Short answer
Liver function tests, often called LFTs or a liver panel, are blood tests that measure several substances related to the liver. They can help show whether the liver may be inflamed, injured, affected by a medicine, having bile-duct problems, or not making or clearing certain substances normally. They usually cannot diagnose the exact cause by themselves.
What liver function tests commonly include
| Marker | What it is | How it is used |
|---|---|---|
| ALT | Alanine aminotransferase, an enzyme found mostly in the liver. | Often rises when liver cells are irritated or injured. |
| AST | Aspartate aminotransferase, an enzyme found in the liver and other tissues. | Interpreted with ALT and the rest of the panel, because AST is not liver-only. |
| ALP | Alkaline phosphatase, an enzyme found in the liver, bile ducts, bone, and other tissues. | Can point toward liver or bile-duct patterns, but high ALP can also come from bone and other causes. |
| GGT | Gamma-glutamyl transferase, an enzyme often used with other liver markers. | May help clarify whether an ALP pattern is liver-related. |
| Bilirubin | A waste product from the normal breakdown of old red blood cells. | The liver helps process and remove bilirubin; higher levels can relate to jaundice or bile-flow issues. |
| Albumin and total protein | Proteins made mainly by the liver. | Can reflect liver-making function, nutrition, inflammation, kidney loss, and other context. |
| PT/INR | A measure of how long blood takes to clot. | Because clotting proteins are made in the liver, this may be used in some liver evaluations. |
Why liver tests may be ordered
MedlinePlus says liver function tests may be used to check whether liver disease or damage could be causing symptoms, monitor known liver disease, see how treatment is working, or check side effects from medicines that can affect the liver. Some liver-related tests are also part of a routine comprehensive metabolic panel.
Symptoms and risk situations
A clinician may consider liver testing when symptoms such as fatigue, weakness, nausea, loss of appetite, jaundice, abdominal swelling or pain, ankle or leg swelling, dark urine, light-colored stool, or frequent itching raise concern. Testing may also be used when a person has higher liver-risk context, such as certain medicines, hepatitis exposure, diabetes, obesity, alcohol use disorder, or family history of liver disease.
Preparation
Follow the instructions from your clinician or lab. MedlinePlus notes that you will probably need to fast for 10 to 12 hours before some liver function testing, and that medicines can affect results. Do not stop prescribed medicines unless the ordering clinician tells you to. For general prep questions, see the fasting for blood tests guide.
What abnormal results can and cannot prove
Abnormal liver function tests do not always mean liver disease. Results are interpreted as a pattern, not as isolated numbers. For example, MedlinePlus notes that high ALP can be related to bone disease or liver disease, and that recent illness may cause temporary abnormalities. A clinician may compare ALT, AST, ALP, bilirubin, albumin, symptoms, medicines, medical history, and prior results before deciding whether to repeat testing or order additional tests.
Questions to ask
- Which markers were abnormal, and what pattern do they form together?
- Were ALT and AST elevated, or was ALP or bilirubin the main change?
- Could recent illness, alcohol, supplements, exercise, or medicines have affected the result?
- Should I repeat the panel, and if so, when?
- Do I need related testing, such as hepatitis B or hepatitis C testing, imaging, GGT, PT/INR, or a referral?