FIB4

FIB-4, or the fibrosis-4 index, is a noninvasive scoring system that estimates the degree of liver fibrosis in chronic liver disease using age and routine laboratory tests. It is intended to help identify patients who may have significant fibrosis or cirrhosis without resorting to liver biopsy.

Calculation: FIB-4 = (Age in years × AST [U/L]) / (Platelet count [10^9/L] × sqrt(ALT [U/L])).

Applications: It is commonly used in chronic hepatitis C and nonalcoholic fatty liver disease (NAFLD), as well as in HIV co-infection. It helps stratify risk for advanced fibrosis and guides decisions on further testing, such as elastography or biopsy, or timing of treatment.

Interpretation: Thresholds vary by patient population; for NAFLD common cutoffs are <1.3 to rule out significant fibrosis, >2.67 to suggest advanced fibrosis, with intermediate 1.3–2.67. For hepatitis C, thresholds like <1.45 to rule out advanced fibrosis and >3.25 to indicate advanced fibrosis have been reported. Because thresholds are context dependent, results should be interpreted with clinical data and in conjunction with imaging or histology when needed.

Limitations and caveats: FIB-4 can be influenced by age, platelet count, and transaminase elevations unrelated to fibrosis; it performs less well in acute liver injury, thrombocytopenia from other causes, or in certain populations. It is a screening tool rather than a definitive diagnosis, and indeterminate results may require further testing.

Overall, FIB-4 provides a simple, accessible estimate of fibrosis risk and can aid initial assessment and monitoring in chronic liver disease.