- Enter age (years), AST and ALT (U/L), and the platelet count (×10⁹/L). These four values compute the FIB-4 index instantly.
- To also compute the NAFLD Fibrosis Score (NFS), add the BMI (enter it directly, or supply height and weight to derive it), whether the patient has impaired fasting glucose or diabetes, and the serum albumin (g/dL).
- Read each score's category — low (rules out advanced fibrosis), indeterminate, or high (advanced fibrosis likely). The result box is coloured by the higher-risk of the two scores.
- A low score on both reliably rules out advanced fibrosis (F3–F4). A high or indeterminate score should prompt liver elastography (FibroScan/VCTE) or hepatology referral.
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When to Use
Use FIB-4 and the NAFLD Fibrosis Score as the first-line, non-invasive triage for advanced liver fibrosis in any adult with NAFLD/MASLD (hepatic steatosis on imaging or biopsy, with cardiometabolic risk factors). Their main value is their high negative predictive value: a low score reliably rules out advanced fibrosis (F3–F4) and lets you safely defer further testing. High or indeterminate scores identify the patients who warrant liver elastography or hepatology referral.
Appropriate population
Adults with known or suspected NAFLD/MASLD — including the cardiovascular–kidney–metabolic population you see in nephrology practice, where steatotic liver disease clusters with chronic kidney disease, type 2 diabetes, obesity, hypertension, and dyslipidemia. Both scores use routinely available labs (age, AST, ALT, platelets; NFS adds BMI, glucose/diabetes status, and albumin), so they can be applied opportunistically in clinic.
When NOT to rely on it
These scores are validated for chronic NAFLD/MASLD, not for acute liver injury. Do not apply them in acute hepatitis (the transient AST/ALT surge distorts the result), and interpret with caution at the extremes of age — performance falls in patients under ~35 and over ~65, where the standard cut-offs misclassify (use the age-adjusted cut-offs noted below). Any other cause of thrombocytopenia (hypersplenism, marrow disease, ITP, drugs) will inflate the score independent of fibrosis.
Pearls & Pitfalls
Low score = a confident rule-out
The strength of both indices is exclusion, not confirmation. A FIB-4 < 1.30 and an NFS < −1.455 have a high negative predictive value for advanced fibrosis, so a patient who is low on both can usually be reassured and followed conservatively. The indices are a triage step that spares most patients from elastography or biopsy — not a diagnosis of fibrosis on their own.
Age changes the low cut-off
In patients older than 65, the standard low FIB-4 cut-off of 1.30 over-calls fibrosis; use a low cut-off of 2.0 instead to preserve specificity. The NFS likewise has an age-adjusted lower threshold (≈ −0.12) in older patients. This calculator flags when the patient is over 65 so the result is read against the right band.
Pitfalls
(1) The indeterminate ("grey zone") band is common — these patients are not cleared and should move on to elastography (VCTE) or hepatology, not be ignored. (2) Both scores depend on the platelet count, so any non-hepatic cause of thrombocytopenia falsely raises them. (3) Not valid in acute hepatitis or other causes of acute transaminitis. (4) Reduced accuracy at age extremes. (5) The scores estimate the stage of fibrosis risk; they do not establish the etiology — confirm the diagnosis of MASLD clinically.
Why Use It
Advanced fibrosis (F3–F4) is the single strongest predictor of liver-related and overall mortality in NAFLD/MASLD, yet most patients have early-stage disease that needs no intervention — so the clinical problem is finding the few who are at risk without subjecting everyone to biopsy. FIB-4 and the NAFLD Fibrosis Score solve this with routine labs: they reliably rule out advanced fibrosis in the majority and concentrate further testing (elastography, hepatology referral, eventually biopsy) on the high and indeterminate groups. For a nephrology practice this matters because MASLD travels with CKD, diabetes, and obesity in the cardiovascular–kidney–metabolic syndrome — the same patients you already follow are exactly the ones in whom silent advanced liver fibrosis should be screened out.
FIB-4 & NAFLD Fibrosis Score — Liver Fibrosis Risk
Enter age, AST, ALT, and platelets for the FIB-4 index. Add BMI (or height + weight), glucose/diabetes status, and albumin to also compute the NAFLD Fibrosis Score (NFS). The result box is coloured by the higher-risk of the two scores.
Additional inputs for the NAFLD Fibrosis Score (NFS)
⚕ FIB-4 (Sterling RK, et al. Hepatology. 2006) and the NAFLD Fibrosis Score (Angulo P, et al. Hepatology. 2007) are non-invasive estimates of advanced fibrosis (F3–F4) risk in NAFLD/MASLD, per AASLD guidance (Rinella ME, et al. Hepatology. 2023). A low score rules out advanced fibrosis; high or indeterminate scores warrant elastography (VCTE) or hepatology referral. Not valid in acute hepatitis; less reliable at age extremes; thrombocytopenia from other causes inflates the score. For licensed clinicians; not a substitute for individualized assessment.
Next Steps
Use the two scores together to decide who can be reassured and who needs further liver assessment.
- Both scores low (FIB-4 < 1.30 and NFS < −1.455): advanced fibrosis is reliably ruled out. Reassure, treat the cardiometabolic risk factors, and re-assess periodically (e.g., every 1–3 years) as the disease evolves.
- Either score indeterminate (FIB-4 1.30–2.67 or NFS −1.455 to 0.675): the grey zone — do not clear these patients. Proceed to liver elastography (FibroScan/VCTE) or another second-line test to refine the risk.
- Either score high (FIB-4 > 2.67 or NFS > 0.675): advanced fibrosis is likely. Refer to hepatology, confirm with elastography ± biopsy, and screen for complications of cirrhosis where indicated.
- In patients over 65, read FIB-4 against the higher low cut-off (2.0) and the NFS against its age-adjusted threshold (≈ −0.12) to avoid over-calling fibrosis.
- Optimise the shared cardiometabolic drivers — pair this with your assessment of diabetes and the kidneys and overall metabolic syndrome in CKD.
Evidence & References
Formulas
| Score | Formula |
|---|---|
| FIB-4 index | (age × AST) ÷ (platelets × √ALT) |
| NAFLD Fibrosis Score (NFS) | −1.675 + 0.037×age + 0.094×BMI + 1.13×(IFG/DM ? 1 : 0) + 0.99×(AST/ALT) − 0.013×platelets − 0.66×albumin |
Interpretation — FIB-4
| FIB-4 value | Advanced fibrosis (F3–F4) risk |
|---|---|
| < 1.30 (or < 2.0 if age >65) | Low — high NPV, advanced fibrosis ruled out |
| 1.30–2.67 | Indeterminate — proceed to elastography |
| > 2.67 | High — advanced fibrosis likely; refer |
Interpretation — NAFLD Fibrosis Score
| NFS value | Stage / risk |
|---|---|
| < −1.455 (lower cut-off ≈ −0.12 if age >65) | F0–F2 (low) — advanced fibrosis unlikely |
| −1.455 to 0.675 | Indeterminate — proceed to elastography |
| > 0.675 | F3–F4 (advanced fibrosis) — refer |
Both indices were derived and validated against liver histology and are endorsed by AASLD guidance as the first-line non-invasive triage for advanced fibrosis in NAFLD/MASLD, with low scores used to safely rule it out and high/indeterminate scores escalated to elastography or specialist referral.
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):1317–1325.
- Angulo P, Hui JM, Marchesini G, et al. The NAFLD fibrosis score: a noninvasive system that identifies liver fibrosis in patients with NAFLD. Hepatology. 2007;45(4):846–854.
- Rinella ME, Neuschwander-Tetri BA, Siddiqui MS, et al. AASLD Practice Guidance on the clinical assessment and management of nonalcoholic fatty liver disease. Hepatology. 2023;77(5):1797–1835.
