ALT and AST Levels in Fatty Liver: What Your Results Mean

TL;DR

• ALT and AST are liver enzymes that leak into the blood when liver cells are irritated. In fatty liver they’re often mildly raised, with ALT usually higher than AST.
• “Normal” ranges vary from lab to lab, and many are higher than what liver experts consider truly healthy (ALT about 29–33 U/L in men, 19–25 U/L in women). Normal enzymes don’t rule out fatty liver or scarring.
• The more useful number is often FIB-4, which combines your age, AST, ALT and platelets to estimate scarring risk. Below 1.3 is low risk; above 2.67 is high.

ALT and AST levels are often mildly elevated in fatty liver, but they can also be completely normal, even in people with significant scarring. So a raised ALT is a reason to look closer, and a normal one isn’t proof that your liver is fine.

These two enzymes are often the first hint that someone has MASLD (metabolic dysfunction-associated steatotic liver disease, formerly NAFLD; here’s what the new name means), often found on a routine blood test. This guide explains what ALT and AST measure, what counts as normal, what the AST/ALT ratio suggests, why doctors lean on the FIB-4 score, and what to ask at your next appointment.

What Are ALT and AST?

ALT (alanine aminotransferase) and AST (aspartate aminotransferase) are enzymes inside cells. When cells are damaged or stressed, some of these enzymes leak into the bloodstream, and blood levels rise. You’ll see them on a comprehensive metabolic panel, sometimes labeled SGPT (ALT) and SGOT (AST).

The key difference is where they come from:

• ALT is found mainly in the liver. That makes it the more specific marker of liver cell injury.
• AST is found in the liver and elsewhere, including heart muscle, skeletal muscle, kidney and brain.

That’s why, according to the American College of Gastroenterology (ACG), an AST rise without an ALT rise points more toward heart or muscle problems than the liver.

One important limit: ALT and AST measure ongoing irritation of liver cells. They don’t measure how much fat is in the liver, and they don’t measure scarring. They can’t tell you how well your liver is working, either. Other tests do that.

What Is a Normal ALT and AST Level?

There’s no single normal range. Each lab sets its own, and labs define their healthy reference groups differently, often without accounting for things like body weight. The ACG guideline cites one study in which 67 labs in a single US state used ALT upper limits anywhere from 31 to 72 U/L. That’s why the numbers on your report may differ from someone else’s.

Source	ALT	AST
MedlinePlus (NIH) example lab range	4–36 U/L	8–33 U/L
ACG “true healthy normal” ALT	29–33 U/L (men), 19–25 U/L (women)	Not specified
AASLD threshold suggesting chronic liver injury	Above 30 U/L, repeatedly or for 6–12 months or more	Above 30 U/L, same pattern
Your lab report	Check the range printed next to your result	Same

U/L (units per liter) and IU/L are used interchangeably on lab reports.

A few patterns worth knowing, from the ACG guideline:

• Many labs’ upper limits are higher than the healthy ranges above, so a result flagged “normal” may still be above what liver experts consider truly healthy. The AASLD makes the same point.
• ALT is naturally higher in men than in women.
• ALT rises with body weight. There’s a roughly linear relationship between ALT and BMI.
• An elevated ALT is linked to higher liver-related mortality, even in people without obvious risk factors, which is why persistently raised levels deserve follow-up.

If your ALT is 40 U/L, one lab might flag it and another might not. What matters more is the pattern over time and what else is going on: your weight, blood sugar, alcohol intake and the other tests below.

How High Are ALT and AST in Fatty Liver?

In fatty liver, when enzymes are raised, the rise is usually mild. A review in American Family Physician notes that people with fatty liver tend to have an AST/ALT ratio below 0.8, especially early, meaning ALT is the higher of the two.

But the more important point is that liver enzymes are often normal in fatty liver. The same review says so directly, and the ACG guideline notes that many people with fatty liver seen on imaging have normal liver chemistries. When enzymes are abnormal, the ACG says it signals a higher likelihood of MASH (the inflamed form), with or without scarring, and warrants evaluation.

Large rises, many times the upper limit of normal, are not the usual fatty liver picture. The ACG lists causes such as acute viral hepatitis, acetaminophen (Tylenol) toxicity and reduced blood flow to the liver, which need prompt medical attention.

Can You Have Fatty Liver With Normal Liver Enzymes?

Yes. This is one of the most important things to understand about liver labs:

• The ACG guideline states plainly that a normal ALT level may not exclude significant liver disease.
• The AASLD notes that AST can be normal in people with diabetes, MASH and advanced fibrosis.

So “my enzymes are normal” is not the same as “my liver is healthy,” especially if you have type 2 diabetes, obesity or several metabolic risk factors. That’s the gap FIB-4 and FibroScan are designed to fill.

What Does the AST/ALT Ratio Mean?

Dividing AST by ALT gives a ratio that can hint at the cause and stage of liver disease. It’s a clue, not a diagnosis.

AST/ALT ratio	What it can suggest
Below about 0.8–1 (ALT higher)	Typical of fatty liver, especially early
Rising toward or above 1	In fatty liver, can suggest progression to scarring
2 or higher	Classically linked to alcohol-related liver disease; AST and ALT rarely exceed 300 U/L in that setting
3 or higher	Makes alcohol-related liver disease even more likely
AST raised, ALT normal	Think beyond the liver: muscle or heart

The alcohol pattern comes from the ACG guideline, which explains that it largely reflects lower ALT activity in people with alcohol-related liver disease. The fatty liver pattern comes from the American Family Physician review, which notes that as the disease progresses to MASH with fibrosis, the ratio increases. That’s part of why AST and ALT both feed into the FIB-4 score. If your ratio is creeping up, ask about it, and read our guide on whether alcohol is safe with fatty liver.

What Else Can Raise ALT and AST?

Fatty liver is a very common reason for mildly raised enzymes, but it’s not the only one. The ACG guideline recommends checking for other causes, including:

• Alcohol, on its own or on top of fatty liver
• Viral hepatitis B and C
• Medications and supplements, both prescription and over-the-counter
• Hereditary hemochromatosis (iron overload)
• Autoimmune hepatitis
• Wilson disease and alpha-1 antitrypsin deficiency (less common inherited conditions)
• Celiac disease, which can cause modest enzyme rises
• Thyroid disorders, both underactive and overactive
• Muscle injury or strenuous exercise, which mainly raise AST

That last one catches people out. A hard gym session or long run shortly before a blood test can push AST up, so tell your doctor if you had one.

FIB-4: The Score That Uses Your ALT and AST

Because enzymes alone can’t tell you about scarring, the AASLD recommends a simple calculation called FIB-4 as the first step in assessing fibrosis risk. It uses four numbers you probably already have:

FIB-4 = (Age × AST) ÷ (Platelet count × √ALT)

Age is in years, AST and ALT in U/L, and platelets in 10⁹/L (the same number as “thousands per microliter” on most US reports).

FIB-4 result	Risk of advanced fibrosis (AASLD)	Usual next step
Below 1.3	Low	Manage in primary care; recheck periodically
1.3–2.67	Intermediate	A second test, usually FibroScan or a blood test called ELF
Above 2.67	High	Referral to a gastroenterologist or hepatologist should be considered

Two caveats from the AASLD: FIB-4 has low accuracy under age 35, and over age 65 a cutoff of 2.0 should be used instead of 1.3, because age alone pushes the score up. You may also see older cutoffs of 1.45 and 3.25 on some calculators.

Here’s how it plays out with example numbers:

Example	Age	AST	ALT	Platelets	FIB-4	What it shows
A	52	30	62	230	0.86	ALT is high, but scarring risk is low
B	58	42	48	190	1.85	Intermediate: a FibroScan is the usual next step
C	67	45	30	140	3.93	ALT looks normal, yet risk is high

Example C is the important one. Someone could be told their ALT is fine and still have a high-risk FIB-4. That’s why you should ask for the score, not just the enzymes.

What a FibroScan adds

If FIB-4 isn’t low, the next step is often a FibroScan (vibration-controlled transient elastography), a quick ultrasound-style test that measures liver stiffness in kilopascals (kPa). Per the AASLD, under 8 kPa can rule out advanced fibrosis, 8–12 kPa is a gray zone, over 12 kPa suggests advanced fibrosis is likely, and 20 kPa or more is associated with cirrhosis.

Do ALT Levels Go Down When Fatty Liver Improves?

Often, yes. As liver fat and inflammation come down, ALT usually follows. The AASLD notes that ALT normalization can predict resolution of MASH in response to lifestyle changes and several treatments.

Keep expectations realistic, though:

• ALT fluctuates. A single reading can bounce with recent exercise, alcohol, illness or medications. Trends over several tests matter more than one result.
• Falling ALT doesn’t prove scarring is improving. Fibrosis is tracked with FIB-4 and FibroScan over longer periods. The AASLD suggests rechecking FIB-4 every 1–2 years if you have prediabetes, type 2 diabetes or two or more metabolic risk factors, and every 2–3 years otherwise.
• The same levers help both. Weight loss is the main one: the 2024 European guideline aims for at least 5% loss to reduce liver fat, 7–10% to improve inflammation and 10% or more to improve fibrosis. Our guide on how to reverse fatty liver covers the full plan, and the fatty liver diet covers what to eat.

Small daily choices show up in these numbers over time. An app like Liverly can score each meal so you can see which habits, like sugary drinks or frequent takeout, are worth changing first.

Before Your Next Blood Test

A few practical steps make your results easier to interpret:

1. Skip unusually hard workouts right before the test, or tell your doctor if you did one.
2. Avoid alcohol in the days before the test if you can, and be honest about your usual intake.
3. Bring a list of everything you take, including supplements, herbal products and over-the-counter pain relievers.
4. Ask for copies of your results with the lab’s reference ranges, so you can track trends yourself.

What to Ask Your Doctor

Take these questions to your appointment:

• What were my ALT, AST and platelet count, and what is my FIB-4 score?
• Is my ALT above the “healthy” range even if the lab didn’t flag it?
• Have other causes been ruled out, such as hepatitis B and C, iron overload, medications or thyroid problems?
• Do I need a FibroScan or another second test?
• What is my estimated fibrosis stage, and does it change what I should do about alcohol?
• How much weight loss should I aim for, and when should we recheck?
• Should I see a hepatologist?

If you’ve been diagnosed with cirrhosis, some of this changes, including how you should eat. See our cirrhosis diet guide.

The Bottom Line

ALT and AST are useful warning lights, but they’re not a full picture of your liver. In fatty liver they’re often mildly raised, with ALT higher than AST, and just as often they’re normal. Lab ranges vary, and many sit above what experts consider truly healthy. Normal enzymes don’t rule out fatty liver or scarring, which is why the FIB-4 score, and a FibroScan when needed, matter more for judging risk. Ask for your FIB-4, understand your trend, and use the result to guide how hard you push on weight, diet, activity and alcohol.

Sources

• Kwo et al. ACG Clinical Guideline: Evaluation of Abnormal Liver Chemistries (American Journal of Gastroenterology 2017)
• AASLD Practice Guidance on the clinical assessment and management of nonalcoholic fatty liver disease (Rinella et al., Hepatology 2023)
• MedlinePlus: Alanine transaminase (ALT) blood test
• MedlinePlus: Aspartate aminotransferase (AST) blood test
• Nonalcoholic Fatty Liver Disease: Common Questions and Answers on Diagnosis and Management (American Family Physician 2020)

This article is for informational purposes only and is not medical advice. Talk to your doctor or hepatologist about your specific situation.