FIB-4 Worked Examples Across Risk Categories

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By Bikash Roy

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Bikash Roy

Online Research Specialist · SEO Strategist · Web Developer

Bikash personally verifies every calculator against official standards (WHO, NIH, government data). Online research specialist, SEO strategist, and web developer with 10+ years building accurate digital tools.

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· July 20, 2026

Four worked FIB-4 calculations spanning low, indeterminate, and high risk, plus a same-labs comparison showing the age-adjusted cutoff in action.

Example 1 — Low Risk, Younger Patient

Age 38, AST 28 U/L, ALT 32 U/L, Platelets 250 ×10⁹/L.

FIB-4 = (38 × 28) ÷ (250 × √32)
      = 1,064 ÷ (250 × 5.657)
      = 1,064 ÷ 1,414.2
      = 0.75

Well below the standard 1.30 low-risk cutoff — advanced fibrosis is unlikely, consistent with the strong negative predictive value FIB-4 carries at low scores.

Example 2 — Indeterminate, Middle-Aged Patient

Age 55, AST 60 U/L, ALT 45 U/L, Platelets 180 ×10⁹/L.

FIB-4 = (55 × 60) ÷ (180 × √45)
      = 3,300 ÷ (180 × 6.708)
      = 3,300 ÷ 1,207.4
      = 2.73

This lands just above the 2.67 high-risk threshold — close enough to the boundary that confirming the labs weren’t affected by a confounder (recent illness, medication) matters before treating it as a firm high-risk result. See common FIB-4 mistakes for what to check first.

Example 3 — Same Labs, Age-Adjusted Cutoff Changes the Category

Age 68, AST 35 U/L, ALT 40 U/L, Platelets 190 ×10⁹/L.

FIB-4 = (68 × 35) ÷ (190 × √40)
      = 2,380 ÷ (190 × 6.325)
      = 2,380 ÷ 1,201.7
      = 1.98

Under the standard below-1.30 cutoff, this would look indeterminate. But since the patient is 68, the age-adjusted low-risk cutoff (below 2.00) applies instead — and 1.98 falls just under it, landing in the low-risk category. This is exactly the scenario the age adjustment exists to correct: without it, this patient would be flagged for unnecessary follow-up testing based purely on age-related score inflation.

Example 4 — Clearly High Risk

Age 60, AST 95 U/L, ALT 40 U/L, Platelets 110 ×10⁹/L.

FIB-4 = (60 × 95) ÷ (110 × √40)
      = 5,700 ÷ (110 × 6.325)
      = 5,700 ÷ 695.7
      = 8.19

Well above the 2.67 high-risk threshold, with a notably low platelet count alongside elevated AST — a pattern consistent with more advanced disease, and a clear candidate for the hepatology referral pathway described in FIB-4 for primary care: when to refer to hepatology.

Running These Yourself

Every score above matches what the FIB-4 calculator produces from the same age, AST, ALT, and platelet inputs — enter real lab values to reproduce these results or check a scenario not covered here, and remember to apply the age-adjusted cutoff for any patient 65 or older.