Non-invasive detection of advanced liver fibrosis (F3–F4) in NAFLD/MASLD — using Age, BMI, Diabetes status, AST/ALT ratio, Platelets & Albumin. Validated AUROC 0.88 · NPV 93% · PPV 90%.
Impaired fasting glucose (100–125 mg/dL), pre-diabetes, or type 2 DM
Normal: 10–40 U/L
Normal: 7–56 U/L
Normal: 150–400 ×10⁹/L
Normal: 3.5–5.0 g/dL · If lab shows g/L, divide by 10
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Two cutoff points were validated by Angulo et al. (2007) in 733 NAFLD patients across multiple international centres, then independently replicated. The score distinguishes patients with F0–F2 (no/mild fibrosis) from those with F3–F4 (advanced fibrosis/cirrhosis) without requiring a liver biopsy.
| NFS Score | Category | Fibrosis Stage | NPV / PPV | Clinical Action |
|---|---|---|---|---|
| < −1.455 | 🟢 Low Risk | F0–F2 (Absent / Mild) | NPV 93% | Advanced fibrosis unlikely. Manage metabolic risk factors. Repeat NFS / FIB-4 in 1–2 years. |
| −1.455 to 0.675 | 🔵 Indeterminate | F1–F3 (Variable) | — | Additional testing needed: FibroScan (LSM), MR Elastography, ELF test, or liver biopsy. |
| > 0.675 | 🔴 High Risk | F3–F4 (Advanced / Cirrhosis) | PPV 90% | High probability of advanced fibrosis. Hepatology referral. Confirm with elastography or biopsy. Consider HCC surveillance. |
⚠️ Indeterminate Zone — Common in Clinical Practice
Up to 25–35% of NAFLD patients fall in the indeterminate range. This is not a failure of the score — it correctly reflects uncertainty and triggers appropriate escalation. Do not reassure or dismiss patients in this zone without further evaluation.
| Variable | Coefficient | Unit | Clinical Rationale |
|---|---|---|---|
| Constant | −1.675 | — | Model intercept; sets the baseline score |
| Age | +0.037 | years | Fibrosis accumulates with age; older patients have higher background risk |
| BMI | +0.094 | kg/m² | Obesity drives MASLD progression; higher BMI correlates with worse fibrosis |
| IFG / Diabetes | +1.13 | 1 or 0 | Strongest individual predictor; insulin resistance accelerates hepatic fibrogenesis |
| AST/ALT ratio | +0.99 | ratio | Ratio >1 suggests advanced fibrosis or cirrhosis; mitochondrial injury shifts to AST dominance |
| Platelet count | −0.013 | ×10⁹/L | Low platelets reflect portal hypertension / splenomegaly — markers of advanced fibrosis |
| Albumin | −0.66 | g/dL | Low albumin indicates impaired hepatic synthetic function, consistent with advanced disease |
Non-Alcoholic Fatty Liver Disease (NAFLD) — renamed MASLD (Metabolic dysfunction-Associated Steatotic Liver Disease) in the 2023 Delphi nomenclature consensus — is the most common chronic liver disease worldwide, affecting approximately 25% of the global adult population. In India, prevalence is estimated at 25–38% among urban adults and rising rapidly alongside the epidemic of obesity, type 2 diabetes, and metabolic syndrome.
MASLD encompasses a spectrum from simple steatosis (fat deposition without inflammation) through MASH (Metabolic dysfunction-Associated Steatohepatitis, formerly NASH) to advanced fibrosis and cirrhosis. The critical determinant of long-term prognosis is fibrosis stage — not the degree of steatosis or inflammation. Patients with F3–F4 fibrosis have significantly elevated risks of liver-related mortality, hepatocellular carcinoma (HCC), and need for liver transplantation.
Liver biopsy — the gold standard for fibrosis staging — is invasive, expensive, subject to sampling variability, and impractical for the millions of patients with MASLD. Non-invasive scoring systems like the NAFLD Fibrosis Score (NFS) and FIB-4 allow clinicians to stratify fibrosis risk using routine clinical and laboratory data, reserving biopsy or elastography for those in the indeterminate or high-risk zones.
In India, MASLD is increasingly encountered in primary care, general medicine, and gastroenterology outpatient settings. FibroScan availability is largely limited to metro tertiary centres. The NFS can be calculated from parameters available in any standard CBC + LFT + metabolic panel — investigations already ordered in most patients with deranged liver function or metabolic syndrome. Applying the NFS at point-of-care enables rational triaging: low-risk patients can be managed with lifestyle counselling; indeterminate/high-risk patients can be prioritised for FibroScan or hepatology referral.
Both NFS and FIB-4 are endorsed by EASL 2024 and AASLD 2023 MASLD guidelines. Current guidance recommends a sequential approach:
| Feature | NFS | FIB-4 |
|---|---|---|
| Variables | 6 (Age, BMI, DM, AST, ALT, Platelets, Albumin) | 4 (Age, AST, ALT, Platelets) |
| Specificity (F3–F4) | Higher (PPV 90%) | Moderate (PPV ~65%) |
| Sensitivity | Lower at high cutoff | Higher at low cutoff |
| Best Disease | NAFLD/MASLD (purpose-built) | HCV, HBV, NAFLD/MASLD |
| Guideline Role | Step 2 confirmatory test | Step 1 initial screening |
| Limitations | Needs BMI + Albumin + DM status | Less reliable age <35 / >65 |
The NAFLD Fibrosis Score (NFS) is a non-invasive clinical scoring system that estimates the likelihood of advanced hepatic fibrosis (F3–F4) in patients with Non-Alcoholic Fatty Liver Disease (NAFLD, now termed MASLD). It was developed by Angulo et al. in 2007 using six routinely available parameters: age, BMI, presence of impaired fasting glucose or diabetes, AST/ALT ratio, platelet count, and serum albumin. It was validated in 733 patients across multiple international centres, achieving an AUROC of 0.88.
NFS = −1.675 + (0.037 × Age [years]) + (0.094 × BMI [kg/m²]) + (1.13 × IFG/Diabetes [1=yes, 0=no]) + (0.99 × AST/ALT ratio) − (0.013 × Platelet count [×10⁹/L]) − (0.66 × Albumin [g/dL])
The score typically ranges from approximately −3 to +2. All six parameters are available from routine clinical assessment and standard blood tests.
NFS < −1.455 (Low Risk): Advanced fibrosis (F3–F4) is unlikely. Negative predictive value is 93%. Biopsy can be deferred; focus on metabolic risk factor management and annual monitoring.
NFS −1.455 to 0.675 (Indeterminate): The score cannot reliably classify fibrosis in this range. Further investigation is required: FibroScan, MR Elastography, ELF test, or liver biopsy.
NFS > 0.675 (High Risk): Advanced fibrosis or cirrhosis is likely. Positive predictive value is 90%. Hepatology referral is recommended; confirm staging with elastography or biopsy; initiate HCC surveillance if cirrhosis confirmed.
In the original validation study (Angulo et al., Hepatology 2007), the NFS achieved an AUROC of 0.88 (95% CI 0.85–0.92) for detecting advanced fibrosis (F3–F4). At the low cutoff (−1.455), the NPV was 93% — meaning that of patients below this threshold, 93% truly do not have advanced fibrosis. At the high cutoff (0.675), the PPV was 90% — meaning 9 in 10 patients above this threshold have confirmed advanced fibrosis. Subsequent external validations have broadly confirmed these figures, with some variation by population.
Both are validated non-invasive fibrosis scores for NAFLD/MASLD. FIB-4 uses only 4 variables (Age, AST, ALT, Platelets) and is simpler to calculate — it is recommended as the first-line screen. NFS uses 6 variables and has higher specificity at the high cutoff (PPV 90% vs FIB-4's ~65%), making it more valuable for confirming high-risk patients or clarifying indeterminate FIB-4 results. Current EASL 2024 and AASLD 2023 guidelines recommend using FIB-4 for initial screening, then NFS (or FibroScan) for those in the indeterminate FIB-4 zone (1.30–2.67).
IFG stands for Impaired Fasting Glucose — a fasting plasma glucose between 100–125 mg/dL (5.6–6.9 mmol/L). For the NFS, the IFG/Diabetes variable is scored as 1 (yes) if the patient has any of the following:
Score 0 (no) only if fasting glucose, HbA1c, and clinical history are all normal with no prior diagnosis. This is the most heavily weighted single variable in the formula (+1.13 coefficient), reflecting the central role of insulin resistance in MASLD fibrosis progression.
Yes. MASLD (Metabolic dysfunction-Associated Steatotic Liver Disease) is the updated nomenclature for NAFLD adopted by the multinational Delphi consensus in 2023. The patient population, pathophysiology, and fibrosis staging criteria are identical to those for which the NFS was developed and validated. The cutoffs, formula, and interpretation remain fully applicable. The renaming was a nosological and stigma-reduction exercise — not a change in disease biology.
Most Indian laboratory reports express serum albumin in g/dL. Normal serum albumin is 3.5–5.0 g/dL. Some internationally formatted lab reports (and some hospital information systems) use g/L — where normal is 35–50 g/L. To convert from g/L to g/dL, divide by 10 (e.g., 42 g/L = 4.2 g/dL). This calculator requires albumin in g/dL. If your lab reports in g/L, enter the value divided by 10.
The NFS has several important limitations:
For NFS in the indeterminate range (−1.455 to 0.675), the recommended next steps per EASL 2024 are: