Liver Function Tests (LFTs): What They Measure, Normal Ranges and Results
Updated: 4 days ago
Written and medically reviewed by Dr. Baraa Alnahhal, MD · Last reviewed: November 2026 · How we review
Quick Answer: What are liver function tests?
Liver function tests (LFTs) are blood tests that measure substances your liver makes or processes, including enzymes, proteins and bilirubin. A liver panel usually checks several of these from one blood sample. Levels that are too high or too low can point to liver inflammation, bile duct problems, medicine side effects or other liver diseases. [1]
What the research says
"Healthy" ALT is lower than many lab limits. An American College of Gastroenterology guideline states that a truly healthy normal ALT ranges from 29 to 33 IU/L in males and 19 to 25 IU/L in females, and higher levels should be assessed. (Kwo et al., The American Journal of Gastroenterology, 2017) [2]
Even "normal-high" enzymes carry risk. In 142,055 Korean adults followed for eight years, men with AST of 30 to 39 IU/L had 8 times the risk of dying from liver disease compared with levels under 20 IU/L. (Kim et al., BMJ, 2004) [3]
Key takeaways
Liver function tests are a simple blood draw that checks how your liver is working. [1]
A panel usually includes liver enzymes, proteins, bilirubin, LDH and prothrombin time. [1]
They are part of the routine comprehensive metabolic panel. [1]
Normal ranges vary by sex, body size and lab. [1]
Abnormal results guide more tests; they rarely diagnose a disease on their own. [1]
What do liver function tests measure?
Liver function tests measure different substances made by your liver. Together, they show how healthy your liver is and how well it is working. [1]
Test | What it shows |
Liver enzymes: ALP, ALT, AST and GGT | These rise when there is liver injury |
Total protein | Your liver makes protein; low levels may mean it is not working well |
Bilirubin | A waste product your liver puts into bile |
Lactate dehydrogenase (LDH) | An enzyme found in many tissues, including the liver |
Prothrombin time (PT) | How long blood takes to clot, using proteins the liver makes |
Sources: [1]
Several of these tests, including ALT, AST, ALP, bilirubin, albumin and total protein, are part of a routine blood panel called a comprehensive metabolic panel (CMP). [1]
Why are liver function tests done?
Your provider may order them to screen for hepatitis or other liver diseases, to check how a known liver disease is progressing or responding to treatment, or to watch for side effects of medicines known to affect the liver. [1]
Different values and ratios can tell your provider: [1]
Whether you have liver inflammation (hepatitis)
Whether the inflammation is alcohol-related or nonalcoholic (metabolic)
Whether the problem is in the liver itself or in the bile ducts
Whether liver function or bile flow is impaired, and by how much
Whether your medicines are affecting your liver
How are liver function tests done?
A healthcare provider draws a small amount of blood from a vein in your arm. They clean the site, may wrap a band around your arm, insert a small needle and fill a vial. It takes only a few minutes. [1]
The sample goes to a lab, and results can take a few hours to a few days. If you do not feel lightheaded, you can go home, eat, drink and take your usual medicines. [1]
What are normal liver function test ranges?
Normal ranges vary between sexes, body sizes and laboratories. On average, they are: [1]
Test | Average normal range |
Alanine transaminase (ALT) | 0 to 45 IU/L |
Aspartate transaminase (AST) | 0 to 35 IU/L |
Alkaline phosphatase (ALP) | 30 to 120 IU/L |
Gamma-glutamyltransferase (GGT) | 0 to 30 IU/L |
Bilirubin | 2 to 17 micromoles/L |
Prothrombin time (PT) | 10.9 to 12.5 seconds |
Albumin | 40 to 60 g/L |
Total proteins | 6.3 to 8.0 g/dL |
Sources: [1]
Reading these results takes skill, because providers often compare levels of different enzymes and proteins with each other. Your provider will walk you through your results. [1]
What do high AST and ALT mean?
High AST and ALT may mean liver injury, since these are the enzymes most often released into the blood when the liver is stressed. [1]
What can liver function tests help diagnose?
These blood tests often cannot diagnose a specific liver disease on their own, but they point your provider in the right direction and help rule out other causes. You may need imaging, a liver biopsy or blood tests for specific viruses. Possible diagnoses include: [1]
Fatty liver disease
Toxic hepatitis or autoimmune hepatitis
Viral hepatitis (A, B or C)
Hemochromatosis
Wilson's disease
Alpha-1 antitrypsin deficiency
Primary biliary cholangitis (PBC)
Cirrhosis
Liver cancer
Conclusion
Liver function tests are one of the simplest ways to check on your liver. A single blood sample gives your provider a lot of information about liver injury, bile flow and how well your liver makes proteins.
If your results are abnormal, ask which values were out of range and what follow-up tests your provider recommends.
Keep learning: Read our guide to fatty liver disease (MASLD) or learn about cirrhosis of the liver. For more background, see MedlinePlus on liver function tests.
FAQ
What are liver function tests?
They are blood tests that measure liver enzymes, proteins and bilirubin to check how well your liver is working. [1]
What is included in a liver panel?
Usually ALT, AST, ALP, GGT, total protein, albumin, bilirubin, LDH and prothrombin time. [1]
What is a normal ALT level?
On average, ALT ranges from 0 to 45 IU/L, though ranges vary by lab, sex and body size. [1]
What is a normal AST level?
On average, AST ranges from 0 to 35 IU/L. [1]
What do high liver enzymes mean?
High AST and ALT usually mean the liver is stressed or injured. [1]
What does it mean if AST is higher than ALT?
When AST is about twice as high as ALT, it points to alcohol-related liver injury. [1]
Do I need to fast for a liver function test?
Follow your provider's instructions; after the blood draw you can eat, drink and take your usual medicines. [1]
How long do liver function test results take?
Results can take a few hours to a few days, depending on the lab. [1]
Can liver function tests diagnose liver disease?
They point to a likely cause, but imaging, a biopsy or virus tests are often needed to confirm it. [1]
Why are liver function tests ordered with medicines?
They are used to watch for side effects of medicines known to affect the liver. [1]
Related Reading
Enzyme Markers: Blood Tests for Heart, Liver and Muscle Damage explains blood tests that detect heart, liver and muscle damage.
AST Blood Test (Aspartate Transferase): Normal Range and Results explains the AST liver enzyme blood test.
Acetaminophen Level Test: Checking for Tylenol Overdose explains the blood test used to diagnose and treat acetaminophen overdose.
Liver-Spleen Scan: Nuclear Imaging of Liver and Spleen Function explains the nuclear scan that shows liver and spleen function.
Antimitochondrial Antibody (AMA) Test for Primary Biliary Cholangitis explains the blood test that helps diagnose primary biliary cholangitis.
Fatty Liver Disease (MASLD): The Silent Liver Condition Linked to Weight, Diabetes, and Metabolism explains a common cause of abnormal liver tests.
Alcoholic Hepatitis: What Heavy Drinking Does to Your Liver, and Whether the Damage Can Be Reversed covers the liver injury linked to a high AST-to-ALT ratio.
Cirrhosis of the Liver: What It Is, How Permanent Scarring Damages Your Liver, and What Treatment Involves describes advanced liver scarring that liver tests help monitor.
Hemochromatosis: The Iron Overload Disease That Hides for Decades explains an inherited cause of abnormal liver tests.
Wilson's Disease: Symptoms, Causes, Diagnosis, and Lifelong Treatment covers a copper disorder found during liver test work-ups.
Primary Biliary Cholangitis (PBC): Complete Guide to Symptoms, Causes, Diagnosis, and Treatment explains a bile duct disease that raises alkaline phosphatase.
Elastography: Types, Preparation, What to Expect and Liver Fibrosis Stages explains the painless stiffness test that stages liver scarring without a biopsy.
Bilirubin Test: Normal Levels, High Bilirubin Causes and Newborn Jaundice explains the blood test that measures bilirubin and what high levels mean.
Ceruloplasmin Test: Wilson Disease, Copper and What Results Mean explains the copper-carrying protein blood test used to check for Wilson disease.
References
Cleveland Clinic. Liver Function Tests: Types, Purpose & Results Interpretation. Cleveland Clinic. Last updated November 9, 2022. https://my.clevelandclinic.org/health/diagnostics/17662-liver-function-tests
Kwo PY, Cohen SM, Lim JK. ACG Clinical Guideline: Evaluation of Abnormal Liver Chemistries. Am J Gastroenterol. 2017;112(1):18-35. PMID 27995906. https://doi.org/10.1038/ajg.2016.517
Kim HC, Nam CM, Jee SH, et al. Normal serum aminotransferase concentration and risk of mortality from liver diseases: prospective cohort study. BMJ. 2004;328(7446):983. PMID 15028636. https://doi.org/10.1136/bmj.38050.593634.63
Medical disclaimer
This article is for general education only and does not replace advice from a qualified healthcare professional. Talk to your doctor about your own diagnosis and treatment, and seek emergency care right away for severe or sudden symptoms.
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