On This Page – Quick Medical Summary
Can you calculate your own FIB-4 score from lab results?
Yes. If your lab report lists AST, ALT and platelets, you can calculate a FIB-4 score in about a minute. It estimates the chance of advanced liver fibrosis (scarring); it does not diagnose anything.
- Yellow skin or eyes, or feeling acutely unwell: wrong tool right now. See next steps for high liver enzymes and arrange prompt in-person care.
- Mildly raised enzymes, a fatty liver finding or a score in hand: keep reading; guidelines use FIB-4 as the first screen.
ℹ️ Medical Disclaimer: This article explains a screening calculation for education. It does not diagnose liver disease, choose tests, or advise on treatment or medication; a primary-care clinician or hepatologist (liver specialist) must review your results.
What AST, ALT and platelets reveal about liver scarring
FIB-4 turns four routine numbers into one risk estimate.
What AST and ALT measure
AST and ALT are enzymes made mainly in the liver, per MedlinePlus’ liver function tests overview. Other conditions and medicines can change them, so see how the AST-to-ALT ratio is read.
Why platelet count matters
A low platelet count is common with advanced fibrosis, so platelets sit in the formula.
Why age is in the formula
Age multiplies straight into the score, so identical labs give a higher number at an older age.
🔬 How It Works: AST and age sit on top of the equation; platelets and the square root of ALT sit underneath, so a higher AST or a lower platelet count raises the score.
How to calculate FIB-4 step by step (with an example)
FIB-4 equals age times AST, divided by platelets times the square root of ALT.
The formula and the units to use
- Multiply age in years by AST (U/L).
- Multiply platelets (10⁹/L) by the square root of ALT (U/L).
- Divide step 1 by step 2.
It was first built in people with HIV and hepatitis C, per the original derivation study.
Worked example: age 52
Illustration, not a real patient: age 52, AST 48, ALT 52, platelets 210. Then 52 × 48 = 2,496; 210 × √52 (about 7.21) ≈ 1,514; and 2,496 ÷ 1,514 = 1.65, an indeterminate result.
The platelet unit mistake
Labs often print platelets as ×10³/µL, the same number as 10⁹/L. Typing 210,000 instead gives about 0.0016, a falsely tiny score.
What your FIB-4 number means: 1.3, 2.0 and 2.67
Guideline pathways sort FIB-4 into three ranges.
Low, indeterminate and high ranges
| FIB-4 result | What it suggests | Key clinical detail |
|---|---|---|
| Below 1.3 | Advanced fibrosis unlikely | Below 2.0 if 65 or older |
| 1.3 to 2.67 | Indeterminate | Cannot rule fibrosis in or out |
| Above 2.67 | Advanced fibrosis more likely | Needs confirmation |
Source: Labcorp and Northwell Health test notes; AGA pathway summary (March 2026).
Why some calculators show 1.45 and 3.25
Some calculators still use the original HIV and hepatitis C cutoffs of 1.45 and 3.25. Fatty liver pathways use 1.3 and 2.67, after FIB-4 was studied in fatty liver disease.
The age-65 cutoff
For adults 65 and older, the AGA pathway uses 2.0 instead of 1.3. Sources word the boundary differently; if you are exactly 65, ask which applies.
✅ Patient Action: Ask a primary-care clinician or hepatologist: “Which FIB-4 cutoff applies at my age?”
How accurate is the FIB-4 score?
FIB-4 is a screening filter, so accuracy depends on who is tested.
What the original study found
In the original study, below 1.45 gave a 90% negative predictive value; above 3.25 gave a 65% positive predictive value.
How it performs in fatty liver disease
The AGA pathway summary reports negative predictive values of 90% or higher below 1.3; Labcorp cites 83% in fatty liver studies.
Where real-world data disagrees
📊 Clinical Data Point: Among 3,741 US adults at risk for fatty liver disease, 10% of the 2,776 (74.2%) classed low risk by FIB-4 were not low risk on liver stiffness testing; of 86 classed high risk, 79.1% were not high risk. Source: NHANES 2017–2020 analysis in Clinical Gastroenterology and Hepatology.
So FIB-4 decides who gets a second test, not who has fibrosis.
What to do after your FIB-4 result
Your next step depends on your score’s range.
If your score is low
Advanced fibrosis is unlikely; the AGA pathway describes retesting every one to two years in primary care (other guidance differs). It also stresses cardiometabolic risk factors; our BMI calculator tracks one.
If your score is indeterminate
A second test follows: FibroScan (vibration-controlled transient elastography) or, where unavailable, the ELF blood test. Per the AGA summary, below 8 kPa is low risk and 8 kPa or higher prompts hepatology referral; see also normal ALT with liver damage and FIB-4.
If your score is high
Above 2.67, pathways typically refer to a hepatologist for confirmatory testing; it is an estimate, not a diagnosis.
✅ Patient Action: Ask a hepatologist or primary-care clinician: “Do I need FibroScan or ELF testing, and when should I repeat FIB-4?”
When FIB-4 can mislead: age, illness and lab quirks
Anything that shifts your labs or age shifts the score.
Under 35 and over 65
AASLD educational material notes FIB-4 is less reliable under 35 and over 65. In one referral cohort aged 65 and older, a 1.3 cutoff had a 100% negative predictive value for liver stiffness of 10 kPa or more versus 83% at 2.0, per that cohort study.
Illness, alcohol and lab effects
Alcohol and other AST-raising exposures can inflate the score, and recent illness that changes AST, ALT or platelets can distort it, as can causes of a low platelet count.
⚠️ Clinical Warning: A screening score is a poor guide when you are acutely unwell or have yellow skin or eyes; seek prompt in-person evaluation instead.
FIB-4 calculator FAQs
1. How do you calculate FIB-4 from AST, ALT and platelets?
Multiply age by AST, then divide by platelets times the square root of ALT, using U/L and 10⁹/L.
2. What is a good FIB-4 score?
FIB-4 below 1.3 is low risk, or below 2.0 at 65 and older. A clinician should confirm what your result means.
3. What does a FIB-4 of 1.3 mean?
FIB-4 of 1.3 is the lower cutoff: below it advanced fibrosis is unlikely; at or above it, a second test usually follows.
4. What does a FIB-4 above 2.67 mean?
A FIB-4 above 2.67 is high risk and typically prompts hepatologist referral for confirmatory testing; it is not a diagnosis.
5. What FIB-4 cutoff applies over 65?
For adults 65 and older, the AGA pathway uses 2.0 as the lower FIB-4 cutoff; confirm the exact age boundary with your clinician.
6. What units go into the FIB-4 formula?
FIB-4 uses age in years, AST and ALT in U/L, and platelets in 10⁹/L, the same number as ×10³/µL.
7. How accurate is FIB-4?
FIB-4 misclassifies some people: in a US study, 10% of low-risk results were not low risk on stiffness testing.
8. What test follows an indeterminate FIB-4?
After an indeterminate FIB-4, FibroScan-type elastography or an ELF blood test usually follows. Ask your clinician which applies.
9. Can alcohol or illness skew FIB-4?
Yes. Alcohol can raise AST and inflate FIB-4, and illness that changes AST, ALT or platelets can distort it.
10. Does a low FIB-4 rule out liver disease?
No. Low FIB-4 makes advanced fibrosis unlikely but can miss cases, so it does not rule out liver disease.
11. How often should FIB-4 be repeated?
FIB-4 repeat intervals vary; the AGA pathway describes one to two years after a low score. Ask your clinician.
Your next step after calculating FIB-4
FIB-4 sorts you toward reassurance, a second test or a specialist. Bring your age, AST, ALT, platelets and result to a primary-care clinician or hepatologist, and ask which cutoff applies at your age.
About this content
How this article was put together: researched from recognised health sources, drafted with the help of AI tools, and edited by hand, with sources linked throughout.
Sameer Patel is the founder and editor of My Medicine Advisor. He is not a doctor or medical professional — before starting this site he worked in banking,…
Medical disclaimer
The content on MyMedicineAdvisor is provided for general informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Health information on this website should not be used to diagnose, treat, cure, or prevent any condition without guidance from a qualified healthcare professional. Always seek the advice of your doctor, physician, or another licensed healthcare provider with any questions you may have regarding a medical condition, symptoms, medications, or treatment decisions.
