Medical Calculators › Hepatology › Forns Index

Forns Index

Non-Invasive Index for Significant Hepatic Fibrosis (F2–F4)
Predicts significant hepatic fibrosis (Metavir F2–F4) using four routine blood tests: platelet count, GGT, age, and cholesterol. High NPV (96%) allows safe avoidance of liver biopsy in low-risk patients.
Hepatology Fibrosis Hepatitis C Non-invasive Liver Biopsy
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Forns Index
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Formula

Forns Index = 7.811
  − 3.131 × ln(Platelet ×10&sup9;/L)
  + 0.781 × ln(GGT U/L)
  + 3.467 × ln(Age years)
  − 0.014 × Cholesterol mg/dL

Uses natural logarithm (ln). If cholesterol in mmol/L, multiply by 38.67 to convert to mg/dL.

Interpretation

Forns Score Probability NPV / PPV Action
<4.2 Low probability F2–F4 NPV 96% Biopsy avoidable
4.2–6.9 Indeterminate — Consider additional testing
>6.9 High probability F2–F4 PPV 66% Biopsy recommended

Clinical Application

  • Validated in chronic hepatitis C (HCV genotype 1–4)
  • Can be used as a first-line screening test to identify patients who do not require biopsy
  • Comparison with FIB-4 and APRI: FIB-4 now preferred due to simplicity; Forns includes cholesterol
  • In the indeterminate zone, transient elastography (FibroScan) is recommended

Validation

  • Derivation cohort: 476 consecutive HCV patients; validation cohort: 302 patients
  • AUROC 0.86 for significant fibrosis (Metavir F2–F4)
  • 46% of patients could avoid biopsy with a Forns Index <4.2

Limitations

  • Validated primarily in HCV; limited data in NASH/NAFLD, alcoholic liver disease
  • Cholesterol is affected by diet, statin use, and liver disease severity itself
  • Less commonly used now with widespread availability of transient elastography

References

  1. Forns X, et al. Identification of chronic hepatitis C patients without hepatic fibrosis by a simple predictive model. Hepatology. 2002;36(4):986–992.