Hepatology

FIB-4 Calculator: Liver Fibrosis Index (Age, AST, ALT, Platelets)

Q: FIB-4 vs APRI — which to choose?

In NAFLD and in older patients, FIB-4 is more accurate. In HCV, both perform similarly. In practice, both are often calculated and compared.

Q: What threshold should be used in older patients?

In patients > 65 years, the low-risk threshold is shifted to 2.0 (instead of 1.3). This reflects the physiologic decline in platelet count with age.

Liver fibrosis index based on age, AST, ALT, and platelet count

Primary source: Sterling RK et al. Hepatology 2006; 43(6): 1317-1325

Aleksandr A. Aulov, MD, internal medicine Last clinical review: April 28, 2026

Online calculation

Age

years

AST

U/L

ALT

U/L

Platelets

×10⁹/L

About this score

The FIB-4 index (Sterling RK et al., Hepatology 2006) is a noninvasive marker of liver fibrosis, more accurate than APRI in older patients and in NAFLD. Formula: FIB-4 = (age × AST) / (platelets × √ALT).

Interpretation in NAFLD and HCV: < 1.3 (threshold 2.0 in patients > 65 years) — low probability of significant fibrosis, observation is sufficient; 1.3–2.67 — gray zone, additional testing needed; > 2.67 — increased probability of significant fibrosis or cirrhosis. Negative predictive value for excluding cirrhosis > 90%.

FIB-4 performs particularly well in primary care as a screening tool for NAFLD — it reliably excludes significant fibrosis in most patients and identifies only those who truly need FibroScan or biopsy. EASL 2024 and AASLD 2023 guidelines recommend FIB-4 as the first step in fibrosis workup.

When to use

Screening for fibrosis in NAFLD — standard of care in primary care.
Chronic viral hepatitis (HCV, HBV) — used alongside APRI.
Alcohol-related liver disease — assessment of chronic fibrosis.
Serial monitoring of disease progression.

Clinical example

Case

58-year-old man with type 2 diabetes, BMI 32, hepatic steatosis on ultrasound. AST 65 U/L, ALT 80 U/L, platelets 220×10⁹/L.

Calculation

FIB-4 = (58 × 65) / (220 × √80) = 3770 / (220 × 8.94) = 3770 / 1967 ≈ 1.92.

Interpretation and management

FIB-4 1.92 — gray zone. Approach: refer for FibroScan to assess fibrosis stage (if available) or reassess in 6 months with other markers. In parallel: lifestyle modification (7–10% weight loss significantly improves liver status), optimization of glycemic control and lipids, discussion of SGLT2 inhibitors or GLP-1 agonists (pioglitazone and liraglutide have evidence in NASH).

Limitations and cautions

In patients > 65 years, requires an adjusted threshold (< 2.0), otherwise overstratification occurs.
In patients with active hepatitis (markedly elevated AST/ALT), accuracy decreases.
Does not distinguish compensated cirrhosis from advanced F3 fibrosis.
The gray zone (1.3–2.67) includes a substantial proportion of patients.

Frequently asked questions

FIB-4 vs APRI — which to choose?

In NAFLD and in older patients, FIB-4 is more accurate. In HCV, both perform similarly. In practice, both are often calculated and compared.

What threshold should be used in older patients?

In patients > 65 years, the low-risk threshold is shifted to 2.0 (instead of 1.3). This reflects the physiologic decline in platelet count with age.

Does FIB-4 change with weight loss?

Yes, in patients with NASH, a 7–10% weight loss significantly improves FIB-4 and AST/ALT over 6–12 months.

At what FIB-4 value is biopsy indicated?

Biopsy is rarely indicated on the basis of FIB-4 alone. FibroScan is the first step; biopsy is considered when FIB-4 > 2.67 combined with FibroScan F3–F4, or when findings are discordant.

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Aleksandr A. Aulov Physician, internal medicine, Sechenov School — independent medical education platform. Calculators are compiled from the original publications and current clinical guidelines. Interpretation thresholds follow the source study unless stated otherwise.

This calculator is intended for healthcare professionals. Do not use it for self-diagnosis or self-treatment. Management decisions are made by the treating clinician based on the full clinical picture of the individual patient.