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Decoding the basic liver function tests

Decoding the basic liver function tests

A timely update on liver health is vital, especially for people above 30

Liver function tests are a group of blood tests used to help diagnose and monitor liver disease or damage

The liver is involved in multiple metabolic, gastric, filtration and hormonal functions. It is also the largest organ in our body and also weighs over one kilogram.

Apart from producing cholesterol for strengthening our cellular structure, the liver also maintains the chemical balance in our blood, secretes bile juice which helps to filter out metabolic waste, aids in fat digestion and stores glucose in the form of glycogen. The liver could also be considered a gland because of the secretion of bile juice and its hormonal functions, especially in the chemical conversion of thyroid hormone.

The liver proteins and enzymes

Multiple enzymes and proteins are synthesised in the liver. This is in addition to its role in secreting albumin, another protein that regulates blood volume.

The proteins produced in the liver are involved in cellular activities including digestion and the transportation of cholesterol in the blood across the body.

The liver also produces enzymes that speed up the chemical and molecular functions within our body including amino acid (protein) metabolism. The main enzymes made in the liver cells and bile ducts include alkaline phosphatase (ALP), alanine transaminase (ALT), aspartate transaminase (AST) and gamma-glutamyl transferase (GGT). However, these enzymes should not be found in the blood if the liver is healthy. They leak into the bloodstream only if there is a major liver infection or inflammation.

What are the liver functions tests?

“Liver function tests are a group of blood tests used to help diagnose and monitor liver disease or damage. These tests measure the levels of certain enzymes and proteins in the blood,” explains Dr Ravindra Nidoni, consultant, liver transplant surgery, Fortis Hospital, Bannerghatta Road, Bengaluru. High enzyme levels detected indicate hepatocyte (liver cell) damage.

According to Dr Prasanna Bhat KS, consultant, hepatology and transplant physician, Manipal Hospitals, Bengaluru, the liver function test does not require any preparation or fasting.

“It is advisable for those above the age of 30 to get a liver function test during their regular health check-up,” he adds.

These tests could keep our liver safe:

Albumin and total protein test

This test measures the total amount of protein in the blood.

Albumin maintains the osmotic pressure of the circulating blood and prevents it from leaking out of the blood vessels into the tissues. Albumin level indicates the liver’s protein synthesis function. “Within a month or so of liver damage, the albumin level starts going down,” explains Dr Bhat.

Dr Nidoni adds that low albumin and total protein value means the liver is not able to produce proteins crucial for cellular functions and vital functions like transporting essential molecules like lipids through the bloodstream.

Dr Bhat also adds that globulin levels are also checked during the liver function test. Globulin is a group of proteins found in the blood which help fight infections and also aid in blood clotting. The total albumin and globulin readings are used to calculate the albumin/globulin (A/G) ratio. If this ratio is above the permissible limit, then there could be a high chance of liver or kidney infection.

The alkaline phosphatase (ALP) test

This test measures the amount of ALP in the blood. The enzyme ALP is found throughout the body but mostly in the liver, bone, kidney and even digestive tract. “It is an important enzyme for breaking down proteins. But if the amount of ALP is higher than normal it could indicate liver cancer, cirrhosis, hepatitis or even a blockage in the bile ducts,” explains Dr Nidoni.

Alanine transaminase or (ALT) test

ALT is another enzyme found in the liver that helps convert proteins into energy for the functioning of the liver cells.

“If there is liver cell damage, ALT enzymes are released into the blood,” explains Dr Bhat. Dr Nidoni reiterated that high ALT values indicate either liver infections or obstructed blood flow to the liver. It could also indicate liver cancer and cirrhosis.

Aspartate transaminase (AST)

AST is another liver enzyme for amino acid metabolism. If AST is found in the blood it could indicate liver complications or muscle damage, says Dr Nidoni. Elevated AST could mean hepatitis, cirrhosis, mononucleosis (a viral infection) or other liver diseases. It could also indicate cardiac complications or pancreatitis.

Bilirubin test

Bilirubin is a pigment formed in the bile duct by the breakdown of haemoglobin. It is usually excreted out in the stool. “High levels of bilirubin in your blood is a warning sign that your liver is unable to clear bilirubin adequately,” says Dr Bhat. That’s why when people have jaundice, the bilirubin is high and indicates liver damage. High bilirubin levels could also be a result of some other liver conditions including cancer or pancreatitis. There are two types of bilirubin – the indirect type which circulates in the blood towards the liver and the direct type which undergoes changes in the liver and gets expelled through stool.

Gamma-glutamyl transferase (GGT) test

The GGT is an enzyme found in the liver, kidney and pancreas. “High GGT in the blood is due to alcohol abuse and indicates bile duct damage and fatty liver as well,” explains Dr Bhat.

Prothrombin time (PT) test

A prothrombin time test is a blood test that measures how long it takes for the blood to clot. An increased PT may indicate liver damage, but it can also be elevated if you’re on blood-thinning medication.

 “Abnormal PT value is a foremost sign of acute liver damage,” explains Dr Bhat.

The results are expressed as an international normalised ratio (INR) and the normal range for this is between 0.9 and 1.1.

Other liver health tests

Dr Bhat says that there are other liver tests prescribed for specific conditions. Some of them are:

  • For auto-immune hepatitis, multiple blood antibody tests would be required to distinguish autoimmune hepatitis from viral hepatitis.
  • Alpha-fetoprotein (AFP) test is done to predict hepatocellular carcinoma (a cancer that starts in the liver) risk for pregnant women. AFP is a plasma protein that the yolk sac and the foetal liver make during foetal development. It also helps to monitor treatment efficacy for hepatoma (liver cancer variant).
  • Mitochondrial antibodies test identifies primary biliary cirrhosis (a chronic disease in which the bile ducts in the liver gradually get damaged), chronic active hepatitis (when liver inflammation continues for at least six months) and autoimmune disorders.


A liver function test involves a simple blood test but can check the levels of enzymes and proteins which are great markers of liver health. Those above 30 years need to get a timely update on their liver status. These tests could also often reveal other underlying renal and gastric issues.

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