Overview of LFT
What is LFT?
Why is LFT done?
The Liver Function Test is performed:
As a part of a routine health checkup
To diagnose any suspected liver disease like viral hepatitis, alcoholic hepatitis, autoimmune hepatitis or to measure the extent of cirrhosis (scarring of the liver)
To monitor an existing liver disease and to evaluate the efficacy of the treatment being given for the same
To monitor the liver function in case you are taking some medicines, that are known to have a harmful effect on the liver
What does LFT Measure?
LFT measures the level of liver enzymes, proteins, and bilirubin in the blood.
The liver is a wedge-shaped organ located in the right upper part of the abdomen. The liver helps in the synthesis of certain proteins, produces bile (an alkaline compound which helps in the breakdown of fat), process the bilirubin (a yellowish substance produced from the breakdown of hemoglobin) and helps in removing ammonia and other toxins (harmful substances) from the body. It plays an important role in the metabolism of fats, protein, and carbohydrates. It stores glycogen, vitamins, and minerals as well as helps in the metabolism (breakdown) of certain drugs.
Many diseases affect the health of the liver like hepatitis A, hepatitis B, hepatitis C, alcoholic hepatitis, autoimmune hepatitis, cirrhosis, non-alcoholic fatty liver disease (NAFLD), bile duct obstruction, liver or bile duct cancer and many others. Liver function can also be affected by various risk factors like alcohol abuse, certain drugs, sedentary lifestyle, and obesity. Regular monitoring of liver function is essential for early detection of any liver abnormality.
LFT is a group of tests that measure the levels of Aspartate Aminotransferase (AST), Alanine Aminotransferase (ALT), Alkaline Phosphatase (ALP), Total protein, Bilirubin and Gamma Glutamyltransferase (GGT) in blood. Each component has its own significance and helps to understand a particular aspect of the liver function.
Alanine Aminotransferase (ALT)
Alanine Aminotransferase (ALT) is an enzyme and this test measures the level of this enzyme in the blood. ALT is also known as serum glutamic-pyruvic transaminase (SGPT) and is mainly found in the liver, but also in smaller amounts in the kidneys, heart, pancreas and muscles. This enzyme is released into the bloodstream in case of liver disease or damage leading to increased ALT blood levels, a specific indicator of liver injury. However, this test cannot determine the extent or severity of the liver damage.
Aspartate Aminotransferase (AST)
This test measures the level of the enzyme AST in your blood. It is also known as serum glutamic-oxaloacetic transaminase (SGOT). AST is found in the liver and is released in the blood in large amounts in case of any liver injury. AST levels are usually measured along with ALT as AST is not specific for liver (also found in the heart, skeletal muscle and other organs). Your doctor may also recommend an ALT/AST ratio to help in the diagnosis.
Alkaline phosphatase (ALP)
This test measures the blood levels of the enzyme ALP which is found in the liver (one of the main source), bile ducts, bones, intestine, pancreas and kidney. ALP helps to break down proteins in the body. Diseases that mainly harm or damage the cells of the liver and bile duct, leading to overproduction and release of this enzyme into the bloodstream. This causes increased blood ALP levels.
Total Serum Protein
This test measures the total amount of protein in the blood, which includes two major types of proteins: albumin and globulin. The test report mentions separate results for total protein, albumin, globulin and albumin/globulin ratio (A/G ratio).
The level of proteins in the blood indicates the biosynthetic capacity of the liver. Hepatocytes (liver cells) are unable to synthesize this protein in certain liver diseases leading to a fall in protein levels in the blood.
Albumin is synthesized only in the liver. It helps to transports minerals, enzymes, hormones, bilirubin and some medicines throughout your body. It prevents the fluid from leaking out of your blood vessels into the tissues.
Globulin is synthesized in the liver and by the cells of the immune system. It plays a key role in fighting infections and transports many enzymes, hormones, minerals and some medicines in the body.
This test measures the amount of bilirubin in the blood. Bilirubin is a waste product formed by the breakdown of red blood cells and is processed by the liver.
Bilirubin blood test report includes separate values for direct (conjugated) bilirubin, indirect (unconjugated) bilirubin, and total bilirubin.
When heme is released from the hemoglobin, it is converted to bilirubin. This is called unconjugated (indirect) bilirubin which is carried to the liver by some proteins.
In the liver, bilirubin gets attached (conjugated) to modified sugars (glucuronic acid) and form conjugated (direct) bilirubin.
Both these forms can be measured or estimated by laboratory tests, and a total bilirubin result (includes both direct and indirect bilirubin) is also measured.
A damaged liver can’t properly process bilirubin, leading to abnormally high levels of bilirubin in the blood. Increased unconjugated bilirubin in the blood results due to its overproduction or improper uptake by the liver. Increased conjugated bilirubin results can be seen in diseases that reduce the rate of secretion of conjugated bilirubin into the bile or the flow of bile into the intestine resulting in a backward flow of conjugated bilirubin into the blood.
This test measures the level of the enzyme GGT in your blood which is present in large amounts in the liver. It is a transport molecule and it helps the liver to metabolize many drugs and toxins. GGT is a very sensitive test for detecting any liver disease especially due to alcohol abuse and is also one of the first enzymes to rise in patients with bile duct obstruction like tumor or stones.
Preparation for LFT
- Do not eat or drink anything other than water for 8-12 hours before the test.
Sample Type for LFT
Interpreting LFT results
Alanine Aminotransferase (ALT)
The normal ALT levels range from 0-35 U/L.
Lower ALT levels indicate a healthy liver, however, lower levels can also be seen in patients with malnutrition.
A mild to moderate increase in ALT levels is seen in patients with the alcoholic liver disease, cirrhosis, chronic liver disease, bile duct obstruction, liver trauma or any physical injury, or patients taking certain medicines that are harmful to the liver.
A high increase in ALT levels is seen in patients with acute hepatitis like viral hepatitis (Hepatitis A, Hepatitis B, Hepatitis C) or in patients who have taken very high doses of some medicines like paracetamol.
Aspartate Aminotransferase (AST)
The normal AST test results range from 0-35 U/L.
Lower levels of AST in blood are considered normal, although very low levels are seen in cases of alcoholic liver disease and malnutrition.
High levels of AST is seen in patients with alcoholic liver disease (AST often increases much more than ALT), cirrhosis, chronic liver disease, bile duct obstruction, liver trauma, non-alcoholic fatty liver disease (NAFLD), viral hepatitis (Hepatitis A, Hepatitis B, Hepatitis C) and in patients taking medicines that are harmful to the liver or taking very high doses of some medicines like paracetamol. High levels of AST are also seen in patients with heart attack and muscle injury (however, ALT levels are normal in these patients). High level of AST with normal levels of ALT indicates that source of AST is not liver.
Alkaline phosphatase (ALP)
The normal level of ALP in blood is 13-100 μ/L
High levels of ALP are seen in patients with bile duct obstruction, hepatitis, cirrhosis, and in liver cancer.
High levels of ALP are also seen in growing children and pregnant women and are considered normal.
Low levels of ALP are seen in patients with malnutrition and certain genetic disorders. ALP levels also decrease temporarily after heart surgery and blood transfusion.
Total Serum Protein
The normal level of Total protein in blood is 5.5-8.0 g/dL.
Albumin & Globulin
The normal level of Albumin is 3.5-5.5 g/dL, approximately 50-60% and that of Globulin is 2.0-3.5 g/dL, approximately 40-50%. a normal A/G ratio of slightly over 1.
Albumin: Low levels indicate that you may be suffering from a disorder where the protein isn't synthesized, digested or absorbed properly. Lower levels are seen in patients with a chronic liver disease such as cirrhosis, inflammatory liver diseases like hepatitis, and in hepatocellular necrosis. Higher levels are seen in liver infections like Hepatitis A, Hepatitis B and Hepatitis C. High levels may also be seen if you are having a protein rich diet or if you are dehydrated.
Globulin: Low levels are seen in patients with malnutrition. High levels are seen in chronic active hepatitis and alcoholic hepatitis. It is also increased in acute infection, chronic inflammatory diseases.
A/G Ratio: Low A/G ratio is indicative of overproduction of globulin and reduced production of albumin, which occurs with liver cirrhosis. High A/G ratio often suggests the decreased production of globulins and is seen in some genetic diseases or leukemia.
The normal level of Total Bilirubin in blood is 0.3-1.0mg/dL.
The normal level of conjugated bilirubin (direct) 0.1-0.3mg/dL.
The normal level of unconjugated bilirubin (indirect) is 0.2-0.7mg/dL.
The lower levels are usually not a concern.
Unconjugated Bilirubin: Higher levels of unconjugated bilirubin are seen in patients with jaundice, acute hepatocellular damage, cirrhosis, viral hepatitis, alcoholic liver disease, bile duct obstruction, liver failure and in conditions involving an unusual amount of RBC destruction (hemolysis). Increased levels are also commonly seen in newborns, typically 1 to 3 days old. If the bilirubin levels do not return to normal and are increasing rapidly, this may indicate neonatal jaundice.
Higher unconjugated bilirubin levels compared to conjugated bilirubin is suggestive of transfusion reactions and cirrhosis.
Conjugated bilirubin: Higher levels of conjugated bilirubin are seen in patients with hepatitis, gallstones or inflammation of the bile duct (duct that carries bile from liver to the gut).
The normal level of GGT in blood is 9-48 U/L.
High levels of GGT are seen in patients with obstructive liver disease, acute and chronic viral hepatitis, cirrhosis, fatty liver disease, cholestasis, alcoholic liver disease, liver tumors and in case the patient is taking medicines like phenobarbitone, phenytoin, paracetamol and antidepressants. The low levels of GGT in the blood indicate the absence of liver disease and confirm no alcohol consumption.
There are other conditions as well in which high GGT levels are seen as heart failure, pancreatitis or diabetes. GGT levels are measured along with ALP. If both the enzymes are elevated, it indicates a liver disease. If GGT is normal and ALP is elevated, it indicates an underlying bone disease.
Note: Your doctor will interpret your results depending upon your gender, age, medications/treatment or diet you are taking.
Answers to Patient Concerns & Frequently Asked Questions (FAQs) about LFT
Frequently Asked Questions about Liver Function Test
Tests Included in Liver Function Test(11 tests)
- Aspartate Aminotransferase
- Gamma Glutamyl Transferase
- Alkaline Phosphatase
- Protein Total, Serum(includes 4 tests)
Albumin/Globulin Ratio, Serum
- Alanine Transaminase