Calculate the NAFLD Fibrosis Score (NFS) to assess liver fibrosis severity in fatty liver disease. Also computes FIB-4 and APRI for comparison.
The NAFLD Fibrosis Score (NFS) is a validated, non-invasive tool for identifying advanced liver fibrosis (F3-F4) in patients with non-alcoholic fatty liver disease (NAFLD), now renamed metabolic dysfunction-associated steatotic liver disease (MASLD). Using six readily available clinical and laboratory variables — age, BMI, diabetes status, AST/ALT ratio, platelet count, and albumin — it stratifies patients into low, indeterminate, and high probability of advanced fibrosis.
NAFLD/MASLD affects approximately 25-30% of the global adult population and is the leading cause of chronic liver disease in developed countries. While most patients have simple steatosis with benign prognosis, 10-15% progress to non-alcoholic steatohepatitis (NASH) and potentially cirrhosis. The critical clinical question is identifying the subset with advanced fibrosis, as they face significantly increased liver-related and overall mortality.
This calculator also provides FIB-4 and APRI scores for comparison, as current guidelines recommend using multiple non-invasive tests in a stepwise algorithm before proceeding to liver biopsy.
Liver biopsy, while the gold standard, is invasive, costly, subject to sampling error, and carries procedural risk (pain in 30%, significant complications in 0.5%). Non-invasive scores like NFS can reliably rule out advanced fibrosis (NPV >93% at the low cutoff), avoiding unnecessary biopsies in the majority of NAFLD patients.
Current AASLD and EASL guidelines recommend NFS or FIB-4 as first-line screening tools, with liver elastography (FibroScan) as a second-line test for patients in the indeterminate range.
NFS = −1.675 + 0.037 × age + 0.094 × BMI + 1.13 × IFG/Diabetes(yes=1) + 0.99 × AST/ALT ratio − 0.013 × platelets − 0.66 × albumin Low cutoff: < −1.455 → F0-F2 (NPV 93%) High cutoff: > 0.676 → F3-F4 (PPV 82%) FIB-4 = (Age × AST) / (Platelets × √ALT) APRI = ((AST / ULN) × 100) / Platelets
Result: NFS 0.45 — Indeterminate
The NFS of 0.45 falls in the indeterminate zone (-1.455 to 0.676). This means advanced fibrosis cannot be confidently ruled in or out by blood tests alone. The recommended next step is liver elastography (FibroScan); if elastography is also indeterminate, liver biopsy may be needed.
Histological fibrosis is staged F0-F4: F0 (no fibrosis), F1 (perisinusoidal/portal), F2 (perisinusoidal + portal), F3 (bridging fibrosis), F4 (cirrhosis). The clinical significance is primarily in distinguishing F0-F2 (low risk) from F3-F4 (significant liver-related mortality risk). Patients with F3-F4 fibrosis have a 10-year liver-related mortality of 10-25%.
All NAFLD patients should receive lifestyle counseling. For F0-F2: weight loss (7-10% body weight), exercise, and cardiometabolic risk factor management. For F3-F4: aggressive weight management, consideration of GLP-1 receptor agonists or resmetirom (recently FDA-approved for NASH with F2-F3 fibrosis), hepatocellular carcinoma surveillance, and variceal screening.
The recommended approach: Step 1 — NFS or FIB-4 (rules out advanced fibrosis in ~60% of patients). Step 2 — FibroScan or Enhanced Liver Fibrosis (ELF) test for indeterminate cases. Step 3 — Liver biopsy if non-invasive tests remain discordant or indeterminate. This algorithm avoids biopsy in approximately 70-80% of patients while maintaining diagnostic accuracy.
In 2023, a multi-society consensus renamed NAFLD to MASLD (metabolic dysfunction-associated steatotic liver disease). MASLD requires hepatic steatosis PLUS at least one cardiometabolic risk factor (BMI ≥25, diabetes, hypertension, dyslipidemia, waist circumference criteria). The NFS remains valid under both nomenclatures.
NFS and FIB-4 are blood-based scores ideal for initial screening (high NPV). FibroScan (transient elastography) provides a direct measurement of liver stiffness (in kPa) with better accuracy for intermediate-risk patients. Current guidelines recommend a sequential approach: NFS/FIB-4 first, then FibroScan for indeterminate cases.
NFS was specifically developed and validated for NAFLD/MASLD. It has not been validated in hepatitis B/C, alcoholic liver disease, autoimmune hepatitis, or other etiologies. FIB-4 has broader validation across multiple liver disease etiologies.
Approximately 25-35% of NAFLD patients fall in the indeterminate zone. These patients require additional testing — typically liver elastography. If FibroScan liver stiffness is <8 kPa, advanced fibrosis is unlikely; if >12 kPa, it is probable. Values 8-12 kPa may warrant biopsy.
Yes. NFS has lower specificity in patients over 65 years because age itself increases the score. Some authors suggest using an adjusted high cutoff of >0.12 instead of >0.676 for patients >65 years to reduce false positives.
For patients with low NFS: repeat every 3-5 years unless clinical status changes. For indeterminate or high NFS patients under treatment: repeat every 1-2 years to assess treatment response. Improvement in NFS (moving from high to indeterminate or low) correlates with histological regression.