Liver Function Test (LFT)

What is LFT?

Liver function test (LFT) includes a group of blood tests commonly performed to evaluate the function of the liver. This test measures the level of enzymes and proteins produced by the liver including bilirubin, albumin, lactate dehydrogenase etc. It is advised in case of symptoms suggestive of liver problems such as dark urine, diarrhea, light stool and jaundice.

LFT helps in the diagnosis of liver related conditions including liver cirrhosis, hepatitis and liver damage. It is also advised to patients undergoing treatment for liver disorders.

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.

 

Bilirubin

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.

 

Gamma-glutamyltransferase (GGT)

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.