Liver function tests, also referred to as a hepatic panel, are groups of blood test that measures the levels of several substances (enzyme and proteins) excreted by your liver. Abnormal levels can indicate liver problems, whether higher or lower levels.

Before we understanding liver function test. We must have to know what is liver and what functions of liver are. Here is short over review.

What is liver?

        Liver is the largest solid organ inside the human body. It’s located in the upper right abdomen, just below the diaphragm. Liver is the powerhouse organ that performs many essential functions to keep   your body healthy.

Here are some main functions of Liver:

• Filters blood: The liver acts as a filter for the blood coming from the digestive system. It removes toxins, such as alcohol, drugs, and waste products, from the bloodstream before they can circulate throughout the body.

• Produces bile: Bile is a fluid that helps break down fats in the small intestine so they can be absorbed into the body.

• Stores nutrients: The liver stores essential nutrients, such as vitamins A, D, E, K, and B12, as well as iron and copper.

• Regulates blood sugar: The liver helps to regulate blood sugar levels by storing glucose (sugar) as glycogen and releasing it back into the bloodstream when needed.

• Fights infection: The liver produces immune factors that help to fight infection.

• Excretory function: The liver helps eliminate waste products from the body through bile and urine.

• Synthesis of plasma proteins: The liver produces many important proteins found in blood plasma, including albumin, clotting factors, and carrier proteins that transport hormones, vitamins, and other substances throughout the body.

• Enzyme activation: The liver activates enzymes that are essential body functions, including digestion, metabolism, and detoxification.

• Metabolic function: The liver plays a critical role in metabolism, the process by which your body converts food into energy. It breaks down carbohydrates, proteins, and fats, and stores excess glucose as glycogen, which can be converted back to glucose for energy when needed.

• Circulatory function: The liver helps regulate blood volume and pressure. It also generates albumin, a protein that aids in maintaining the integrity of blood vessel walls by preventing fluid leakage.

• Hemoglobin function: The liver removes old red blood cells from circulation and breaks down hemoglobin, the protein in red blood cells that carries oxygen.

Here are several biochemical parameters of Liver Function test:

1. Bilirubin (Conjugated and Unconjugated).
2. Alanine Aminotransferase (ALT).
3. Aspartate Aminotransferase (AST).
4. Alkaline Phosphatase (ALP).
5. Gamma Glutamyl Transpeptidase (GGTP).

Here is detail information on each parameter or test of LFT:

Let’s now see each of them, one by one:

Bilirubin: Bilirubin is a breakdown product of hemoglobin. When RBC’s complete their life span, which is 120 days, they are destroyed in the body and hemoglobin is released. This hemoglobin further breaks down into heme and globin component. The heme component is converted into biliverdin which further converts into bilirubin. This bilirubin in unconjugated (also called indirect) form which is insoluble in water. So, it binds with albumin and the transported to liver. In the liver, Bilirubin is converted in conjugated form which is water soluble and can be easily excreted through urine or faeces. So, if there is increase in bilirubin level, it indicates that something in wrong in your liver. The main causes of bilirubin level in blood are:

• Hemolysis i.e. breakdown of RBCs.
• Failure of conjugating system in liver.
• Obstruction in the biliary system.

Aspartate Aminotransferase (AST): AST was previously called SGOT, serum Glutamate Oxalocetate Transminase.AST is an enzyme that helps metabolize amino acids. AST is high in Heart muscle, liver and Skeletal muscle, but low in Kidneys, Pancreas, RBCs. Damaged tissues release AST in blood. Therefore, AST level in blood is directly related to extent of cellular damage or injury. AST level in plasma is elevated hours after cellular injury, peak at 24 to 36 hours, and return to normal in 3 to 7 days. AST in blood is always high in patients with:

• Chronic Hepatocellular Disease.
• Acute Hepatitis.
• Acute Extra Hepatic Obstruction.
• Cirrhosis.

Factors which interfere with serum AST levels include:

• Pregnancy, in which there is decrease in AST level.
• Exercise, which increase levels of AST.
• Drugs, such as antihypertensives and oral contraceotives.

• Alanine Aminotransferase (ALT): ALT was previously called which stands for serum Glutamte Pyruvate Transaminase. ALT is an enzyme that found in liver, that helps convert proteins into energy for the liver cells, lesser quantities of ALT present in kidneys, Heart and Skeletal muscle. Liver injury triggers an elevation of ALT level in blood. ALT is more liver sensitive or specific indicator of liver disease, as compared to AST. Its level is directly related to extent of liver injury, and raised level of ALT can be seen in chronic alcoholism, hepatic cancer and chronic cirrhosis.

• Alanine Phosphatase (ALP): ALP is an enzyme found in liver, bones and placenta. This test low specificity for liver disorder because are other conditions that can also increase ALP levels. These are Cholestasis, in which there is obstruction of intra or extra-hepatic bile ducts. Pregnancy, bone disease specifically osteoblastic cancers and Paget’s disease. New bone growth can also cause elevation in ALP levels. So, because of these uncertainties another test is performed called GGT.

• Gamma Glutamyl Transpeptidase (GGTP): This test is highly accurate in indicting Cholestasis. It is the most sensitive liver enzyme for detecting Biliary Obstruction, Cholangitis or Cholecystitis. GGTP level is very high in liver, but low in Kidney, Heart, Intestine, Brain and Prostate gland. Elevation of GGTP parallels that of ALP in liver disease, but GGTP is not increased in bone disease. So, if ALP increased but GGTP levels are normal that indicates bone disease.

LFT’s PROFILE AND NORMAL VALUES.

                        LIVER FUNCTION TESTS (LFTs)