The NAFLD prevalence in diabetic patients is higher in females than in males. NAFLD group had significantly higher biochemical indexes and obesity indexes suggesting metabolic impairments than the NO-NAFLD group. Only in females, we found hepatic enzymes (ALT/AST) level is higher in NAFLD group than No-NAFLD group, while the mean level in the NAFLD group was not over upper limit of normal (ULN). This result confirmed with the study that demonstrated elevated levels of ALT/AST in 54% of NAFLD patients 19.
Our findings confirm that MetS was closely related to NAFLD, and finds a stepwise increase in the prevalence of NAFLD according to the number of components of MetS. Significant differences of the key markers of metabolic dysfunction were also found between NAFLD group and NO-NAFLD group. In the NAFLD group, there were significantly higher prevalence of MetS, lower levels of HDL and higher levels of WC and TG than in NO-NAFLD group, proving conclusion in other studies that most patients with NAFLD had same relevant MetS features 20, 21. Previous studies have reported that as a main cause of MetS, IR plays a critical role in the progress of NAFLD. IR leads to increases in insulin levels, which enhances lipid storage by promoting hepatic triglycerides synthesis and inhibiting lipolysis 22. This could explain why IR works in the association between MetS and NAFLD. Since extrahepatic complications occur across multiple organ systems, the extra-hepatic impact includes CVD, one feature of MetS, has been the main causes of death in NAFLD patients 23.
The values of the 11 obesity indices analyzed resulted higher in the NAFLD than the NO-NAFLD group as confirmed in other studies. A previous study showed good discriminatory ability of BMI, WHtR, CI, LAP, and ABSI were measured in the diagnosis of NAFLD 9, and another study reported that TyG level is an independent risk factor of NAFLD, and TyG index plays a partial mediating role in the relationship between WHtR and NAFLD24. In patients with type 2 diabetes, the non-invasive HIS score is considered as an easy, convenient and inexpensive screening for fatty liver 25. This study also demonstrated the associations among NAFLD and various obesity-related indices, which further supported for the application of these indices to predict NAFLD. The fact may be explained by the presence of obesity with IR and dyslipidemia, which can promote hepatic steatosis. Furthermore, visceral fat, subcutaneous fat as well as IR could be important in the pathogenesis of NAFLD 26–28.
For all indices, the calculated AUC showed larger areas for females than males. The largest AUC of these indices were different in different sex and age groups. The best percentage for identifying NAFLD was obtained using CI. With a view to the false negative rate (NAFLD missed %), the best performance was achieved by CUN-BAE while HIS was the worst. On the other hand, HIS is the best methods to reduce the need for US, followed by TyG and LAP. On the basis of cut-offs obtained, we compared the real performance of each formula. The results suggest that all the formulas can reduce the number of US. The best performance was obtained with HIS, TyG and LAP, and the worst performance with CUN-BAE, CI and ABSI. These findings are in accordance with the PPV of each formula considered.
Our findings recommend LAP the best formula to identify people with NAFLD combined a high PPV and NPV. It combined a good reduction in the need for US, with a small false negative rate (% NAFLD missed). A cross-sectional study of 40,459 subjects demonstrated that LAP was significantly associated with the severity of NAFLD, and that LAP had a strong diagnostic value for NAFLD 29. Another study also confirmed that LAP is a strong and easily obtainable predictive index of NAFLD for children 30. Furthermore, it is simple to apply as was calculated separately in males and females, and it requires only one anthropometric measure and one biochemical index and reflect the body content of visceral fat theoretically.
There are several shortcomings in this study. First, causality cannot be established due to the cross-sectional study design. Second, individual-level factors such as economic status, occupation, social activities were not included in our analysis, which may have some extent influence on fatty liver. Third, the study population involving only residents of southern China, further studies involving other populations are therefore warranted to add to the reliability of this finding.