Lab test5 min read
Liver function tests
LFT
A group of blood tests that measure substances made by or affected by the liver, such as enzymes, albumin and bilirubin. They help doctors screen for and monitor liver problems.
According to MedlinePlus, this panel measures several substances made by the liver in a blood sample to assess its health and function. It includes proteins (albumin and total protein), enzymes (ALP, ALT, AST, GGT and LDH), bilirubin, a substance produced by the breakdown of old red blood cells, and prothrombin time (PT), which measures how long blood takes to clot. It is requested to screen for liver disease or damage, estimate its severity, monitor its progress and response to treatment, and find out the effects of drugs on the liver.
It is done on a venous blood sample, and fasting for 10 to 12 hours may be requested (MedlinePlus). MedlinePlus notes that abnormal results may indicate inflammation, hepatitis, impaired liver function, a problem in the bile ducts or drug-induced damage. The source page does not give reference ranges, so no numbers are given here. This page also does not cover the details of interpreting patterns of liver test results.
What is it?
According to MedlinePlus, liver function tests (the liver panel) measure several substances made by the liver in a blood sample to assess liver health and function.
The substances it includes according to MedlinePlus: albumin (a protein made by the liver), total protein, the enzymes ALP, ALT, AST, GGT and LDH, bilirubin (a product of the breakdown of old red blood cells), and prothrombin time (PT) (the time blood takes to clot).
Why is it done?
According to MedlinePlus, it is requested to check for liver disease or damage, estimate the severity of the disease once diagnosed, monitor its progress and the effectiveness of treatment, and find out the side effects of drugs on the liver.
Symptoms that prompt it, according to MedlinePlus: nausea, vomiting, loss of appetite, tiredness, weakness, yellowing of the skin and eyes, abdominal pain or swelling, swollen ankles or legs, dark urine, pale stools, itching.
Preparation
According to MedlinePlus: you will often need to fast for 10 to 12 hours before the test. Tell the provider about all the medicines you take.
How is it done?
A provider takes a blood sample from a vein in the arm with a small needle, and the process usually takes under five minutes (MedlinePlus).
Understanding the result
According to MedlinePlus, abnormal results may indicate inflammation, hepatitis, impaired liver function, a problem in the bile ducts, or drug-induced damage.
The source page did not give reference ranges, so no numbers are given here. Laboratories and guidelines differ, so what counts is your laboratory's report and your doctor's interpretation.
Risks and side effects
According to MedlinePlus: slight pain or a bruise may occur at the needle site, and most symptoms go away quickly.
Limits of the test
Interpreting the result depends on which substances have changed and on the symptoms and medicines, and the doctor decides it. This page does not cover the patterns of liver test results and their limits in detail.
When do you need urgent help?
See your doctor within days
- Yellowing of the skin or eyes, dark urine, pale stools, itching, swelling of the abdomen or legs, or persistent tiredness and nausea: these are symptoms MedlinePlus lists as reasons for requesting liver tests; see your doctor to have them assessed. This page does not specify the level of urgency.1
Educational content only — no diagnosis, and no substitute for a clinician.
Common questions
Do I need to fast?
According to MedlinePlus you often need to fast for 10 to 12 hours, so check with the laboratory.1
Does an abnormal result mean liver disease?
According to MedlinePlus, it may indicate inflammation, hepatitis, impaired function, a problem in the bile ducts or the effect of a drug; the doctor interprets it together with the clinical picture.1
Which substances are measured?
Albumin, total protein, the enzymes ALP, ALT, AST, GGT and LDH, bilirubin and PT.1
Questions for your doctor
- Which components of the liver panel have changed and what does that mean in my case?
- Might my medicines or supplements affect the liver or the result?
- Do I need to repeat the test or have imaging or other tests?
- When should I repeat the test?
References
- 1MedlinePlus / NLM. Liver Function Tests. medlineplus.gov/lab-tests/liver-function-tests/Health agencies & guidelines · Accessed 2026-10-07
- 2MedlinePlus. Liver function tests (encyclopedia). medlineplus.gov/ency/article/003436.htmHealth agencies & guidelines · Accessed 2026-10-07
Review status: Edited content · Last updated:
Change log
- — Page created.
Educational content only — no diagnosis, and no substitute for a clinician.