Assessment of transient elastography in diagnosing MAFLD and the early effects of sleeve gastrectomy on MAFLD among the Chinese population
Authors: Hu Ruixiang , Wu Bing , Wang Cunchuan , Wu Zilong , Zhang Xu , Chen Xinxin , Lu Guanhua , Yuan Kaisheng 
Published: January 2024

Background:
Metabolic dysfunction-associated fatty liver disease (MAFLD) has become a prevalent chronic liver disease among patients with obesity. Bariatric surgery, such as sleeve gastrectomy (SG), shows promise in improving the unfavorable condition of MAFLD. Transient elastography (TE) can be utilized to assess the extent of steatosis and liver fibrosis, providing a noninvasive method for preoperative prediction and postoperative evaluation of MAFLD. This study aims to investigate the effectiveness of TE in diagnosing MAFLD by evaluating liver steatosis and tissue stiffness, as well as assessing the early impact of SG in the treatment of obesity-associated MAFLD.

Methods:
In this study, the authors collected preoperative and 6-month postoperative data from patients with obesity who were diagnosed with MAFLD by intraoperative liver biopsy. The patients underwent SG at our hospital between August 2021 and April 2023. The authors estimated the diagnostic accuracy for the steatosis and fibrosis categories using the area under the receiver operating characteristic curve (AUROC). The authors also evaluated the influence of disease prevalence on the positive predictive value and negative predictive value. MAFLD diagnosis was based on the liver steatosis activity and fibrosis scoring system. The authors used univariate and multivariate logistic regression analyses to identify factors contributing to severe MAFLD. To visualize the results, the authors created a nomogram and enhanced it with bootstrap resampling for internal validation. Additionally, the authors plotted receiver operating characteristic and calibration curves. The authors compared preoperative and postoperative data, including general information, laboratory tests, and TE results, to assess the early impact of SG in the treatment of obesity-associated MAFLD.

Results:
Based on the results of liver biopsy, the AUROC for controlled attenuation parameter (CAP) in identifying steatosis was found to be 0.843 (95% CI: 0.729–0.957) for S≥S1, 0.863 (95% CI: 0.786–0.940) for S≥S2, and 0.872 (95% CI: 0.810–0.934) for S=S3. The Youden limits for S≥S1, S≥S2, and S≥S3 were determined to be 271 dB/m, 292 dB/m, and 301 dB/m, respectively. Similarly, the AUROC for liver stiffness measurement (LSM)/E in detecting liver fibrosis was 0.927 (95% CI: 0.869–0.984) for F≥F2, 0.919 (95% CI: 0.824–0.979) for F≥F3, and 0.949 (95% CI: 0.861–0.982) for F=F4, with Youden cutoff values of 7.5 kPa, 8.3 kPa, and 10.4 kPa, respectively. Patients with A≥3 and/or F≥3 were classified as having severe MAFLD. Multivariate logistic regression analysis identified CAP, E, LDL, and AST as the best diagnostic factors for severe MAFLD, and a nomogram was constructed based on these factors. The AUROC of the nomogram for the assessment of severe MAFLD was 0.824 (95% CI: 0.761–0.887), which was further validated by 1000 bootstrap resamplings with a bootstrap model area under curve of 0.823. Finally, after a 6-month follow-up period, the steatosis grade and fibrosis stage of the patients were graded based on the optimal cutoff values for CAP and LSM. Significant reductions in BMI, waist circumference, HbA1c, fasting glycemia, triglycerides, high density lipoprotein (HDL), glutamic pyruvic transaminase (ALT), glutamic oxaloacetic transaminase (AST), gamma glutamyl transpeptidase (GGT), CAP, LSM, steatosis grade, and fibrosis stage were observed compared to the preoperative values.

Conclusion:
In this prospective study, the authors investigated the use of CAP and LSM as alternatives to liver biopsy for evaluating hepatic steatosis and fibrosis in patients with obesity combined with MAFLD. Furthermore, the authors examined the impact of SG on metabolic indicators and the progression of fatty liver disease during the early postoperative period, and observed significant improvements in both aspects.