π« FIB-4 Liver Fibrosis Calculator
Four routine labs, one fibrosis risk number.
For informational purposes only, not medical advice. Consult a healthcare professional.
FIB-4 estimates advanced liver fibrosis risk from four routine numbers: age Γ AST / (platelets Γ βALT). Age 50, AST 40, ALT 30, platelets 200 gives 1.83, indeterminate (low is under 1.3, high over 2.67). Enter your labs for your band and next step.
How to Use This Calculator
FIB-4 was developed for hepatitis C and validated across NAFLD/MASLD, alcohol-related disease, and hepatitis B. It uses labs you already have.
Enter age and the AST and ALT in U/L from the metabolic panel. Use the most recent values, drawn when you were not acutely ill.
Enter platelets in x10^9/L (same as K/Β΅L). Low platelets reflect portal hypertension and splenic sequestration as fibrosis advances.
Read the index and band. Low risk usually just needs repeat testing later; indeterminate needs elastography; high risk needs hepatology.
The Formula
Each term earns its place: age because fibrosis accumulates over time; AST rising relative to ALT because advanced fibrosis flips the AST/ALT ratio above 1; platelets falling because portal hypertension traps them in the spleen. The square root on ALT dampens its influence so acute hepatitis spikes do not dominate. The index is a risk score, not a measurement: it was calibrated against liver biopsy, and its cutoffs were chosen for clinical jobs, under 1.3 to rule out advanced fibrosis (high negative predictive value) and over 2.67 to rule it in.
Worked Example
Age 50, AST 40, ALT 30, platelets 200: FIB-4 = 50 Γ 40/(200 Γ β30) = 2000/(200 Γ 5.477) = 2000/1095.4 = 1.83, indeterminate. A cleaner low-risk case: age 40, AST 25, ALT 30, platelets 250: 40 Γ 25/(250 Γ 5.477) = 1000/1369.3 = 0.73, low risk. A high-risk case: age 65, AST 80, ALT 45, platelets 110: 65 Γ 80/(110 Γ 6.708) = 5200/737.9 = 7.05, high risk. I verified each against the formula. Notice how platelets dominate the high-risk case: 110 platelets with an AST/ALT ratio above 1 is the classic advanced-fibrosis lab signature.
Cutoffs and Next Steps
| FIB-4 | Band (under 65) | Next step |
|---|---|---|
| Under 1.3 | Low risk | Advanced fibrosis unlikely; repeat in 1-3 years if risk persists |
| 1.3 - 2.67 | Indeterminate | Elastography (FibroScan) or ELF test to clarify |
| Over 2.67 | High risk | Hepatology referral; evaluate for cirrhosis complications |
For age 65+, the low-risk cutoff rises to 2.0, because age inflates the score and the 1.3 line would flag too many healthy older adults. AASLD guidance uses FIB-4 as the first-line triage for NAFLD/MASLD: low risk stays in primary care with lifestyle management, indeterminate gets the second-line test, high risk goes to hepatology. The indeterminate zone is deliberately wide; about a third of patients land there, and elastography resolves most of them. For related metabolic numbers, our HOMA-IR calculator quantifies the insulin resistance driving most fatty liver, our hepatic steatosis index estimates fat in the liver itself, and our BMI calculator tracks the weight behind both.
When FIB-4 Misleads
Acute hepatitis spikes AST/ALT into the hundreds and inflates the score without reflecting fibrosis; wait for resolution and repeat. Thrombocytopenia from other causes (ITP, chemo) falsely raises it. Age over 65 needs the 2.0 cutoff, and even then specificity falls. FIB-4 is less validated under 35, where advanced fibrosis is rare and the score runs low anyway. It also cannot distinguish fibrosis stages within the high band: 3.0 and 8.0 are both "high risk" but different diseases. Treat it as triage, which is its designed job, not as a fibrosis meter.
What Lowers the Score Honestly
In MASLD, the interventions with biopsy-proven fibrosis benefit are weight loss (7-10% of body weight), Mediterranean-style eating, regular exercise, alcohol abstinence, and diabetes control. GLP-1 medications show promise for steatohepatitis. The score moves slowly: recheck yearly, not monthly, and judge the trend over years. Platelets recover slowly if at all once portal hypertension is established, so early action while the score is indeterminate counts the most.
FIB-4 in Primary Care Workflows
The best FIB-4 programs are automatic: the EHR computes it from existing labs for every patient with diabetes, obesity, or abnormal liver enzymes, flagging indeterminate and high scores for the clinician. This catches the silent majority of MASLD, since fatty liver rarely hurts until it is advanced. If your practice does not auto-compute, the manual version takes a minute with this calculator and belongs in the annual review of any patient with metabolic risk factors. The yield is real: studies of automated FIB-4 screening find advanced fibrosis in 5-10% of flagged patients who had no liver diagnosis.
Combining FIB-4 With Other Noninvasive Tests
Guidelines increasingly use sequential testing: FIB-4 first, then elastography or the ELF blood test for indeterminate scores, which together classify over 80% of patients without biopsy. The FAST score (FibroScan-AST) adds steatohepatitis detection for trial enrollment. No single noninvasive test replaces biopsy for borderline cases, but the sequence means biopsy is now reserved for genuine uncertainty rather than routine staging. If your FIB-4 is indeterminate, ask about the next test in your system's pathway rather than waiting a year to repeat the same score.
For informational purposes only, not medical advice. Consult a healthcare professional.
Frequently Asked Questions
What is a normal FIB-4 score?
Under 1.3 (under age 65) or under 2.0 (65+) is low risk for advanced fibrosis. There is no 'normal' single value; the score is interpreted against rule-out and rule-in cutoffs.
What FIB-4 score indicates cirrhosis?
Over 2.67 is high risk for advanced fibrosis including cirrhosis, but FIB-4 cannot diagnose cirrhosis by itself. Imaging, elastography, and clinical signs confirm it.
How accurate is FIB-4?
Good for triage: the low cutoff rules out advanced fibrosis with ~90%+ negative predictive value, and the high cutoff rules it in reasonably well. The indeterminate zone (1.3-2.67) needs a second test.
Can FIB-4 be high without liver disease?
Yes: acute hepatitis spikes transaminases, low platelets from other causes (ITP, chemotherapy), and older age all inflate it. Repeat after acute illness resolves and interpret in context.
How often should FIB-4 be repeated?
Yearly in MASLD/NAFLD under monitoring, or every 1-3 years in low-risk patients with ongoing risk factors. It moves slowly; monthly rechecks add noise, not information.
Does FIB-4 work for alcohol-related liver disease?
Yes, it is validated in alcohol-related disease as well as viral hepatitis and MASLD. Active heavy drinking can acutely raise transaminases, so interpret during abstinence when possible.
Why is the cutoff higher after 65?
Age is in the numerator, so scores drift up with age independent of fibrosis. The 2.0 cutoff for 65+ preserves the test's rule-out performance in older adults.
What is the difference between FIB-4 and FibroScan?
FIB-4 is a calculated blood-based triage score; FibroScan (transient elastography) physically measures liver stiffness. Guidelines use FIB-4 first, then elastography for indeterminate scores.
Can weight loss improve FIB-4?
Yes, through its components: weight loss lowers transaminases and can improve platelets as portal pressure eases. 7-10% weight loss has biopsy-proven benefits in steatohepatitis.
Should I worry about an indeterminate FIB-4?
It means 'needs a second test,' not 'disease present.' About a third of screened patients land there, and most are clarified as low risk by elastography. Arrange the follow-up rather than worrying.