What is a liver function test?
A liver function test is a blood test in which the blood is examined in a laboratory to check for liver damage and the overall health of the liver. The levels of certain substances in the blood can help show if the liver is working properly.
What does the liver do?
The liver’s functions include:
- Filtering blood from the digestive tract
- Storing energy
- Processing waste products
- Removing poisons
- Producing proteins that help blood clot
- Producing glucose (blood sugar)
- Aiding in digestion
What do liver function tests check?
A liver function test checks the enzyme and protein levels in the blood. Enzymes found in the liver and other parts of the body include alanine transaminase (ALT), aspartate transaminase (AST), alkaline phosphatase (ALP), and gamma-glutamyl transpeptidase (GGT). High levels of these enzymes could mean damage to the liver or bile duct.
The liver also produces proteins, including albumin, globulin, and prothrombin. Low levels of these proteins could be a sign of liver damage. A prothrombin time test shows how long it takes for blood to clot.
A liver function test also measures platelet counts and glucose levels. (Platelets help the blood to clot in order to stop bleeding.)
The liver function test also measures bilirubin levels. Bilirubin is a fluid created from the breaking down of red blood cells. If the liver is damaged, bilirubin can leak out of the liver. This can cause the disease jaundice, in which the skin or eyes turn yellow. High bilirubin levels can also make urine darker in color.
What should I do to prepare for a liver function test?
Your healthcare provider may ask you not to eat, drink, or take certain medications in order to avoid affecting the test results.
Results and Follow-Up
What are normal laboratory ranges for liver function tests?
The laboratory that completes your test may use normal ranges that differ slightly. Check with your healthcare provider for the details.
What can cause abnormal results in a liver function test?
Several conditions can cause abnormal results in a liver function test, including:
- Diabetes mellitus
- Hepatitis B
- Hepatitis C
- Side effects of medications
- Acute hepatitis A
- Celiac disease (an autoimmune disease in which the person must avoid foods that contain gluten)
- Liver cancer
- Other illnesses and conditions
Talk with your doctor if you have any questions about your liver function test results.
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