al. , who reported a higher incidence of NAFLD and atherosclerosis among patients with MS. In the contrary, a population-based study in south Iran, on 290 NAFLD cases compared to 290 healthy controls, suggested that NAFLD could be a risk factor for carotid atherosclerosis, independently of its association with the MS .
Furthermore, by multiple regressions analysis, using the stepwise method, HOMA-IR, total bilirubin, INR, and CIMT were together the most sensitive independent variables that predicted the dependent variable NAFLD-LFS.