Liver Function Tests Overview

The liver's ability to convert glucose into glycogen, a storage form of glucose.

The breakdown of glycogen back into glucose, releasing it into the bloodstream.

The process of creating glucose from non-carbohydrate sources, like amino acids or glycerol.

Liver synthesizes most of the coagulation factors, which are proteins involved in blood clotting.

The liver produces primary bile acids, essential for fat digestion and absorption.

The liver removes cholesterol from the bloodstream and eliminates it through the bile.

The liver metabolizes and inactivates steroid hormones, preventing them from circulating in excess.

The liver metabolizes and detoxifies drugs by breaking them down into inactive forms.

Liver function tests (LFTs) are a group of blood tests that assess the health of the liver. They can be used to detect and monitor liver disease, evaluate its severity, predict the outcome, monitor therapy, and assess prognosis.

Mild elevation in LFTs can be nonspecific and may normalize upon repeat testing. Further evaluation is typically required in context of the patient's clinical presentation.

Liver function tests (LFTs) are useful for screening liver dysfunction and recognizing patterns of abnormalities that can suggest the type of liver disorder. They can also assess the severity of the disease, follow the cause of liver disease, and monitor the response to treatment.

Liver function tests (LFTs) have limitations. They lack sensitivity meaning that normal results do not exclude serious liver disease. They are not specific for liver dysfunction, and may not lead to a specific diagnosis. Most importantly, a normal result in abnormal function test may not be reliable.

Bilirubin, a breakdown product of heme, is cleared from the blood by the liver (2-14 µmole/L). Elevated total bilirubin can be caused by several drugs, including anabolic steroids, antibiotics, antimalarials, ascorbic acid, diabinese, codeine, diuretics, epinephrine, oral contraceptives, and vitamin A.

Direct bilirubin is elevated in bile duct obstruction. Common causes include gallstones or cancer (0-4 µmole/L).

Alanine transaminase (ALT) is an enzyme necessary for energy production. It is present in various tissues, including the liver (hepatocytes), heart, and skeletal muscles. ALT rises dramatically in acute liver damage, such as viral hepatitis or paracetamol overdose (5-40 IU/L).

Liver function tests (LFTs) are broadly categorized into three groups: synthetic function (albumin, PT), hepatocyte injury (AST, ALT), and cholestasis (bilirubin, ALP, GGT). Of these, PT, albumin, and bilirubin are commonly used as prognostic factors in liver disease assessment.

Gamma-glutamyl transferase (GGT) is an enzyme found in the liver and other tissues. Elevated levels of GGT can indicate liver damage, especially when caused by alcohol consumption or certain medications.

Lactate dehydrogenase (LDH) is an enzyme found in many body tissues, including the liver. High LDH levels can indicate liver damage, but it's not specific to the liver.

Prothrombin time (PT) is a test that measures how long it takes for blood to clot. It's used to assess liver function because the liver produces most of the clotting factors needed for blood coagulation.

Ammonia is a waste product of protein breakdown. The liver normally converts ammonia into urea for excretion. Elevated ammonia levels can indicate severe liver disease.

Albumin is a protein synthesized by the liver. Decreased albumin levels are commonly seen in chronic liver diseases like cirrhosis.

An enzyme involved in the breakdown of proteins and the release of amino acids. It is elevated in conditions involving liver damage, but also in other tissues like muscles.

This enzyme plays a crucial role in carbohydrate metabolism. It's primarily found in the liver. Elevated levels may suggest liver damage, especially when combined with AST.

A group of enzymes responsible for transferring phosphate groups. They are commonly elevated in conditions involving bile duct obstruction.

An enzyme involved in the transfer of gamma-glutamyl residues. It's a sensitive marker for cholestatic liver damage.

Liver damage may result from various causes. AST and ALT levels can help distinguish between specific conditions.

Elevated AST and ALT levels when both exceed 5 times the upper limit of normal, can indicate different types of liver damage.

Significant elevation of AST and ALT, more than 15 times the upper limit of normal, suggests severe liver damage. It can be caused by various factors like viral infection, autoimmune reactions, or drug toxicity.

Elevated AST levels can be caused by a variety of factors, including medication toxicity, ischemic liver damage, and viral infections.

Increased direct bilirubin levels might indicate a blockage in the bile duct, gallstones, liver scarring (cirrhosis), or inflammation of the liver (hepatitis).

Viral hepatitis is the most common liver disease. Detecting it involves testing for various viral antigens, antibodies, and nucleic acids.

Acute viral hepatitis causes significant increases (20-100 times) in liver enzymes (transaminases) initially, followed by a rise in bilirubin levels.

To identify the specific virus causing hepatitis, individuals should be tested for Hepatitis B surface antigen (HBsAg), IgM antibodies to hepatitis B core antigen (anti-HBc IgM), and anti-hepatitis C virus (anti-HVC).

Liver function tests can be normal even when liver disease is present. Normal values do not guarantee the absence of liver disease.

Drugs that can increase ammonia levels in the blood, potentially leading to liver dysfunction. Examples include alcohol, barbiturates, narcotics, and diuretics.

An enzyme specifically elevated in cholestasis, indicating damage to the bile ducts within or outside the liver.

This ratio helps differentiate acute and chronic liver injury. In acute hepatitis, the ALT (alanine aminotransferase) level is higher than the AST (aspartate aminotransferase), while in chronic conditions AST predominates.

A significant increase in ALT levels is seen in conditions like hepatitis, while moderate increases occur in cirrhosis, liver tumors, and obstructive jaundice.

Increased AST levels are usually associated with liver damage and hepatitis.

Elevated ALP levels are characteristic of conditions that hinder bile formation, known as cholestasis.

Increased GGT levels are linked to hepatitis, cirrhosis, liver tumors or metastases, and alcohol-induced liver injury.

Elevated LDH levels are commonly observed in viral hepatitis.