FIB-4 Index Calculator

How it is calculated

The score is FIB-4 = (age × AST) / (platelets × √ALT). Age is in years, AST and ALT in U/L, and platelets in ×10⁹/L, the unit most lab reports use (typical counts are in the low hundreds). The tool rejects a platelet count above 2000, so a per-microlitre value such as 200000 returns no result; enter 200 instead. All four values must be above zero and age must be 130 or below. The result is rounded to two decimals and sorted into three bands using fixed cut-offs: below 1.45 is low risk, above 3.25 is high risk, and 1.45 to 3.25 inclusive is indeterminate. The same cut-offs are applied at every age. It is a screening estimate, not a diagnosis.

Common mistakes

• Entering platelets per microlitre (for example 200000) instead of ×10⁹/L (200). The tool refuses values above 2000, and a value off by 1000 would change the score a thousand-fold.
• Swapping AST and ALT. Only ALT sits under the square root and in the denominator, so reversing them gives a different score and can move the result into the wrong band.
• Treating a low-risk band as a clean bill of health. The index only screens for advanced fibrosis and does not rule out other liver conditions.
• Using values from different blood draws or labs with different units. AST and ALT must be in U/L; a result reported in another unit has to be converted first.
• Reading an indeterminate score (1.45 to 3.25) as a mild result. It means the score is inconclusive and usually calls for further assessment by a clinician.