FIB-4 Index (Liver Fibrosis Score)
FIB-4 is a four-number blood calculation that estimates liver scarring and is now the recommended first-line test for people with fatty liver or metabolic risk.
Plain English
Patient-Friendly Explanation
Fatty liver is common in people carrying excess weight, and the important question is not how much fat there is but whether the liver has started to scar, because scarring is what leads to cirrhosis. A liver biopsy answers that question but is invasive. FIB-4 is the alternative most clinics now use first. It is calculated from four results that are already on your report: your age, the liver enzyme AST, the liver enzyme ALT and your platelet count. Nothing extra is needed and you do not have to fast. The arithmetic is simple enough for a calculator: multiply your age by the AST level, then divide by the platelet count multiplied by the square root of the ALT level. A result below 1.3 makes advanced scarring unlikely and usually means monitoring rather than investigation. A result above 2.67 makes scarring likely enough to warrant referral to a liver specialist. The middle zone means more information is needed, usually from a liver stiffness scan, which uses a painless probe on the chest wall. Because the score includes age, a higher cut-off above 2.0 is used for people over 65, and the score is unreliable under the age of 35. In someone with a large waist, high triglycerides, high blood pressure or diabetes, FIB-4 is a cheap way of separating the many people who only need reassurance and periodic repeat testing from the minority who need proper liver assessment. It is a screening tool, not a diagnosis, and it works best repeated over time.
Medical
Clinical Definition
The fibrosis-4 index is calculated as age in years multiplied by AST in U/L, divided by platelet count in 10 to the 9 per litre multiplied by the square root of ALT in U/L. It was derived to identify advanced fibrosis in chronic hepatitis C but is now the recommended first-line non-invasive test for hepatic fibrosis in metabolic dysfunction-associated steatotic liver disease. Current practice guidance advises using FIB-4 to risk-stratify all patients with steatotic liver disease: a value below 1.3 has a high negative predictive value and can be followed in primary care, with reassessment every 2 to 3 years in lower-risk patients and every 1 to 2 years in those with prediabetes, type 2 diabetes or two or more metabolic risk factors; a value of 1.3 or above should trigger secondary assessment by vibration-controlled transient elastography or the Enhanced Liver Fibrosis test, or referral if the setting is not gastroenterology or hepatology; and a value above 2.67, or aminotransferases persistently raised beyond six months, warrants direct referral to hepatology because of the increased risk of clinically significant fibrosis. Age-specific adjustment matters: a threshold above 2.0 is used in patients over 65 years because the age term inflates the score, accuracy is low below age 35, and the index should not be applied in acutely ill patients. Diagnostic performance is good but imperfect: a biopsy-referenced series reported an area under the receiver-operating characteristic curve of 0.895 with 95.2 per cent sensitivity at a cut-off of 1.30 and 85 per cent specificity at 2.67, and sequential strategies using elastography after an indeterminate FIB-4 improve specificity and reduce unnecessary referral. FIB-4 has also been shown to predict all-cause mortality in cohorts with heart failure and to outperform the NAFLD fibrosis score for advanced fibrosis in patients with diabetes. It is affected by any condition that alters platelets or transaminases, a normal value does not exclude significant fibrosis, and it is therefore best used as a serial triage tool within a pathway rather than as a stand-alone diagnosis.
Key Insight
Why It Matters
FIB-4 turns four numbers you already have, age, AST, ALT and platelets, into a triage decision about who needs a liver stiffness scan, which is the difference between monitoring fatty liver and missing cirrhosis.
Sources
Reviewed against standard medical references.
Medically reviewed by
Family Physician & Registered Acupuncturist, Accord Medical Clinic. MBBS (NUS), Graduate Diploma in Family Medicine (NUS), Graduate Diploma in Acupuncture (Singapore College of TCM).
Last reviewed: September 2026
This page is general health education, not medical advice. Whether any treatment is appropriate for you is a decision made in consultation after assessment.
