Failure of Fib-4 to Identify Advanced Liver Fibrosis in Patients With Metabolic Syndrome and Masld Without Diabetes

The fibrosis-4 index (FIB-4) is widely used to identify patients with metabolic dysfunction-associated steatotic liver disease (MASLD) who require further fibrosis assessment. However, a low result does not eliminate advanced fibrosis, including in patients with metabolic syndrome without diabetes. This narrative review critically examines diagnostic failure in this population, distinguishing biopsy-confirmed advanced fibrosis from elevated liver stiffness and separating impaired sensitivity from a high negative predictive value. Targeted PubMed searches and professional guidance were reviewed through November 9, 2026. Evidence was synthesized descriptively, without a new meta-analysis. In a biopsy-referenced fatty liver cohort, FIB-4 at a threshold of 1.3 had 84% sensitivity among participants without diabetes, demonstrating residual false negatives despite better discrimination than in those with diabetes. In a separate cohort without diabetes, sensitivity was 69.6% against a transient-elastography endpoint of at least 8 kPa; this threshold should not be equated with histological F3–F4 disease. Age dependence, preserved platelet counts, aminotransferase patterns, heterogeneous metabolic phenotypes, and differences in reference standards complicate interpretation. Contemporary multinational studies support moderate FIB-4 discrimination and more consistent performance of imaging-based or composite tests across several subgroups. Evidence specifically restricted to metabolic syndrome, MASLD, and absence of diabetes remains limited. Furthermore, a recent study in this exact metabolic population evaluated associations with fibrosis surrogates rather than independently establishing FIB-4 sensitivity. FIB-4 remains useful as an accessible first assessment, but low values should be interpreted within the patient's clinical risk. Persistent suspicion, young age with substantial metabolic burden, or discordant findings justify additional assessment rather than categorical reassurance.