FIB-4 Calculator (Liver Fibrosis)

FIB-4 in brief

The FIB-4 index (Fibrosis-4) is a simple score that estimates the likelihood of advanced liver scarring (fibrosis) from four routine values: age, AST, ALT and platelet count. It is recommended by major liver societies as the first test for assessing fibrosis in people with fatty liver disease, now called metabolic dysfunction-associated steatotic liver disease (MASLD), and is also used in viral hepatitis.

FIB-4 = (age × AST) ÷ (platelets × √ALT)

Age is in years, AST and ALT in units per litre (U/L), and platelets in 10⁹/L (for example, a platelet count of 250,000/µL is entered as 250).

Standard interpretation for adults aged 35–64:

• below 1.30 – low risk of advanced fibrosis; advanced fibrosis is unlikely
• 1.30–2.67 – indeterminate; a second test, such as elastography (FibroScan) or the ELF blood test, is recommended
• above 2.67 – high risk; referral to a liver specialist is usually recommended

From age 65, a lower cut-off of 2.0 is used instead of 1.30, because FIB-4 rises with age and would otherwise label too many older people as indeterminate. The score is less accurate in people under 35.

Worked examples

Step by step

For the first example: age 50 × AST 30 = 1,500. The square root of ALT 40 is 6.32. Platelets 250 × 6.32 = 1,581. Then 1,500 ÷ 1,581 = 0.95.

Why these four values?

• Age – fibrosis accumulates over time, so older people are more likely to have advanced scarring.
• AST – rises relative to ALT as liver fibrosis advances, partly because of reduced clearance of AST by the scarred liver.
• ALT – used in the denominator as its square root, so the score reflects the AST:ALT balance rather than the absolute level of liver inflammation.
• Platelets – fall in advanced fibrosis and cirrhosis because of increased pressure in the portal vein (portal hypertension), which enlarges the spleen and traps platelets, and because the liver makes less thrombopoietin.

Where FIB-4 comes from

FIB-4 was developed by Sterling and colleagues in 2006 in people with HIV and hepatitis C co-infection, using liver biopsy as the reference standard. The name refers to the four variables and its purpose of predicting fibrosis. It was later validated in hepatitis C alone, hepatitis B and, most importantly, in non-alcoholic fatty liver disease, where Shah and colleagues established the widely used 1.30 and 2.67 cut-offs in 2009.

FIB-4 became popular because it uses tests that almost everyone with a routine blood panel already has, costs nothing extra, and has a high negative predictive value: a low score reliably rules out advanced fibrosis in most populations. It is less good at ruling fibrosis in, which is why an intermediate or high score leads to further testing rather than a diagnosis.

Understanding liver fibrosis

When the liver is repeatedly injured – by fat accumulation and inflammation, alcohol, viral hepatitis or other causes – it heals by laying down scar tissue. Fibrosis is staged from F0 (none) to F4 (cirrhosis):

Fibrosis stage is the strongest predictor of liver-related outcomes in fatty liver disease, including cirrhosis, liver cancer and liver-related death. Early stages can improve if the cause is removed, which is why identifying people at risk matters.

From NAFLD to MASLD: a change in names

In 2023, international liver societies agreed new terminology. Non-alcoholic fatty liver disease (NAFLD) became metabolic dysfunction-associated steatotic liver disease (MASLD), and non-alcoholic steatohepatitis (NASH) became metabolic dysfunction-associated steatohepatitis (MASH). The new names describe the condition by its cause – metabolic risk factors such as excess weight, diabetes, high blood pressure and abnormal lipids – rather than by the absence of alcohol, and they avoid potentially stigmatising language. People who have metabolic risk factors and also drink moderately more alcohol fall into a new category, MetALD. Research shows that almost everyone previously classed as NAFLD meets the MASLD definition, so studies of FIB-4 in NAFLD still apply.

FIB-4 and fatty liver disease (MASLD)

MASLD affects roughly a third of adults worldwide and is closely linked to excess weight, type 2 diabetes, high blood pressure and abnormal lipids. Most people with MASLD do not develop serious liver disease, but a minority progress to advanced fibrosis and cirrhosis. The challenge is to find that minority without sending everyone for specialist tests.

Current guidelines recommend a two-step pathway:

1. Step 1: FIB-4 in people with MASLD or with risk factors such as type 2 diabetes, obesity with metabolic complications, or persistently raised liver enzymes.
2. Step 2: if FIB-4 is indeterminate or high, a second test – usually vibration-controlled transient elastography (FibroScan), which measures liver stiffness, or the Enhanced Liver Fibrosis (ELF) blood test.

The 2023 American Association for the Study of Liver Diseases (AASLD) guidance and the 2024 European EASL–EASD–EASO guideline both endorse this approach. In the UK, NICE recommends the ELF test for people with NAFLD and has encouraged FIB-4-based pathways in primary care.

Typical liver stiffness thresholds

These thresholds are approximate and vary between guidelines and populations.

Other non-invasive fibrosis scores

FIB-4 is one of several scores built from routine data:

• NAFLD Fibrosis Score (NFS): uses age, BMI, diabetes or impaired fasting glucose, AST/ALT ratio, platelets and albumin. It performs similarly to FIB-4 but needs more inputs, and its indeterminate range is wider.
• APRI (AST to Platelet Ratio Index): AST divided by its upper limit of normal, divided by platelets, multiplied by 100. It is used mainly in hepatitis C, particularly in resource-limited settings, as recommended by the World Health Organization.
• AST/ALT ratio: a ratio above 1 can suggest advanced fibrosis or alcohol-related liver disease, but it is less accurate on its own.
• ELF test: a patented blood test measuring three markers of matrix turnover (hyaluronic acid, PIIINP and TIMP-1). NICE recommends an ELF score of 10.51 or above to identify advanced fibrosis in NAFLD.
• Elastography: FibroScan, shear-wave elastography and magnetic resonance elastography measure liver stiffness directly.

Using two different types of test – a blood score and an imaging test – in sequence reduces both missed cases and unnecessary referrals.

FIB-4 in viral hepatitis

FIB-4 was first developed in hepatitis C and remains useful there. Before modern antiviral treatment, fibrosis staging determined who needed urgent treatment; today, almost everyone with hepatitis C is treated, but knowing whether cirrhosis is present still matters because people with cirrhosis need ongoing surveillance for liver cancer and complications even after cure. In hepatitis B, FIB-4 and elastography help decide who needs antiviral treatment, alongside viral load and ALT. In both conditions, active inflammation can raise AST and ALT and affect the score.

A primary care pathway: an example

A 58-year-old man with type 2 diabetes and a BMI of 32 has an ultrasound showing a fatty liver. His blood tests show AST 42 U/L, ALT 48 U/L and platelets 190 × 10⁹/L. His FIB-4 is (58 × 42) ÷ (190 × √48) = 2,436 ÷ 1,316 = 1.85 – indeterminate.

Following local guidance, his GP arranges an ELF test or FibroScan. His liver stiffness is 6.5 kPa, which makes advanced fibrosis unlikely. He continues in primary care with support for weight loss, diabetes and cardiovascular risk management, and a repeat FIB-4 in two to three years. If his liver stiffness had been above about 12 kPa, he would have been referred to a hepatologist for further assessment, including screening for liver cancer and varices if cirrhosis were confirmed.

Limitations of FIB-4

• Age under 35: FIB-4 performs poorly in young people and is not recommended for them.
• Age 65 and older: use the 2.0 lower cut-off to reduce false positives.
• Acute liver injury: very high AST and ALT from hepatitis, medicines or recent heavy drinking make the score unreliable.
• Low platelets from other causes: immune thrombocytopenia, bone marrow problems and some medicines lower platelets and inflate FIB-4.
• Muscle injury: AST is also released from muscle, so strenuous exercise or muscle disease can raise the score.
• Type 2 diabetes: some studies suggest lower accuracy in people with diabetes, who also have a higher baseline risk, so clinicians may have a lower threshold for further testing.
• Alcohol-related liver disease: FIB-4 can be used, but cut-offs are less well established.

Factors that affect the components

Ranges by age and sex

FIB-4 values tend to be higher in older people because age is part of the formula. Typical values in healthy adults are around 0.5–1.0 in middle age and around 1.0–1.6 in people over 65. Men and women use the same cut-offs, though normal ALT is usually lower in women; the American College of Gastroenterology suggests a healthy ALT upper limit of about 29–33 U/L in men and 19–25 U/L in women, lower than many laboratory ranges.

What happens if you are referred

If your FIB-4 and a second test suggest advanced fibrosis, a liver specialist will typically:

• review your medical history, alcohol intake, medicines and family history
• check for other causes of liver disease, such as viral hepatitis, haemochromatosis, autoimmune liver disease and Wilson's disease
• repeat or extend non-invasive testing, sometimes with magnetic resonance elastography
• occasionally recommend a liver biopsy when the diagnosis or stage is uncertain
• if cirrhosis is present, arrange liver cancer surveillance with ultrasound every six months and assess for varices
• discuss treatment options, including lifestyle support, medicines and clinical trials

Many people referred with an intermediate result are reassured and discharged back to primary care after assessment.

Reducing the risk of liver fibrosis

For people with MASLD, the main treatments target the underlying metabolic problems:

• Weight loss: losing 5% of body weight reduces liver fat; 7–10% can reduce inflammation; around 10% or more can improve fibrosis in some people.
• Physical activity: reduces liver fat even without weight loss.
• Diet: a Mediterranean-style pattern, fewer sugar-sweetened drinks and less ultra-processed food.
• Alcohol: avoiding or minimising alcohol, especially when fibrosis is present.
• Diabetes, blood pressure and lipid management, which also reduce cardiovascular risk – the leading cause of death in MASLD.
• Medicines: in 2024, the US FDA granted accelerated approval to resmetirom for adults with metabolic dysfunction-associated steatohepatitis (MASH) and moderate to advanced fibrosis. GLP-1 receptor agonists such as semaglutide have also shown benefit in trials.

Coffee drinking has been associated with lower rates of liver fibrosis in observational studies, though this does not prove cause and effect.

When to see a doctor

Discuss your FIB-4 with your clinician if it is indeterminate or high, if you have fatty liver on a scan, type 2 diabetes, obesity or persistently raised liver enzymes, or if you drink alcohol regularly. Seek prompt medical care for yellowing of the skin or eyes (jaundice), swelling of the abdomen or legs, vomiting blood, black stools, or confusion – signs that may indicate advanced liver disease.