Introduction:
The liver tests are also called liver function tests (LFT). The liver function tests are done to check if a person has got an infection or to check the severity of the already prevailing liver disease. The LFT shows the levels of some proteins (like albumin and globulin), bilirubin (a substance produced by the liver during the breakdown of red blood cells), and enzymes (like AST- aspartate transaminase, LD - lactate dehydrogenase, GGT- gamma-glutamyltransferase and ALP - alkaline phosphatase) in the blood produced by the liver. When the values of these proteins or enzymes show levels beyond their normal range, liver disease is ruled out. Further treatment will be recommended by the doctor depending on the results and clinical symptoms.
Why Is the Liver Function Test Done?
When a person has symptoms like abdominal pain, jaundice (yellowish discoloration of the skin and eyes), fever, dark-colored urine, pale-colored stools, and swelling in the legs and ankles, LFTs are done to rule out any infection (viral or parasitic). The LFTs are also done to check the severity of the already prevailing liver diseases like cirrhosis (scarring of liver tissues), to check the clotting time, and to check the liver condition of a person who is under long-term medications like a pain killer.
LFTs also show the difference between acute (short-term) and chronic (long-term) liver disease. It also shows the difference between hepatitis (swelling or infection of the liver) and cholestasis (a problem with the bile flow). LFTs are also done to keep a check on the health status of the liver.
What Are the General Symptoms of Liver Diseases?
The general symptoms are as follows:
- Nausea or vomiting.
- Poor appetite.
- Yellowish discoloration of skin and eyes (jaundice).
- Fatigue and tiredness.
- Dark-colored urine or light-colored stools (less common).
- Abdominal swelling (less common).
When Is a Liver Function Test Suggested by a Physician?
Liver function tests are suggested if:
- One is a chronic alcoholic or has an alcohol use disorder.
- Family history of liver disease.
- Obese individuals.
- Those with high blood pressure and diabetes.
- Taking medications that can have an impact on the liver.
- Have anemia or gallbladder disease.
How Is the Liver Function Test Done?
The doctor or a lab technician will draw or extract 10 ml of blood with the help of a syringe from the vein in the arm. The blood will be drawn from the inner part of the elbow into a vial (a small tube for collecting blood samples). The area from where the blood is obtained will be cleaned before drawing the blood. Instructions, like not eating food or drinking fluids before 8 to 12 hours of the test, need to be followed.
Certain medications like Aspirin, Tylenol, Aleve, and Voltaren cause the increase of certain enzymes like aspartate transaminase (AST) and alkaline phosphatase (ALT). These medications need to be stopped the previous night before undergoing liver function tests. It is mandatory to discuss the list of drugs including over-the-counter medications and herbal supplements that one takes with the doctor to avoid getting abnormal results.
What Do Liver Function Tests Contain?
Various liver function tests are as follows:
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Serum Bilirubin Test: This is a diagnostic method to test for jaundice. Bilirubin is manufactured by the liver during the breakdown of red blood cells. The liver discards or removes the bilirubin from our body. If there is liver damage, the liver fails to eliminate the bilirubin from the body, due to which there is an abnormal collection of bilirubin in the blood. This results in jaundice, a condition that causes yellowish discoloration of the skin and eyes. High levels of bilirubin indicate liver disease. The normal level of bilirubin is 1.2 mg/dL and 1 mg/dL in young people under the age of 18.
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Serum Albumin Test: Albumin is a protein produced by the liver. Albumin maintains the flow of fluids in the blood within the blood vessel. It also helps the movement of enzymes, hormones, medications, and nutrients like vitamins throughout the whole body. If the levels of albumin are lower than the normal range, it indicates liver disease. The usual range of albumin in the blood is 3.4 mg/dL to 5.4 mg/dL.
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Estimation of the Levels of Serum Aminotransferases or Transaminases: Transaminases are enzymes that involve in a reaction that speeds up the conversion of alpha-amino acids (these help the body to break down food). When there is liver damage, the levels of aminotransferase are increased. The enzymes are released into the blood by the damaged liver cells. The normal level of serum aminotransferases ranges from 30 to 50 (IU/L).
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Alkaline Phosphatase Test (ALP): Alkaline phosphatase is an enzyme that helps in protein breakdown (a simpler form that the body can absorb). It is also present in bones, intestines, pancreas, and kidneys. When there is liver damage, the ALP leaks into the blood and there is a peak in the levels of ALP in the blood. High levels of ALP also indicate a bone problem. The normal ALP level ranges from 44 to 147 (IU/L). Some organizations report 30 to 120 (IU/L) as normal levels. Depending on the laboratory’s reference range, the normal values may vary.
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Alanine Transaminase Test (ALT): Alanine transaminase is an enzyme found in the liver, heart muscle, and kidneys but is mainly found in the liver. It helps the liver to break down protein and convert it into energy. If the liver gets damaged, the liver cells release ALT into the blood, causing elevated levels of ALT. The normal level of ALT is 7 to 56 (U/L). Some laboratories suggest 4 to 36 U/L. Normal ranges of ALT differ with different labs.
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Aspartate Transaminase Test (AST): Aspartate transaminase is an enzyme produced by the liver. It helps in the production of amino acids that help break down food. It is also present in the muscles of the heart, kidneys, and brain. When there is liver damage, AST is spilled into the blood, thus resulting in increased levels. The normal level of AST is 8 to 33 (U/L).
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Gamma-Glutamyl Transferase Test (GGT): GGT is produced in the liver. It helps in the chemical alteration of the medications so that the body can use and remove its wastes from the body. GGT is also found all over the body. High levels of GGT reveal liver disease or bile duct damage. The bile duct is a tube-like structure that carries bile from the liver to the gallbladder and small intestine. During liver damage, GGT is released into the blood, resulting in increased levels of GGT. The normal range of GGT is (5 to 40 U/L).
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Estimation of the Levels of Lactate Dehydrogenase (LD): Lactate dehydrogenase is a type of protein present in the liver and helps the body cells to change food into energy. When the liver is damaged, it releases LD into the blood. Increased levels of LD denote damage to the liver. The normal range of LD is 105 to 333 (IU/L).
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Prothrombin Time (PT): Prothrombin time is the time taken for the blood to clot (thickening of the blood). Blood clotting is carried out by vitamin K and a protein called fibrinogen. Fibrinogen is produced in the liver. Fibrinogen helps in blood clotting, wound healing, and the formation of new blood vessels. When there is liver disease or liver damage, the blood can take a longer time to clot. If the clotting time is within the normal limits, the liver is healthy. The normal range of prothrombin time is 11 to 12.5 seconds.
Additional Liver Tests:
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Alpha-Fetoprotein (AFP) Test: AFP proteins are produced from the liver cells that renew after damage. If the AFP results are elevated in the blood, liver cancer can be ruled out along with some imaging techniques like ultrasound or CT (computed tomography) scans. The elevated AFP levels are also used to find out other types of cancer like ovarian cancer, testicular cancer, and cancer of the lymphatic system (a system that fights germs attacking the body) called Hodgkin's lymphoma. AFP levels are also elevated in pregnant women, which is normal, as the liver of a developing baby inside a mother's womb also produces AFP. The normal range of AFP is 10 to 20 ng/mL.
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Mitochondrial Antibodies Test: Mitochondrial antibodies are present in the blood of patients with primary biliary cirrhosis (infection or swelling of the bile duct - a tube that connects the liver to the gallbladder and small intestine). These antibodies are formed against mitochondria (a substance that produces energy for the cells in the body) as an autoimmune response (when the body’s immune system attacks its own cells). These antibodies are also seen in increased levels in patients with autoimmune diseases and long-term liver infections or swelling (chronic hepatitis). The mitochondrial antibody test shows negative if the level is less than 0.1 units, borderline if it is between 0.1 - 0.3 units, weakly positive if it ranges between 0.4 - 0.9 units, and positive if the value is 1.0 units or more.
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Serum Alpha-1 Antitrypsin (AAT) Test: AAT is a protein produced by the liver for the protection of the lungs from disease or damage. If the levels of AAT in the blood are low, the risk of getting liver disease and chronic obstructive pulmonary disease (a long-term lung disease that causes blockage of airflow) is high before 45 years of age. The normal range of AAT ranges from 80 to 220 mg/dL.
How Long Will It Take for the Liver Function Results to Arrive?
The liver function test results may take a few hours or a day to be issued. From the results, low or elevated levels can be compared with normal values. Interpretation of the results requires expertise and hence a healthcare professional can aid in deciphering the results. If the results signify a problem with the functioning of the liver, the doctor will enquire about the previous medical and medication history to find out the cause.
Conclusion:
Liver function tests are done to eliminate any possible liver damage or liver disease. They are usually safe and involve minimal risks. One can experience a bruise or soreness at the site where the blood is drawn. If the results are normal, there is nothing to worry about. If the results are abnormal, the disease will be correlated with the symptoms, and treatment will be started. Early detection of the disease and performing regular liver function tests every year can prevent liver failure or damage.
