With the recent conditional approval of resmetirom by the US Food and Drug Administration, the treatment of metabolic dysfunction-associated steatotic liver disease (MASLD) has potentially entered a new era, requiring a comprehensive understanding of the strengths and weaknesses of non-invasive tests (NITs) for diagnosing and monitoring MASLD-related fibrosis. This article focuses on F2/F3 liver fibrosis and summarises the current application status of NITs, including serum biomarkers, imaging methods and their combined use in the management of MASLD. The article highlights the application of NITs in several areas, including diagnosis and baseline stratification, monitoring progression of fibrosis, prediction of liver-related clinical events, as well as assessment of disease regression, remission and long-term liver-related outcomes. Furthermore, we compare the advantages and limitations of NITs and propose practical strategies for integrating them into clinical practice. Additionally, we highlight the main challenges currently faced in the application of these NITs and potential future research avenues. We suggest that future studies prioritise the validation of NITs across diverse ethnic populations. We believe it essential to explore the role of NITs in dynamic monitoring and integration of multiomics technologies, artificial intelligence and personalised risk models to improve diagnostic accuracy and treatment planning.

Background: Liver biopsy for the diagnosis of non-alcoholic steatohepatitis (NASH) is limited by its inherent invasiveness and possible sampling errors. Some studies have shown that cytokeratin-18 (CK-18) concentrations may be useful in diagnosing NASH, but results across studies have been inconsistent. We aimed to identify the utility of CK-18 M30 concentrations as an alternative to liver biopsy for non-invasive identification of NASH. Methods: Individual data were collected from 14 registry centers on patients with biopsy-proven non-alcoholic fatty liver disease (NAFLD), and in all patients, circulating CK-18 M30 levels were measured. Individuals with a NAFLD activity score (NAS) ≥5 with a score of ≥1 for each of steatosis, ballooning, and lobular inflammation were diagnosed as having definite NASH; individuals with a NAS ≤2 and no fibrosis were diagnosed as having non-alcoholic fatty liver (NAFL). Results: A total of 2571 participants were screened, and 1008 (153 with NAFL and 855 with NASH) were finally enrolled. Median CK-18 M30 levels were higher in patients with NASH than in those with NAFL (mean difference 177 U/L; standardized mean difference [SMD]: 0.87 [0.69–1.04]). There was an interaction between CK-18 M30 levels and serum alanine aminotransferase, body mass index (BMI), and hypertension (P < 0.001, P = 0.026 and P = 0.049, respectively). CK-18 M30 levels were positively associated with histological NAS in most centers. The area under the receiver operating characteristics (AUROC) for NASH was 0.750 (95% confidence intervals: 0.714–0.787), and CK-18 M30 at Youden's index maximum was 275.7 U/L. Both sensitivity (55% [52%–59%]) and positive predictive value (59%) were not ideal. Conclusion: This large multicenter registry study shows that CK-18 M30 measurement in isolation is of limited value for non-invasively diagnosing NASH.