FIB-4 / Liver Fibrosis

FIB-4 is a non-invasive fibrosis index that estimates the degree of liver fibrosis using age, AST, ALT, and platelet count. It was originally validated in HIV-HCV coinfection but is now widely used for MASLD/NAFLD screening. It correlates with the METAVIR fibrosis score: F0-F1 (no/minimal fibrosis) vs F3-F4 (advanced fibrosis/cirrhosis). It does NOT measure inflammation (steatohepatitis) or steatosis (fat content).

FIB-4 is a blood-based screening tool — best for ruling OUT fibrosis (high NPV). FibroScan (vibration-controlled transient elastography) directly measures liver stiffness and is more accurate for confirming fibrosis. The recommended pathway is: FIB-4 first → if indeterminate or high → FibroScan or ELF test → if still concerning → hepatology referral ± biopsy. FibroScan results: <8 kPa (low risk), 8-12 kPa (indeterminate), >12 kPa (advanced fibrosis likely).

In 2023, a multi-society consensus renamed NAFLD to MASLD (metabolic dysfunction-associated steatotic liver disease). MASLD requires hepatic steatosis PLUS at least one cardiometabolic risk factor (BMI >= 25, diabetes, hypertension, dyslipidemia, waist circumference criteria). NASH is now MASH (metabolic dysfunction-associated steatohepatitis). The new terminology better reflects the metabolic basis of the disease and reduces stigma associated with the term "fatty."