NAFLD Fibrosis Score Calculator

NAFLD Fibrosis Score Calculator for Gastroenterology. Two validated cutoffs create three bands. A score below -1.455 is the low band, effectively ruling out advanced fibrosis (negative predictive value roughly 88-93%); these patients can usually be managed with metabolic risk-factor control without further fibrosis imaging. A score above 0.676 is the high band, ruling in advanced fibrosis (positive predictive value roughly 82-90%), and should prompt elastography and/or specialist referral. Scores between -1.455 and 0.676 are indeterminate and require a second-line test such as vibration-controlled transient elastography (liver stiffness) rather than a treatment decision on the NFS alone.

How this calculator works

The NAFLD Fibrosis Score (NFS) combines six routinely available variables into a single regression-derived value: age (years), body mass index, impaired fasting glucose or diabetes (yes/no), platelet count, serum albumin, and the AST/ALT ratio. The published equation is NFS = -1.675 + 0.037 x age + 0.094 x BMI + 1.13 x (IFG/diabetes = 1) + 0.99 x (AST/ALT ratio) - 0.013 x platelets (x10^9/L) - 0.66 x albumin (g/dL). Higher values reflect a greater probability of advanced (bridging) fibrosis or cirrhosis (histologic stage F3-F4). It was built and internally validated on 733 biopsy-proven NAFLD patients.

When to use this calculator

Use the NFS as a first-line, no-cost triage step to risk-stratify adults with established or suspected NAFLD/MASLD for advanced fibrosis, particularly those with metabolic risk factors (type 2 diabetes, obesity, metabolic syndrome). It is designed to decide who can be reassured versus who needs onward testing (elastography or specialist referral), not to make a standalone histologic diagnosis. It should not be applied to acute or decompensated liver disease, to significant alcohol-related or viral liver disease, or as a substitute for biopsy when the diagnosis itself is uncertain.

Inputs used

  • Age
  • BMI
  • Diabetes or impaired fasting glucose
  • AST
  • ALT
  • Platelet count
  • Albumin

Clinical interpretation

Two validated cutoffs create three bands. A score below -1.455 is the low band, effectively ruling out advanced fibrosis (negative predictive value roughly 88-93%); these patients can usually be managed with metabolic risk-factor control without further fibrosis imaging. A score above 0.676 is the high band, ruling in advanced fibrosis (positive predictive value roughly 82-90%), and should prompt elastography and/or specialist referral. Scores between -1.455 and 0.676 are indeterminate and require a second-line test such as vibration-controlled transient elastography (liver stiffness) rather than a treatment decision on the NFS alone.

Worked example

A 58-year-old with type 2 diabetes, BMI 33, platelets 180 x10^9/L, albumin 4.0 g/dL, AST 45, ALT 30 (AST/ALT ratio 1.5): NFS = -1.675 + 0.037(58) + 0.094(33) + 1.13(1) + 0.99(1.5) - 0.013(180) - 0.66(4.0) = -1.675 + 2.146 + 3.102 + 1.13 + 1.485 - 2.34 - 2.64 = 1.21. Because 1.21 exceeds the high cutoff of 0.676, this patient falls in the high-probability band for advanced fibrosis and warrants elastography and hepatology referral.

Limitations and safety notes

Roughly a quarter to a third of patients land in the indeterminate zone, where the score gives no actionable answer and elastography is needed. Because age carries substantial weight in the formula, the NFS over-classifies advanced fibrosis in patients over about 65 (specificity falls) and can under-perform in the young; some groups apply a raised low cutoff (around 0.12) above age 65. Albumin, platelets, and the AST/ALT ratio are also perturbed by conditions unrelated to hepatic fibrosis (systemic inflammation, hypersplenism, nutritional state, other liver disease), which degrades accuracy in those settings; the score was not validated in pediatric NAFLD.

Frequently asked questions

How does the NFS differ from FIB-4?

Both are simple serum-based fibrosis scores using age, AST, ALT, and platelets, but the NFS additionally incorporates BMI, albumin, and diabetes/impaired fasting glucose status. FIB-4 is often used first because it needs no anthropometric data; many pathways use the two together or use FIB-4 to triage and reserve elastography for indeterminate results. Neither replaces the other, and current guidance favors FIB-4 as the initial step with imaging confirmation.

What do I do with an indeterminate NFS?

An indeterminate score (between -1.455 and 0.676) is not a null result to ignore. It signals that serum markers alone cannot resolve the fibrosis question, so proceed to a second-line test, most commonly vibration-controlled transient elastography, or refer to hepatology. Do not start or withhold treatment based on an indeterminate value.

Should I adjust the cutoffs for older patients?

Yes, be cautious above roughly age 65. Because age is a strong positive term in the equation, older adults are frequently pushed above the low cutoff purely by age, lowering specificity. Some centers raise the lower threshold (for example to about 0.12) in patients over 65 to preserve rule-out performance, but any adjustment should follow local protocol and be paired with imaging.

Can the NFS be used to diagnose NASH or steatosis?

No. The NFS estimates only the probability of advanced fibrosis (F3-F4). It does not detect steatohepatitis (NASH/MASH), grade inflammation, or quantify steatosis, and a low score does not exclude milder fibrosis or active steatohepatitis. Those questions require histology or dedicated imaging/biomarker panels.

References

  • Angulo P, Hui JM, Marchesini G, Bugianesi E, George J, Farrell GC, et al. The NAFLD fibrosis score: a noninvasive system that identifies liver fibrosis in patients with NAFLD. Hepatology. 2007. PMID: 17393509.
  • Rinella ME, Neuschwander-Tetri BA, Siddiqui MS, Abdelmalek MF, Caldwell S, Barb D, Kleiner DE, Loomba R. AASLD Practice Guidance on the clinical assessment and management of nonalcoholic fatty liver disease. Hepatology. 2023. PMID: 36727674.

Editorial review and citation methodology

Reviewed by the Quick Medical Calculator Editorial Team. Last reviewed: April 19, 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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