Liver Function Test Results Explained: ALT, AST, ALP and More

TL;DR

• A “liver function test” is really a panel. ALT and AST show liver cell irritation, ALP, GGT and bilirubin show bile flow, and albumin and INR show how well the liver is working.
• One slightly abnormal number rarely means much on its own. The pattern, how far above the upper limit it is, and the trend over time matter most.
• In fatty liver the panel is often normal or only mildly off, so ask for your FIB-4 score too. It uses ALT, AST, platelets and age to estimate scarring risk.

Liver function tests are a group of blood tests that show whether liver cells are being irritated, whether bile is flowing normally, and how well the liver is doing its job. A single result slightly outside the range is common and often harmless; what matters is the pattern across the tests and how it changes over time.

This guide walks through each test on a typical liver panel, what the numbers mean, the patterns doctors look for, and which results matter most if you have, or might have, fatty liver.

What Is in a Liver Function Test?

A liver panel (also called a hepatic function panel or LFTs) usually includes:

• ALT and AST, enzymes that leak out of irritated liver cells
• ALP and GGT, enzymes linked to the bile ducts (ALP also comes from bone)
• Bilirubin, total and sometimes direct, a yellow waste product of old red blood cells that the liver clears
• Albumin and total protein, proteins mostly made by the liver
• Prothrombin time (PT) and INR, which measure how quickly blood clots

The American College of Gastroenterology (ACG) makes a useful point about the name: most of these tests measure injury, not function, so it prefers “liver tests” or “liver chemistries.” Albumin and prothrombin time are the clearest markers of how well the liver is working. The standard comprehensive metabolic panel includes ALT, AST, ALP, bilirubin and albumin; GGT and PT are often added separately.

One more number belongs on your radar even though it comes from a different test: your platelet count, from a complete blood count. It’s one of the four inputs to FIB-4.

Liver Function Test Results: What Each Test Means

Here’s what each test measures, with the example adult ranges MedlinePlus gives. Your lab’s ranges may differ, and the range printed on your report is the one to use.

Test	What it measures	Typical range (example)	What high or low can mean
ALT (SGPT)	Enzyme found mainly in the liver; the most liver-specific marker of liver cell injury	4–36 U/L	High: fatty liver, alcohol, viral hepatitis, medicines and other liver injury. See our ALT guide
AST (SGOT)	Enzyme in the liver plus heart, muscle, kidney and brain	8–33 U/L	High: liver injury, but also muscle injury or hard exercise. See our AST guide
ALP	Enzyme in the liver’s bile channels and in bone (also placenta, intestine, kidney)	40–129 IU/L	High: slowed bile flow, bone disease, growth in children, pregnancy. Low: can occur with malnutrition, zinc deficiency or an underactive thyroid
GGT	Enzyme mainly in the liver and bile ducts	5–40 U/L	High: alcohol, fatty liver, bile-flow problems, some medicines. Confirms that a high ALP is from the liver. See our GGT guide
Total bilirubin	Waste pigment from old red blood cells, cleared by the liver	0.1–1.2 mg/dL	High: Gilbert syndrome, red blood cell breakdown, liver disease, blocked bile ducts
Direct (conjugated) bilirubin	Bilirubin the liver has already processed	Below 0.3 mg/dL	High: liver cell disease or bile-duct obstruction
Albumin	A blood protein made only by the liver	3.4–5.4 g/dL	Low: longer-standing liver disease, kidney disease, poor nutrition or any serious illness
Total protein	Albumin plus other proteins (globulins)	6.5–8.1 g/dL	Low: liver disease, malnutrition, protein loss. High: chronic inflammation or infection, some blood cancers
PT / INR	How long blood takes to clot, which depends on proteins the liver makes	PT 11–13.5 seconds; INR 0.8–1.1	Longer: severe liver disease, low vitamin K, blood thinners such as warfarin
Platelets (blood count)	Cells that help blood clot	150–400 × 10⁹/L	Low: many causes; in liver disease, a sign of raised pressure in the liver’s blood supply as scarring advances

U/L and IU/L are interchangeable. Outside the US, bilirubin is often reported in µmol/L (MedlinePlus gives 1.71–20.5 µmol/L for total bilirubin) and albumin in g/L (34–54 g/L).

For ALT, many labs’ upper limits are higher than what liver experts consider truly healthy. The ACG puts a healthy ALT at about 29–33 U/L for men and 19–25 U/L for women, and the AASLD notes that ALT or AST above 30 U/L that stays up for 6–12 months may point to chronic liver injury.

What Does My Number Mean?

For ALT and AST, how far above the upper limit you are matters more than the exact number. Divide your result by the upper limit on your report: an ALT of 90 U/L with an upper limit of 40 U/L is about 2.3 times the upper limit. The ACG uses these bands:

Your ALT or AST	ACG term	What it can mean
Up to the upper limit	Normal for your lab	Reassuring, but it doesn’t rule out fatty liver or scarring
Up to 2× the upper limit	Borderline	Seen in many liver and non-liver conditions, including fatty liver, alcohol and medicines. Usually repeated
2–5×	Mild	Same wide list of causes; your doctor will look for the reason, often starting with hepatitis B and C, alcohol and fatty liver
5–15×	Moderate	Needs immediate medical evaluation, per the ACG
More than 15×	Severe	Needs immediate evaluation. Causes include acute viral hepatitis, medicine or toxin injury and reduced blood flow to the liver
Above 10,000 U/L	Massive	Usually reduced blood flow (“shock liver”) or drug or toxin injury, such as acetaminophen overdose

Lab reference ranges differ, so the range on your own report wins. And no single result is a diagnosis: your doctor will look at the trend and your other results. The ACG recommends repeating an abnormal result, or doing a clarifying test, before starting a full workup.

Hepatocellular or Cholestatic? Reading the Pattern

Doctors sort abnormal liver tests into patterns, which narrow down the cause. The ACG describes four:

• Hepatocellular: ALT and AST are raised out of proportion to ALP. This points to injury inside liver cells, as in fatty liver, viral hepatitis or medicine injury.
• Cholestatic: ALP is raised out of proportion to ALT and AST. This points to a bile-flow problem, such as a blocked duct or an inflammatory bile-duct disease.
• Mixed: both are raised.
• Isolated high bilirubin: bilirubin is up but the enzymes and ALP are normal.

To make this less of a judgment call, doctors can calculate the R ratio: (ALT ÷ ALT upper limit) ÷ (ALP ÷ ALP upper limit). Per the ACG, above 5 is hepatocellular, below 2 is cholestatic, and 2–5 is mixed.

Two examples, assuming upper limits of 40 U/L for ALT and 120 IU/L for ALP:

• ALT 240 and ALP 110: (240 ÷ 40) ÷ (110 ÷ 120) = 6 ÷ 0.92 ≈ 6.5, hepatocellular
• ALT 60 and ALP 360: (60 ÷ 40) ÷ (360 ÷ 120) = 1.5 ÷ 3 = 0.5, cholestatic

Fatty liver usually shows a mild hepatocellular pattern, with ALT higher than AST. When AST catches up with or passes ALT, that can point to more advanced scarring or alcohol, which our guide to the AST/ALT ratio explains.

What Do Albumin, Bilirubin and INR Tell You?

Albumin and INR are the closest the panel gets to measuring how well the liver works, and bilirubin shows how well it clears a waste product.

Albumin is made only by the liver and has a half-life of about 3 weeks in the blood. So, as the ACG explains, a low albumin usually reflects liver disease that has been going on for more than 3 weeks. It isn’t specific, though: kidney disease, poor nutrition and any significant illness can lower it too.

Prothrombin time and INR respond much faster. The ACG notes that PT can lengthen within 24 hours in severe liver injury, which is why it’s checked when someone has acute hepatitis. But it isn’t an early warning sign: the ACG notes that liver-related lengthening doesn’t typically happen until clotting factors fall below 10% of normal. Vitamin K deficiency and blood thinners such as warfarin also lengthen it.

Bilirubin comes in two forms. Indirect (unconjugated) bilirubin hasn’t been processed by the liver yet; direct (conjugated) bilirubin has. A high direct bilirubin suggests liver cell disease or a bile-duct blockage. A high indirect bilirubin with otherwise normal tests is most often Gilbert syndrome, which the ACG says affects 3–7% of the US population. In Gilbert syndrome bilirubin is usually below 3 mg/dL, and once medicines and red blood cell breakdown are ruled out, no further testing is routinely needed.

Which Liver Tests Matter Most for Fatty Liver?

If you have, or might have, MASLD (metabolic dysfunction-associated steatotic liver disease, formerly NAFLD), focus on these:

1. ALT and AST. Often mildly raised in fatty liver, with ALT higher than AST, but just as often normal. The AASLD notes they are frequently normal even in advanced disease, so a normal result doesn’t rule out scarring. Our pillar guide to ALT and AST levels in fatty liver covers this in depth.
2. Platelets and FIB-4. Your age, AST, ALT and platelet count combine into the FIB-4 score, the AASLD’s recommended first step for judging scarring risk. Below 1.3 is low risk and above 2.67 is high. Work yours out with our FIB-4 calculator.
3. GGT. Can be raised in fatty liver and is very sensitive to alcohol, though not specific.
4. FibroScan, if FIB-4 isn’t low. It measures liver stiffness directly. Our guide to FibroScan results explains the numbers.

Albumin, bilirubin and INR tend to change later, so they matter most when liver disease is advanced.

What Happens After an Abnormal Liver Test?

The ACG guideline lays out a step-by-step approach. For mildly raised enzymes, your doctor will usually:

• Repeat the test to confirm the result is really abnormal.
• Take a careful history: alcohol, prescription and over-the-counter medicines, supplements and herbal products.
• Test for common causes, including hepatitis B and C, iron overload (hemochromatosis) and fatty liver risk factors, and less common ones such as autoimmune hepatitis, Wilson disease and alpha-1 antitrypsin deficiency.
• Order an ultrasound if ALP is high or fatty liver is suspected, to look at the liver and bile ducts.
• Calculate FIB-4 if fatty liver is likely, as the AASLD recommends.

Larger rises, five times the upper limit or more, are evaluated right away, and acute hepatitis with a prolonged clotting time or confusion calls for immediate referral to a liver specialist.

Before Your Next Liver Panel

1. Follow your lab’s instructions on fasting. ALT and AST need no special preparation, but some liver panels ask you to fast, sometimes for 10–12 hours.
2. Skip unusually hard workouts right before the test, since muscle strain raises AST.
3. Avoid alcohol before the test, and be honest about your usual intake.
4. Bring a list of everything you take, including supplements. Don’t stop a prescribed medicine unless your provider tells you to.
5. Ask for copies of your results with the reference ranges, so you can track the trend yourself.

The Bottom Line

A liver function test is a panel, not a single verdict. ALT and AST show liver cell irritation, ALP, GGT and bilirubin show how bile is flowing, and albumin and INR show how well the liver is working. Read each result against your own lab’s range, look at how far above the upper limit it is and which pattern it fits, and pay attention to the trend. If fatty liver is the concern, ask for your FIB-4 score as well, because a normal panel doesn’t rule out scarring.

Sources

• Kwo et al. ACG Clinical Guideline: Evaluation of Abnormal Liver Chemistries (American Journal of Gastroenterology 2017)
• MedlinePlus (US National Library of Medicine): Liver Function Tests
• MedlinePlus Medical Encyclopedia reference ranges: ALT, AST, ALP, GGT, bilirubin, albumin, total protein, prothrombin time, platelet count
• AASLD Practice Guidance on the clinical assessment and management of nonalcoholic fatty liver disease (Rinella et al., Hepatology 2023)

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