- Liver enzymes (ALT, AST) can be completely normal in fatty liver, even with scarring.
- The key question is not “is there fat?” but “is there scarring (fibrosis)?”
- A FIB-4 score under 1.3 means advanced scarring is unlikely; above 2.67 means it is likely and needs specialist follow-up.
- If FIB-4 is in between, a FibroScan helps: a reading under 8 kPa is reassuring.
You may have been told you have a “fatty liver” after an ultrasound, or that your liver numbers are “a bit high”. What happens next can be confusing, because there are several tests and each answers a different question. Fat in the liver on its own is common and usually not dangerous. What predicts serious liver problems down the line is fibrosis, the scar tissue that can build up over years. The whole testing pathway is designed to find the minority of people who have significant scarring, without sending everyone for a biopsy.
This article uses the current names: MASLD (metabolic dysfunction-associated steatotic liver disease, formerly NAFLD) and MASH (formerly NASH). For the basics, see Fatty Liver (MASLD) Explained.
What each test tells you
| Test | What it measures | Good to know |
|---|---|---|
| ALT and AST | Enzymes that leak from injured liver cells | Often normal in fatty liver. A normal result does not rule out fat or scarring. |
| Ultrasound | Fat, as a “bright” liver | Widely available and cheap, but can miss mild fat and cannot measure scarring. |
| FIB-4 | A scarring risk score from age, AST, ALT and platelets | Free, from routine blood tests. The recommended first step. |
| FibroScan (elastography) | Liver stiffness in kPa; the CAP reading estimates fat | Quick, painless, like an ultrasound. The usual second step. |
| ELF blood test | Markers of scar tissue turnover | An alternative second step where elastography is not available. |
| MRI | Precise liver fat (PDFF) and stiffness (MR elastography) | Accurate but costly; mainly used in specialist care and research. |
| Liver biopsy | A tiny tissue sample examined under a microscope | Still the reference standard, but now needed only in selected cases. |
Why normal liver enzymes can mislead
ALT is the liver number most people see on a routine blood panel. It rises when liver cells are being injured, so a raised ALT is a useful clue. But many people with fatty liver, including some with MASH and fibrosis, have ALT in the normal range. The “normal” range printed on many lab reports is also set higher than liver specialists consider healthy. As scarring advances, ALT may even fall, while AST rises relative to ALT. This is why guidelines advise against using enzymes alone to decide who is at risk, and why they built the FIB-4 score instead.
FIB-4: the first step
FIB-4 was first developed in people with hepatitis C and HIV, then validated in fatty liver. It combines four things you probably already have on a recent blood test: your age, AST, ALT and platelet count. Scarring pushes AST up relative to ALT and lowers platelets, and risk rises with age.
The formula: FIB-4 = (age × AST) ÷ (platelets × √ALT), with AST and ALT in U/L and platelets in 10⁹/L. Example: a 55-year-old with AST 40, ALT 45 and platelets 220 has (55 × 40) ÷ (220 × 6.7) = 1.49, just into the in-between zone. Your doctor or many online medical calculators can work it out for you.
FIB-4 cut-offs for advanced scarring in fatty liver
Shah et al., Clin Gastroenterol Hepatol 2009; AASLD Practice Guidance, Hepatology 2023. The marker shows the example above. For people aged 65 and over, a lower cut-off of 2.0 is often used to reduce false alarms (McPherson et al., Am J Gastroenterol 2017); FIB-4 is less reliable under age 35.
A low FIB-4 is very good at ruling out advanced scarring. Most people land here, and they can usually repeat the test every one to three years while working on lifestyle changes. A high score does not prove scarring, but it means you should see a liver specialist. An in-between score needs a second test.
FibroScan: the second step
Vibration-controlled transient elastography, best known by the brand name FibroScan, sends a gentle pulse through the liver and measures how fast it travels. Stiffer, more scarred livers carry the wave faster. The result is liver stiffness in kilopascals (kPa). The test takes about 10 minutes, feels like a light tap on the skin, and is best done after a few hours of fasting.
FibroScan liver stiffness
AASLD Practice Guidance, Hepatology 2023; EASL-EASD-EASO guideline, J Hepatol 2024. The marker shows an example low-risk result.
The same machine often reports a CAP score in dB/m, which estimates liver fat. CAP is useful for tracking fat, but the stiffness number is the one that guides decisions. Readings can be falsely high after a meal, with active inflammation or heavy drinking, or with heart failure. Where FibroScan is not available, the ELF blood test is an alternative second step; high scores suggest more scarring.
The step-by-step pathway
How guidelines recommend checking for scarring
Simplified from the AASLD 2023 and EASL-EASD-EASO 2024 guidance and the AGA clinical care pathway (Kanwal et al., Gastroenterology 2021). Local pathways vary.
When is a biopsy needed?
A liver biopsy removes a thin core of tissue with a needle, usually under local anesthetic. It is the only test that shows inflammation and cell injury directly, but it carries a small risk of bleeding and samples only a tiny part of the liver. Today it is mainly used when non-invasive tests disagree or are unclear, when another liver disease is suspected, or before some treatments and clinical trials.
See your doctor promptly if tests suggest high risk, or if you notice yellow eyes, a swelling belly, black stools or confusion. People with advanced scarring need regular checks for liver cancer and for enlarged veins that can bleed, and some medicines need dose changes. Decisions about treatment are individual, so talk to your doctor.
MythMy ultrasound says “fatty liver”, so I need a biopsy to know how bad it is.
FactMost people never need a biopsy. A FIB-4 score, followed by a FibroScan if needed, sorts most people into low or high risk.
Common questions
My ultrasound shows fatty liver but my blood tests are normal. Is that possible?
Yes, and it is very common. Ask whether your FIB-4 has been calculated, since that, not ALT, tells you your risk of scarring.
How often should I repeat FIB-4?
If it is low, guidelines suggest every one to three years, and more often if you have type 2 diabetes or several risk factors.
Can my FIB-4 or FibroScan improve?
Yes. Liver fat and stiffness can fall with weight loss, exercise and better blood sugar control. See Can Fatty Liver Be Reversed?
Is FIB-4 used in people with diabetes?
Yes. Diabetes and liver societies recommend it for adults with type 2 diabetes or prediabetes, who have a higher chance of scarring. See Type 2 Diabetes Risk Factors.
- Normal liver enzymes do not rule out fatty liver or scarring.
- FIB-4 uses age, AST, ALT and platelets: under 1.3 is low risk, above 2.67 is high risk.
- In between? A FibroScan under 8 kPa is reassuring; 8 kPa or more needs specialist review.
- Biopsy is now reserved for unclear cases. Symptoms are not a reliable guide; see fatty liver symptoms.
- Next: Can Fatty Liver Be Reversed? What the Evidence Shows.
Sources
- Rinella ME, Neuschwander-Tetri BA, Siddiqui MS, et al. AASLD Practice Guidance on the clinical assessment and management of nonalcoholic fatty liver disease. Hepatology. 2023;77(5):1797–1835.
- European Association for the Study of the Liver (EASL), European Association for the Study of Diabetes (EASD), European Association for the Study of Obesity (EASO). EASL-EASD-EASO Clinical Practice Guidelines on the management of metabolic dysfunction-associated steatotic liver disease (MASLD). J Hepatol. 2024;81(3):492–542.
- Sterling RK, Lissen E, Clumeck N, et al. Development of a simple noninvasive index to predict significant fibrosis in patients with HIV/HCV coinfection. Hepatology. 2006;43(6):1317–1325.
- Shah AG, Lydecker A, Murray K, et al. Comparison of noninvasive markers of fibrosis in patients with nonalcoholic fatty liver disease. Clin Gastroenterol Hepatol. 2009;7(10):1104–1112.
- McPherson S, Hardy T, Dufour JF, et al. Age as a confounding factor for the accurate non-invasive diagnosis of advanced NAFLD fibrosis. Am J Gastroenterol. 2017;112(5):740–751.
- Kanwal F, Shubrook JH, Adams LA, et al. Clinical care pathway for the risk stratification and management of patients with nonalcoholic fatty liver disease. Gastroenterology. 2021;161(5):1657–1669.
- Rinella ME, Lazarus JV, Ratziu V, et al. A multisociety Delphi consensus statement on new fatty liver disease nomenclature. Hepatology. 2023;78(6):1966–1986.
This article is for general education and is not a substitute for advice from your own doctor or healthcare team.