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FIB-4 Index

A score worked out from your age, AST, ALT and platelet count. It helps estimate the chance of advanced scarring (fibrosis) in the liver.

AI-verified against cited sources. Awaiting expert reviewAlso called FIB-4, FIB4LOINC 98488-0

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What it is

FIB-4 is not a blood test on its own. It is a calculation that combines your age with three routine results: AST, ALT and platelet count. It helps estimate how likely it is that the liver has advanced scarring, called fibrosis. Scarring builds up slowly and often causes no symptoms. Some labs print the score with your liver tests, and clinicians can also work it out themselves.

Why it matters

Fatty liver disease is common, and many people with it do not develop serious scarring. FIB-4 is a simple, low-cost way to sort people into lower and higher chances of advanced fibrosis, using tests you may already have. A low score points to a lower chance, so many people can be followed in primary care. A higher score is a reason for a closer look with another test, not a result by itself.

If it’s low

A low score does not point to a problem. A score below 1.3 makes advanced scarring less likely, but it is not a guarantee, and it is less reliable in people under about 35.

Common causes

  • Younger age
  • AST and ALT in the usual range with a platelet count in the usual range
  • No advanced scarring in the liver

What can help

  • Ask how often your clinician would like to repeat it, based on your risk factors
  • Keep in touch with your clinician about weight, blood sugar, blood pressure and alcohol use

If it’s high

A higher score means a greater chance of advanced liver scarring, but it does not prove it. Between 1.3 and 2.67 the result is indeterminate, and above 2.67 the chance is higher. Many things besides scarring can raise the score, so your clinician will read it with your history and other tests.

Common causes

  • Older age, since age is part of the formula
  • A temporary rise in AST from hard exercise, muscle injury or an acute illness
  • A falsely low platelet count from platelets that clumped in the blood tube
  • Low platelets for other reasons, including some medicines
  • Fatty liver disease with scarring
  • Long-term alcohol-related liver disease
  • Chronic viral hepatitis

What can help

  • Ask about a follow-up test, such as a blood test called ELF or an elastography scan (for example FibroScan)
  • Ask whether your liver tests and platelet count should be repeated
  • Talk with your clinician about weight, physical activity and alcohol, which affect fatty liver disease

Usual ranges

What labs print as the reference range, by who was tested. Ranges differ a little between labs, so the range on your own report is the one your result is judged against.

The usual range depends on age. Choose an age to see the one that applies.

See FIB-4 by age and sex, with the U.S. survey numbers where they exist.

AASLD 2023 FIB-4 risk categories for advanced fibrosis (ages 18 to 64)

  • Lower riskbelow 1.3 index
  • Indeterminate1.3 to under 2.67 index
  • Higher risk2.67 and above index

FIB-4 cut-off for ages 65 and older (McPherson 2017)

  • Below the age 65+ cut-offbelow 2 index
  • At or above the age 65+ cut-off2 and above index

If this applies to you

FIB-4 means a little more for some people. Open the one that fits you.

Fatty liver or liver condition

FIB-4 combines age, ALT, AST and platelets into one score for liver scarring (fibrosis). AASLD uses it as the first check in people with fatty liver or risk factors, and suggests repeating it every 1 to 2 years with prediabetes, type 2 diabetes or two or more metabolic risk factors. A higher score leads to a second test such as elastography or ELF.

Blood tests for liver health

Prediabetes or diabetes

FIB-4 combines age, ALT, AST and platelets to estimate the chance of liver scarring from fatty liver disease. The ADA suggests it for adults with type 2 diabetes or prediabetes, especially with obesity or other heart and metabolic risk factors, even when liver enzymes are normal. A score of 1.3 or higher leads to a further test, such as a liver stiffness scan.

Blood tests for prediabetes and diabetes

What can affect your result

  • Age: it is part of the formula, and the cut-off changes at 65
  • Acute illness, hard exercise or muscle injury, which can raise AST
  • Platelet clumping in the tube, which can lower the platelet count falsely
  • Medicines or conditions that lower platelets
  • Lower accuracy under about 35
  • It is worked out from AST, ALT and platelets, so anything that changes those changes the score.
  • Hard exercise, muscle injury or an acute illness can raise AST, and a sudden illness can distort the score. AASLD says FIB-4 should not be used in acutely ill patients.
  • Platelets that clump in the blood tube can read falsely low, which raises the score.
  • Accuracy is lower under about 35 and over 65 with the standard cut-off.

Scarring changes slowly, over years. The score itself can move within weeks, because AST, ALT and platelets can change that quickly.

When to talk to a clinician

There is no urgent FIB-4 value. Talk with a clinician about a score of 1.3 or higher (2.0 or higher at 65 and older), so they can decide on a follow-up test. Get prompt care for yellow skin or eyes, vomiting blood, black or tarry stools, a swollen belly, or new confusion or drowsiness, and call 911 or your local emergency number if these are severe.

Questions you could ask

  • Which liver conditions does this score matter for in my case?
  • How does my score fit with my other liver tests?
  • Should I have a follow-up test, such as an ELF blood test or an elastography scan?
  • Could my age, a recent illness, exercise or a medicine be affecting my AST, ALT or platelets?
  • Should we repeat these tests, and how soon?
  • How often should this be rechecked, given my health conditions?

Questions people ask

Does a score between 1.3 and 2.67 mean I have scarring?

No. That range is called indeterminate. It means the score cannot say either way, and a second test, such as an ELF blood test or an elastography scan, is the usual next step.

Why is my cut-off 2.0 instead of 1.3?

The score rises with age, so many people over 65 who have no advanced scarring still score above 1.3. Guidance for older adults uses 2.0 as the cut-off to reduce unnecessary follow-up.

Can this score be wrong?

Yes. It is less reliable under about 35, during an acute illness and in people with certain other conditions, and anything that changes AST, ALT or platelets changes the score. It is a first step, not a final answer.

Show the science and sources

For clinicians and researchers

FIB-4 = (age [years] × AST [U/L]) / (platelets [10^9/L] × √ALT [U/L]). It was derived by Sterling et al. in 832 patients with HIV/HCV coinfection, with cut-offs of 1.45 and 3.25 against Ishak stage 4 to 6 (AUROC 0.765). In 541 adults with NAFLD (Shah 2009) the median was 1.11, ≤1.30 had a 90% negative predictive value, and ≥2.67 had an 80% positive predictive value for advanced fibrosis; AASLD 2023 uses 1.3 and 2.67 as rule-out and rule-in cut-offs and calls FIB-4 the most validated of the clinical scores. Age confounds it: McPherson 2017 found a specificity of only 35% at the 1.3 cut-off in people 65 and older, and a cut-off of 2.0 raised specificity to 70% (sensitivity 77%); performance was poor at 35 or younger (AUROC 0.60). AASLD advises a secondary assessment (preferably elastography or ELF) for FIB-4 of 1.3 or higher, says direct referral to a liver specialist should be considered above 2.67, and notes that these tests may be less robust in people with diabetes. Cut-offs are not interchangeable across etiologies, and the score is not designed for acute hepatitis.

LOINC 98488-0 (primary). Specimen: calculated.

Sources

  1. AASLD Practice Guidance on the clinical assessment and management of nonalcoholic fatty liver disease, Hepatology (AASLD) (2023)
  2. Development of a simple noninvasive index to predict significant fibrosis in patients with HIV/HCV coinfection, Hepatology (2006)
  3. Comparison of noninvasive markers of fibrosis in patients with nonalcoholic fatty liver disease, Clinical Gastroenterology and Hepatology (2009)
  4. Age as a Confounding Factor for the Accurate Non-Invasive Diagnosis of Advanced NAFLD Fibrosis, American Journal of Gastroenterology (2017)
  5. LOINC 98488-0 (NLM Clinical Tables), National Library of Medicine

AI-verified against cited sources. Awaiting expert review. Last reviewed 2026-10-03. How we build and check these pages.

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