The liver is a large vital organ that performs many critical functions to maintain health and sustain life. It is located at the right upper portion of the abdomen just below the right side of the chest, extending into the middle portion of the abdomen. To understand what liver function tests are and why they are taken, it is first necessary to know more about liver function.
Important Functions of the Liver
The liver is a complex organ that:
- Manufactures proteins, including blood clotting factors and albumin
- Synthesizes, stores and metabolizes fats, fatty acids and cholesterol
- Metabolizes carbohydrates and stores them for energy
- Forms and secretes bile, which contains the bile acid necessary for absorption of fats and vitamins
- Metabolizes, secretes and eliminates harmful endproducts produced from normal body processes, including bilirubin and ammonia
- Metabolizes, secretes and detoxifies environmental toxins, drugs and alcohol taken into the body
The liver, therefore, aids in many bodily functions, such as digestion, excretion, supplying the body with energy, protecting the body from bleeding to death, and more. When one or more of these functions are disrupted by disease or injury, symptoms may not occur immediately because of the large liver reserve that protects and restores its function. It usually takes a significant amount of damage, which may occur over time, before symptoms arise.
Symptoms of Liver Disease
When liver function is affected by disease or injury, these symptoms may occur:
- Yellowing of the skin and white portion (sclerae) of the eyes – due to the liver’s inability to metabolize and secrete bilirubin, which has a yellow pigment
- Easy bruising or bleeding – due to the liver’s inability to produce enough blood clotting factors
- Edema, or swelling of legs – due to the liver’s inability to synthesize albumin
- Other symptoms like fatigue, loss of appetite, right-sided abdominal pain
These symptoms often manifest late into the disease process, usually when chronic or advanced liver disease has developed. Therefore, sometimes, in the presence of risk factors, doctors may request for a liver function test to be done to screen for certain conditions or to confirm a suspected disease before proper treatment is prescribed.
Liver Function Tests
A liver function test (LFT), also known as liver panel or liver enzyme test, is used to check the level of proteins and enzymes in the blood. It is done by taking a blood sample from a large vein (usually in the arm), which is then taken to the laboratory for evaluation. An increase or decrease in these levels may indicate the presence of a liver problem. LFTs may also be done to screen for hepatitis infection, to monitor the severity or progression of a liver disease, and to monitor for possible side effects of drugs. Certain risk factors such as obesity and chronic alcohol abuse may predispose patients to liver disease, so doctors may check for abnormal liver function as needed. Some of these tests are non-specific and additional blood tests may be required to make a more accurate diagnosis of certain liver diseases.
Common LFTs may include the following tests:
- Total protein and albumin. The liver synthesizes many proteins, including albumin, which the body needs to perform many functions, including fighting infections. Levels of albumin that are lower than normal may indicate liver disease but it may also be associated with other problems such as malnutrition.
- Bilirubin. This substance is produced normally from the breakdown of aging red blood cells. Bilirubin is metabolized by the liver before it is excreted in the stool. Elevated bilirubin levels may result in jaundice and usually indicates damage or liver disease. Other conditions associated with increase bilirubin include gallbladder disease and hemolytic anemia.
- Alanine transaminase or ALT. This liver enzyme helps the body to metabolize protein. ALT is almost exclusively found in the liver and is usually released into the blood in increased amounts with liver damage. It was formerly called SGPT (serum glutamic pyruvic transaminase).
- Aspartate transaminase or AST. This enzyme helps metabolize an amino acid called alanine. It is found in muscles and other tissues. Normally found in the blood at low levels, AST increases with certain disease, including liver disease. AST was formerly called serum glutamate-oxaloacetate transaminase (SGOT).
- Alkaline phosphatase or ALP. This enzyme is present in the bone, liver, and bile ducts, and elevated blood levels may indicate bone disease, liver disease ore bile duct disease.
- Gamma-glutamyltransferase or GGT. GGT is an enzyme present in the blood. Increased levels of GGT may indicate liver disease or damage of the bile duct.
- L-lactate dehydrogenase or LD. This is another enzyme found in many tissues including the liver. Although non-specific, increased LD levels may suggest liver damage.
- Prothrombin time or PT. This test checks the amount of time it takes the blood to form a clot. If higher than normal, it may indicate that there are low levels of blood clotting factors, which may be due to liver disease. PT may be done together with PTT (partial thromboplastin time) and INR (International normalized ratio), which are not strictly liver function tests, but are standard methods for laboratories to report PT.