FIB-4 Calculator

The FIB-4 index is calculated using a specific mathematical model that weighs routine metabolic markers against patient age. The foundational equation is expressed as: FIB-4 = (Age × AST) / (Platelets × √ALT). In this calculation, age is measured in years, AST and ALT are recorded in units per liter (U/L), platelets are measured in 10^9/L (or thousands per microliter), and √ALT represents the square root of the alanine aminotransferase value. Lower scores typically suggest minimal fibrosis, while elevated indices point toward advanced scarring requiring further diagnostic evaluation like elastography or biopsy.

Consider a 50-year-old patient undergoing routine metabolic screening. Their laboratory results show an AST level of 64 U/L, an ALT level of 49 U/L, and a platelet count of 150 × 10^9/L. First, we determine the square root of the ALT value (√49 = 7). Next, we multiply the patient's age by their AST level (50 × 64 = 3,200). We then multiply the platelet count by the square root of the ALT (150 × 7 = 1,050). Finally, dividing the numerator by the denominator (3,200 / 1,050) yields a FIB-4 score of approximately 3.05, placing the patient in a higher-risk category that warrants professional hepatology consultation.

Ensure that all laboratory values used in the calculator originate from the same blood draw to maintain consistency. Always verify unit measurements, particularly for platelet counts, as reporting variations can drastically alter the final calculation. Remember that the FIB-4 score is a screening indicator rather than a definitive diagnosis and must be interpreted within the broader context of a patient's complete clinical history.