LIVER FUNCTION TESTS (LFT)

Overview

Liver function tests are blood tests used to help find the cause of your symptoms and monitor liver disease or damage. The tests measure the levels of certain enzymes and proteins in your blood. Some of these tests assess how well the liver is performing its regular functions of producing protein and clearing bilirubin, a blood waste product. Other liver function tests measure enzymes that liver cells release in response to damage or disease.

Irregular liver function test results don't always mean liver disease. A member of your health care team will typically explain your results and what they mean.

Why It's Done

Liver function tests can be used to:

• Screen for liver infections, such as hepatitis.
• Monitor a disease, such as viral or alcoholic hepatitis, and determine how well a treatment is working.
• Look for signs of serious disease, particularly scarring of the liver, called cirrhosis.
• Monitor possible side effects of medicines.

Liver function tests check the levels of certain enzymes and proteins in your blood. Levels that are higher or lower than usual can mean liver problems. The pattern and degree of elevation of these tests, along with the overall clinical picture, can provide hints to the underlying cause of these problems.

Common Liver Function Tests

• Alanine transaminase (ALT): ALT is an enzyme found in the liver that helps convert proteins into energy for liver cells. Elevated levels of ALT may indicate liver damage. This test is sometimes referred to as SGPT.
• Aspartate transaminase (AST): AST helps the body break down amino acids. Higher levels may indicate liver damage, liver disease, or muscle damage. This test is sometimes referred to as SGOT.
• Alkaline phosphatase (ALP): ALP is found in the liver and bones. Elevated levels may indicate liver damage, a blocked bile duct, or certain bone diseases.
• Albumin and total protein: Albumin is a protein made in the liver. Low levels may indicate liver damage or disease, though they may also occur in kidney-related conditions.
• Bilirubin: A substance produced during the breakdown of red blood cells. Higher levels of bilirubin may indicate liver damage or disease, or conditions such as a blocked bile duct or certain types of anemia.
• Gamma-glutamyltransferase (GGT): GGT is an enzyme in the blood. Elevated levels may indicate liver or bile duct damage, although this test can also be elevated in conditions other than liver disease.
• L-lactate dehydrogenase (LD): LD is an enzyme found in the liver. Higher levels may indicate liver damage, though other conditions can also cause elevated LD levels.
• Prothrombin time (PT): PT is the time it takes for your blood to clot. Increased PT may indicate liver damage or may be caused by taking blood-thinning medications, such as warfarin.

Risks

The blood sample for liver function tests is usually taken from a vein in your arm. The main risk associated with blood tests is soreness or bruising at the site of the blood draw. Most people don’t experience serious reactions to having blood drawn.

How You Prepare

Certain foods and medicines can affect the results of your liver function tests. Your doctor may ask you to avoid eating food and taking some medicines before your blood is drawn.

What to Expect

During the Test

A blood sample for liver function tests is usually drawn through a small needle inserted into a vein in the bend of your arm. The needle is attached to a small tube to collect your blood. You may feel a quick pain as the needle is inserted, and experience some short-term soreness after it is removed.

After the Test

Your blood sample will be sent to a laboratory for analysis. If the lab is on-site, you may receive your results within hours. If your sample is sent to an off-site lab, results may take several days.

Results

Standard range results can vary slightly between laboratories, and they might differ based on factors like age, sex, and preexisting health conditions. Your healthcare team will use your results to help diagnose your condition or decide on any treatments you may need.

If you already have liver disease, liver function tests can help monitor disease progression and determine how well your treatment is working. Additional tests, such as blood tests or imaging, may be used to assist in diagnosis.