# FIB-4 Index Calculator (Liver Fibrosis)

Calculate FIB-4 index for liver fibrosis risk from age, AST, ALT, and platelets. Non-invasive screening tool recommended by AASLD and EASL guidelines.

## What this calculates

The FIB-4 index is a simple, non-invasive scoring system that estimates the degree of liver fibrosis using four routine lab values: age, AST, ALT, and platelet count. It is recommended by the AASLD and EASL as a first-line screening tool and can often eliminate the need for liver biopsy.

## Inputs

- **Age** (years) — min 18, max 120
- **AST (SGOT)** (U/L) — min 1, max 5000 — Aspartate aminotransferase. Normal: 10-40 U/L
- **ALT (SGPT)** (U/L) — min 1, max 5000 — Alanine aminotransferase. Normal: 7-56 U/L
- **Platelet Count** (10⁹/L) — min 1, max 1000 — Normal range: 150-400 x 10⁹/L

## Outputs

- **FIB-4 Index** — FIB-4 = (Age x AST) / (Platelets x √ALT)
- **Fibrosis Risk** — formatted as text — Likelihood of advanced fibrosis (F3-F4)
- **Recommended Next Step** — formatted as text — Clinical guidance based on score

## Details

The FIB-4 formula is: **FIB-4 = (Age x AST) / (Platelet Count x √ALT)**

Originally developed and validated in HIV/HCV co-infected patients, FIB-4 has since been validated across a wide range of chronic liver diseases including non-alcoholic fatty liver disease (NAFLD/MASH), chronic hepatitis B and C, and alcoholic liver disease. It is now one of the most widely used non-invasive fibrosis markers in clinical practice.

**Interpreting FIB-4 scores:**

- **Below 1.30 (or below 2.0 for age 65+):** Low risk of advanced fibrosis. The negative predictive value is approximately 90%, meaning 9 out of 10 patients in this range do not have significant fibrosis. No additional fibrosis workup is usually needed.
- **1.30 to 2.67 (indeterminate):** Further testing is recommended. Transient elastography (FibroScan) is the most common next step.
- **Above 2.67:** High probability of advanced fibrosis (F3-F4). Hepatology referral and confirmatory testing should be pursued.

**Why age-adjusted cutoffs matter:** The standard low cutoff of 1.30 has reduced specificity in patients over 65 because age is in the numerator, pushing scores higher regardless of fibrosis status. Using a higher cutoff of 2.0 for older patients improves specificity without meaningfully reducing sensitivity.

**Limitations:** FIB-4 can be falsely elevated in acute hepatitis (transient AST spikes), hemolytic conditions (falsely low platelets or elevated AST), and after heavy exercise. It should be calculated using stable, non-acute lab values.

**Disclaimer:** This calculator is for educational purposes. Fibrosis assessment and management decisions should be made in consultation with a gastroenterologist or hepatologist.

## Frequently Asked Questions

**Q: What does the FIB-4 score actually tell me?**

A: FIB-4 estimates whether you have advanced liver fibrosis (stages F3-F4 on a scale of F0-F4, where F4 is cirrhosis). It does not diagnose the cause of liver disease or tell you the exact fibrosis stage. Think of it as a screening test: a low score reliably rules out advanced fibrosis, while a high score warrants further investigation. It is most useful for deciding who needs additional workup and who can be safely monitored.

**Q: Can FIB-4 replace a liver biopsy?**

A: In many cases, yes. Current guidelines from the AASLD and EASL recommend FIB-4 as a first-line assessment, with liver biopsy reserved for cases where non-invasive tests are indeterminate or discordant. For patients with a clearly low FIB-4 (below 1.30), biopsy is generally not needed. For indeterminate or high scores, adding FibroScan often provides enough information to avoid biopsy. However, biopsy remains the gold standard when the diagnosis is uncertain or when grading inflammation is clinically important.

**Q: How often should I recheck FIB-4?**

A: For patients with ongoing liver disease risk factors (NAFLD, hepatitis, heavy alcohol use), rechecking FIB-4 every 1-2 years is reasonable if the initial score was low. If you are in the indeterminate zone and further testing was inconclusive, annual monitoring may be appropriate. A rising FIB-4 trend over time is more informative than any single value.

**Q: My AST and ALT are normal but FIB-4 is elevated. Is that possible?**

A: Yes. FIB-4 can be elevated even with normal transaminases, especially in older patients or those with low platelet counts. Normal ALT does not rule out fibrosis. In fact, many patients with NAFLD-related cirrhosis have persistently normal ALT levels. If your FIB-4 is elevated despite normal liver enzymes, further evaluation is still warranted.

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Source: https://vastcalc.com/calculators/health/fib-4
Category: Health & Fitness
Last updated: 2026-04-08