Lab Values Entered
Four numbers start the fibrosis risk calculation.
- 58 yrs: Age (fixed patient value)
- variable: ALT (alanine transaminase)
- variable: AST (aspartate transaminase)
- variable: Platelets (×10⁹/L count)
Why these four values
Age and platelets track slow liver scarring changes.
ALT and AST reflect active liver cell injury.
No biopsy needed — just a routine blood panel.
Where the numbers come from
Standard complete blood count and liver panel.
Ordered during routine NAFLD screening visits.
Who gets screened
Adults with obesity, diabetes, or fatty liver on imaging.
Early screening catches fibrosis before symptoms appear.
FIB-4 Formula Applied
A simple ratio turns four labs into one score.
- Age×AST: Formula (÷ (Plt×√ALT))
- 2006: Published (Sterling et al.)
- HIV/HCV: Validated in (now used in NAFLD)
- ~$0: Cost (uses existing labs)
Reading the formula
Higher AST and age push the score up.
Higher platelets and ALT pull the score down.
Platelets fall as scarring worsens portal blood flow.
Why square root of ALT
Dampens the effect of large ALT swings.
Keeps the score stable across lab variability.
NAFLD Fibrosis Score
A second formula adds BMI, diabetes, and albumin.
Both scores are compared for a fuller picture.
Low-Risk Zone
A FIB-4 under 1.3 means fibrosis is unlikely.
- <1.3: Threshold (low-risk cutoff)
- ~90%: NPV (rules out advanced fibrosis)
- Routine: Action (follow-up in 1–3 years)
- ~70%: Biopsy avoided (of screened patients)
What low risk means
Advanced scarring is very unlikely at this stage.
Routine monitoring replaces invasive testing.
Most FIB-4 scores in primary care fall here.
Next steps
Lifestyle counseling and periodic re-testing.
Weight loss and metabolic control remain key.
Caveats
Very young or elderly patients need adjusted cutoffs.
FIB-4 is less reliable outside ages 35–65.
Indeterminate Zone
A score between 1.3 and 2.67 is inconclusive.
- 1.3–2.67: Range (gray zone)
- ~30%: Patients affected (of those screened)
- Elastography: Next test (or repeat labs)
- High: Uncertainty (needs more data)
Why the gray zone exists
FIB-4 alone cannot separate mild from advanced disease here.
A second, more specific test is needed.
This zone is the main reason for follow-up imaging.
Common follow-up tests
Vibration-controlled transient elastography (FibroScan).
Magnetic resonance elastography for higher precision.
Repeat testing
Labs can be repeated after treating other conditions.
Acute illness or fasting status can skew results.
High-Risk Zone
A FIB-4 above 2.67 flags likely advanced fibrosis.
- >2.67: Threshold (high-risk cutoff)
- ~80%: PPV (for advanced fibrosis)
- Refer: Action (to hepatology + elastography)
- Elevated: Cirrhosis risk (monitor closely)
What high risk means
Significant scarring is likely present.
Specialist referral is recommended promptly.
Elastography or biopsy confirms the fibrosis stage.
Clinical pathway
Hepatology referral for staging and management.
Screening for varices and hepatocellular carcinoma begins.
Why act early
Cirrhosis risk rises sharply above this cutoff.
Early intervention can still slow disease progression.