FIB-4 Score Calculator

FIB-4 Score Calculator for Gastroenterology. The widely used MASLD/NAFLD thresholds define three bands. Below 1.30, advanced fibrosis (stage F3-F4) is effectively ruled out with a high negative predictive value (roughly 90 percent), and these patients can be managed in primary care with lifestyle intervention and periodic rescreening. Above 2.67 (some pathways use 3.25), advanced fibrosis is likely and specialist referral plus elastography or biopsy is indicated. The 1.30 to 2.67 middle zone is genuinely indeterminate, capturing a large fraction of patients, and should trigger a second-line test (FibroScan or ELF) rather than a decision either way. In patients over 65, raise the lower cutoff to 2.0 to preserve specificity.

How this calculator works

FIB-4 combines four routinely available variables into a single dimensionless number: FIB-4 = (Age in years x AST) / (Platelet count in 10^9/L x square root of ALT). Aminotransferases are entered in U/L. Because AST sits in the numerator and platelets in the denominator, the index rises with the same biochemical signature that accompanies advancing fibrosis: relative AST elevation and a falling platelet count from portal hypertension. It is a surrogate for the histologic fibrosis stage, not a direct measurement.

When to use this calculator

FIB-4 is a first-line, point-of-care filter to decide who needs specialist referral or elastography in chronic liver disease, most heavily used today for metabolic dysfunction-associated steatotic liver disease (MASLD/NAFLD) and originally derived in HIV/HCV coinfection. It suits primary care, endocrine, and diabetes clinics screening at-risk populations. It performs poorly and should not be trusted at the extremes of age: it over-classifies patients under 35 and loses specificity over 65, where a higher indeterminate cutoff (2.0) is preferred. Avoid it during acute hepatitis or any acute AST/ALT spike, and it is not a standalone diagnosis of cirrhosis.

Inputs used

  • Age
  • AST
  • ALT
  • Platelet count

Clinical interpretation

The widely used MASLD/NAFLD thresholds define three bands. Below 1.30, advanced fibrosis (stage F3-F4) is effectively ruled out with a high negative predictive value (roughly 90 percent), and these patients can be managed in primary care with lifestyle intervention and periodic rescreening. Above 2.67 (some pathways use 3.25), advanced fibrosis is likely and specialist referral plus elastography or biopsy is indicated. The 1.30 to 2.67 middle zone is genuinely indeterminate, capturing a large fraction of patients, and should trigger a second-line test (FibroScan or ELF) rather than a decision either way. In patients over 65, raise the lower cutoff to 2.0 to preserve specificity.

Worked example

A 58-year-old with type 2 diabetes has AST 46 U/L, ALT 30 U/L, and platelets 180 x 10^9/L. FIB-4 = (58 x 46) / (180 x sqrt(30)) = 2668 / (180 x 5.48) = 2668 / 986 = 2.71. Since 2.71 exceeds the 2.67 high cutoff, this falls in the high-risk band: advanced fibrosis is likely, so the patient warrants hepatology referral and confirmatory vibration-controlled transient elastography (FibroScan) rather than reassurance.

Limitations and safety notes

FIB-4 is confounded by anything that independently moves its inputs: thrombocytopenia from splenic sequestration, chemotherapy, ITP, or alcohol shifts the score up regardless of fibrosis, while a normal platelet count can mask early cirrhosis. Age is baked into the formula, so young patients are systematically pushed toward low scores and elderly patients toward high scores, degrading accuracy at both ends. Acute hepatitis, hemolysis, or muscle injury elevating AST produces spuriously high values. The indeterminate zone is large (up to a third of screened cohorts), so FIB-4 rules disease out better than it rules it in, and it cannot distinguish F3 from established F4 cirrhosis.

Frequently asked questions

What FIB-4 value rules out advanced fibrosis?

A score below 1.30 has a high negative predictive value (around 90 percent) for stage F3-F4 fibrosis and lets most patients avoid referral. In patients over 65, use 2.0 rather than 1.30 as the lower cutoff because specificity falls with age.

Why does the same patient's score change as they age?

Age is a direct multiplier in the numerator, so an identical AST, ALT, and platelet profile yields a higher FIB-4 in an older person. This is why the tool over-calls fibrosis after 65 and under-calls it before 35, and why age-adjusted cutoffs exist.

Do I plug ALT under the square root?

Yes. The denominator is platelets multiplied by the square root of ALT, while AST is used un-transformed in the numerator. Swapping AST and ALT or forgetting the square root is the most common calculation error.

Can FIB-4 diagnose cirrhosis?

No. A high score flags likely advanced fibrosis and mandates confirmatory testing such as transient elastography, ELF, or biopsy. FIB-4 cannot separate bridging fibrosis (F3) from cirrhosis (F4) and should never be the sole basis for a cirrhosis diagnosis.

Does FIB-4 work outside hepatitis C and MASLD?

It was derived in HIV/HCV coinfection and best validated in HCV and MASLD. It is less reliable in alcohol-associated liver disease, autoimmune hepatitis, and cholestatic diseases, and is unreliable when platelets or transaminases are altered by an unrelated cause.

References

  • Sterling RK, Lissen E, Clumeck N, et al. Development of a simple noninvasive index to predict significant fibrosis in patients with HIV/HCV coinfection. Hepatology. 2006;43(6):1317-25. PMID: 16729309.
  • Vallet-Pichard A, Mallet V, Nalpas B, et al. FIB-4: an inexpensive and accurate marker of fibrosis in HCV infection. Comparison with liver biopsy and FibroTest. Hepatology. 2007;46(1):32-6. PMID: 17567829.
  • Kanwal F, Shubrook JH, Adams LA, et al. Clinical Care Pathway for the Risk Stratification and Management of Patients With Nonalcoholic Fatty Liver Disease. Gastroenterology. 2021;161(5):1657-1669. PMID: 34602251.

Editorial review and citation methodology

Reviewed by the Quick Medical Calculator Editorial Team. Last reviewed: March 20, 2026. The review checks calculator inputs, intended population, interpretation, limitations, and source alignment.

  • Prefer original validation studies for scoring systems and prediction tools.
  • Use current specialty society guidance, transplant allocation policy, public health guidance, or regulator resources when they govern clinical use.
  • Include limitations and safety notes when a calculator is population-specific, context-dependent, or unsuitable as a standalone decision tool.

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