Liver enzymes are proteins produced by the liver that play crucial roles in various metabolic processes. They are often measured in blood tests to assess liver function and diagnose liver diseases. The primary liver enzymes include alanine aminotransferase (ALT), aspartate aminotransferase (AST), alkaline phosphatase (ALP), and gamma-glutamyl transferase (GGT).
Common Liver Enzymes Measured in Blood Tests :
- Alanine aminotransferase (ALT)
- Aspartate aminotransferase (AST)
- Alkaline phosphatase (ALP)
- Gamma-glutamyl transferase (GGT)
Key Liver Enzymes
- Alanine Aminotransferase (ALT)
- Function: ALT is an enzyme that helps convert proteins into energy for the liver cells. It is primarily found in the liver.
- Clinical Significance: Elevated levels of ALT often indicate liver damage or inflammation, which can be due to conditions such as hepatitis, fatty liver disease, or cirrhosis.
- Normal Range (UK Standard): 7 to 56 units per litre (U/L).
- Aspartate Aminotransferase (AST)
- Function: AST is an enzyme that helps metabolise amino acids. It is found in various tissues, including the liver, heart, and muscles.
- Clinical Significance: Increased AST levels can indicate liver damage, but because it is also present in other tissues, high levels can also suggest heart or muscle issues.
- Normal Range (UK Standard): 10 to 40 units per litre (U/L).
- Alkaline Phosphatase (ALP)
- Function: ALP is involved in breaking down proteins and is found in high concentrations in the liver, bile ducts, and bone.
- Clinical Significance: Elevated ALP levels can indicate liver disease, bile duct obstruction, or bone disorders.
- Normal Range (UK Standard): 45 to 120 units per litre (U/L).
- Gamma-Glutamyl Transferase (GGT)
- Function: GGT is an enzyme involved in the transfer of amino acids and peptides across the cell membrane. It is found in the liver, bile ducts, and kidneys.
- Clinical Significance: High GGT levels often indicate bile duct problems and liver diseases, such as alcoholic liver disease.
- Normal Range (UK Standard): 5 to 40 units per litre (U/L).
Clinical Uses of Liver Enzyme Tests
- Diagnosis of Liver Conditions
- Hepatitis: Viral hepatitis can cause significantly elevated ALT and AST levels.
- Fatty Liver Disease: Non-alcoholic fatty liver disease (NAFLD) and alcoholic liver disease often show elevated ALT and GGT levels.
- Cirrhosis: Advanced liver disease such as cirrhosis typically results in elevated levels of all liver enzymes, particularly ALT and AST.
- Monitoring Treatment Progress
- Liver enzyme tests are used to monitor the effectiveness of treatments for liver diseases. For example, in patients with hepatitis B or C, decreasing enzyme levels can indicate a positive response to antiviral treatment.
- Screening for Liver Damage
- Routine liver function tests, including enzyme levels, can help detect early liver damage in asymptomatic individuals, especially those at high risk, such as patients with diabetes or a history of heavy alcohol use.
- Assessing Drug Toxicity
- Certain medications can cause liver damage. Regular monitoring of liver enzymes helps in early detection and prevention of drug-induced liver injury.
Interpretation of Results
- Isolated ALT Elevation: Suggestive of liver-specific injury, such as hepatitis.
- ALT and AST Elevation: Indicates more extensive liver damage or inflammation.
- ALP Elevation: May indicate bile duct obstruction or bone disease.
- GGT Elevation: Often used to confirm that the ALP elevation is due to liver disease rather than bone disease.