A liver function test (LFT) is a blood test that measures the levels of certain proteins and enzymes in your blood. These proteins and enzymes are produced by the liver, and they can be a good indicator of how well your liver is functioning.
Liver function tests are often ordered when someone has symptoms that might be related to a liver problem, such as fatigue, yellowing of the skin or eyes (jaundice), dark urine, or upper abdominal pain. They can also be ordered if you have a history of liver disease or if you’re taking medications that can affect the liver.
What the Test Measures
Many different proteins and enzymes can be measured in a liver function test, but the most common ones are:
- Albumin: This is a protein that is produced by the liver. Low levels of albumin can be a sign of liver damage.
- Alkaline phosphatase (ALP): This enzyme is found in high levels in the bile ducts. If there is blockage of the bile ducts, ALP levels will be high. ALP levels can also be high in certain bone diseases.
- Alanine transaminase (ALT): This enzyme is found in high levels in the liver cells. ALT levels will be high if there is damage to the liver cells.
- Aspartate transaminase (AST): This enzyme is found in high levels in the liver cells. AST levels will be high if there is damage to the liver cells.
- Bilirubin: Bilirubin is produced when red blood cells are broken down. Elevated bilirubin levels in the blood can indicate damage to the liver
- Gamma-glutamyltransferase (GGT): This is an enzyme that is present in the blood. Elevated levels of GGT can indicate damage to the liver. L-lactate dehydrogenase (LD): Although elevation in the enzyme lactate dehydrogenase can be present in other conditions, it can be elevated in liver disease as well.
- Prothrombin time (PT): PT time is measured as the time it takes your blood to clot. Elevated PT time can indicate damage to the liver.
Liver function tests are important tools that can help your doctor evaluate your liver health. If you have symptoms that might be related to a liver problem, or if you have a history of liver disease, your doctor may order a liver function test for you.
Your doctor may also choose to order a liver function test to monitor your liver while you are taking certain medications (like antifungals such as Terbinafine).
You should fast (nothing to eat or drink) for 8-12 hours before a liver function test. Certain medications like Coumadin can affect your results. Make sure to notify your doctor about this.
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