The liver is a body organ located in the right upper portion of the abdominal cavity, just beneath the rib cage. The liver performs a variety of functions that are vital to life. Some of the most important functions of the liver are:
- Detoxifying of blood
- Metabolizing nutrients and medications
- Producing important clotting factors, albumins, and other important proteins
- Processing of hemoglobin and other cells’ waste products
- Storing of fat, vitamins, bile, and cholesterol
- Producing glucose or glucose synthesis during starvation
Common Liver Blood Functions Tests
Liver blood tests are among the most commonly performed blood tests. The tests are used to assess liver functions or detect liver injury. A simple blood test that determines the level of some liver enzymes is the first step to detect liver damage. These enzymes usually reside within the liver cells in normal circumstances. But when there is a liver injury caused by any reason, the enzymes spilled into the bloodstream. Enzymes are a type of protein that can be found throughout the body, each one having its unique function. Enzymes catalyze routine and vital chemical reactions in the body.
Aminotransferases are among the most widely used and sensitive liver enzymes. They include aspartate aminotransferase - AST or SGOT - and alanine aminotransferase - ALT or SGPT, enzymes that are predominantly contained within the liver cells and to some extent in the muscle cells. When there is injury or damage, the liver cells spill the enzymes into the bloodstream, raising AST and ALT enzyme blood levels, which signal liver disease.
Other blood tests to check on the health of the liver are measurements of some other enzymes found in the liver. Other enzymes located in the liver include alkaline phosphatase, gamma-glutamyl transpeptidase or GGT.
Other names for various liver enzymes include:
- Aminotransferase is also known as transaminase
- Aspartate aminotransferase or AST is also known as serum glutamic oxaloacetic transaminase or SGOT
- Alanine aminotransferase or ALT is also known as serum glutamic pyruvic transaminase or SGPT
1. Aminotransferases Enzymes (ALT) test
These enzymes catalyze chemical reactions where an amino group from one amino acid is transferred from a donor molecule to a recipient molecule, which explains the names aminotransferases. ALT is used by the body to metabolize protein. When there is damage to the liver or when it does not function properly, ALT can be released into the blood.
An ALT test that shows higher than normal results can be a sign of liver damage.
The American College of Gastroenterology recommends that an ALT result that is higher than 15 IU/L in females and 33 IU/L in males would require further evaluation and testing.
2. Aspartate aminotransferase (AST) test
AST is an enzyme that can be found in many parts of the body, such as the liver, heart, and muscles. AST levels are not specific markers for liver damage as ALT. AST is usually measured together with ALT to check for problems in the liver.
When there is damage to the liver, AST can be released into the bloodstream. A high AST result could indicate a problem with the muscles or liver.
The normal range for AST is usually up to 40 IU/L in adults and higher in infants and young children.
3. Alkaline phosphatase (ALP) test
ALP is an enzyme found in the bile ducts, bones, and liver. An ALP test is usually ordered as one of several tests.
High ALP levels may indicate inflammation of the liver, a bone disease, or blockage of the bile ducts.
Children and adolescents could have elevated levels of ALP because of the growth of their bones. ALP levels can rise with pregnancy. The normal ALP range is up to 120 U/L in adults.
4. Albumin test
Albumin is the main protein produced in the liver. It has many important functions in the body, including:
- It stops fluid from leaking from the blood vessels
- It provides nourishment for the tissues
- It transports vitamins, hormones, and other substances throughout the body
An albumin test measures how well the liver makes this particular protein. A low result of the test indicates that the liver does not function properly.
The normal albumin range is from 3.5 - 5.0 grams per deciliter (g/dL). Low levels of albumin could also result from poor nutrition, infection, kidney disease, and inflammation.
5. Bilirubin test
The breakdown of red blood cells produces a waste product - bilirubin. It is ordinarily processed by the liver, passing through the liver before excreted through the stool.
When the liver is damaged, it cannot properly process bilirubin, which leads to an abnormally high level of bilirubin in the blood. A high level of bilirubin in the test may indicate that the liver does not properly function.
The normal bilirubin range is typically 0.1-1.2 mg per deciliter (mg/dL). Some inherited diseases raise the bilirubin levels even when the liver is normally functioning.
6. Platelet count
A test result showing low platelet count has many possible causes, including advanced liver disease. The normal platelet counts should be between 150,000 to 400,000 per (µL).
The body maintains the glucose level by a variety of mechanisms. The liver can release glucose in the blood to nourish the cells when they are starved due to insufficient oral glucose intake. The process, called gluconeogenesis, is one of the major functions of the liver. When liver diseases become advanced, this liver function can result in very low glucose levels because of poor oral intake. A large number of people with liver cirrhosis are glucose intolerant and develop diabetes.
8. Gamma-glutamyl transpeptidase (GGT)
This enzyme indicates possible liver damage. The higher is the abnormal level, there is more likelihood of liver damage. Normal levels of GGT are from 9 to 48 U/L.
9. Lactate dehydrogenase (LD or LDH)
This enzyme may become elevated in many types of diseases, such as liver disease. Normal levels of LD or LDH are from 122 to 222 U/L.
AST and ALT rest results and liver function
ALT and AST levels do not automatically reflect the function of the liver, although they are commonly referred to in the medical community as liver function tests. The liver may function properly even when AST and ALT results showed that they are elevated. When you have elevated liver enzymes or you get a high or abnormal liver test, you have to ask your doctor what all of those tests indicate.
What are liver functions tests used for?
Liver function tests are often used to:
- Diagnose liver disease, such as hepatitis
- Monitor the treatment of liver diseases. The tests will show how the treatment works
- Check the extent of the liver damage or the scarring by a disease, such as cirrhosis
- Monitor side effects of certain medicines
Why are liver function tests needed?
If you have symptoms of liver disease, you may need a liver function test. Various symptoms indicate there is a disorder in the liver. Some of those symptoms include:
- Fatigue or loss of energy
- Jaundice or yellow color of the skin and eyes
- Weight loss
- Ascites or fluid collection in the abdomen
- Discolored bodily discharge such as light stools or dark urine
- Abdominal pain
- Abdominal bleeding or bruising
Your doctor will usually order a liver function test when you experience symptoms of a liver disorder. The various liver function tests can monitor the progression or treatment of disease and test for side effects of some medications.
Your doctor may also order the different liver function tests if you have certain risk factors. You may be at higher risk of liver disease if you:
- Have a family history of liver disease
- Think you have been exposed to a hepatitis virus
- Have alcohol use disorder, a condition where it is difficult to control how much you drink
- Take medications that can cause liver damage
Getting a liver function test
Before you undergo a liver function test, your doctor will give you a list of instructions on how to prepare for the blood sample part of the test.
Some foods and medications can affect the levels of the enzymes and proteins in the blood that needs to be tested. Your doctor may ask you to stop taking or avoid some medications, or he may ask you to avoid eating anything for a certain period before the test. Continue drinking before the blood test.
Wear something comfortable such as a shirt with easily rolled-up sleeves. This will make the collection of blood samples easier.
The liver function test
Your blood will be drawn either in a hospital or at a specialized testing facility. To administer the test:
- The healthcare provider will clean the skin before the test to decrease the possibility that microorganisms on your skin could cause an infection.
- The healthcare provider will wrap an elastic strap on your arm to help the veins become more visible. A needle will be used to draw blood samples from your arm.
- After drawing the blood, the healthcare provider will put some gauze and a bandage over the puncture site. The blood sample will then be sent to a laboratory for testing.
Evaluation of a person’s liver blood values
Serial testing of AST, ALT, and other enzymes over time determines whether the levels are increasing, staying stable, or decreasing. When an individual is treated for chronic hepatitis C, he is typically monitored using serial liver enzyme tests. The individuals who respond to treatment will experience lowering of liver enzyme levels to normal or almost-normal levels. Individuals whose hepatitis C relapsed after treatment typically develop elevated abnormal enzymes again.