Liver function tests are blood tests that help assess the health and functionality of the liver by measuring the levels of various enzymes and substances. Key indicators include Alanine Aminotransferase (ALT), Aspartate Aminotransferase (AST), Alkaline Phosphatase (ALP), Gamma-Glutamyl Transferase (GGT), and bilirubin.
Alanine Aminotransferase (ALT)
Definition: ALT is an enzyme found mainly in the liver. It helps convert alanine, an amino acid, into pyruvate, which is involved in energy production.
Elevated ALT Levels: Elevated ALT levels often indicate liver damage, as the enzyme is released into the bloodstream when liver cells are injured.
Causes of Elevated ALT:
- Viral Hepatitis: Inflammation of the liver caused by hepatitis viruses A, B, C.
- Fatty Liver Disease: Both alcoholic and non-alcoholic.
- Cirrhosis: Scarring of the liver tissue.
- Liver Tumours: Malignant or benign growths.
- Medications and Toxins: Certain drugs, herbal supplements, and toxins.
- Alcohol Abuse: Chronic alcohol consumption.
Normal Range (UK Standards):
- Approximately 7 to 55 units per litre.
Aspartate Aminotransferase (AST)
Definition: AST is an enzyme found in various tissues, including the liver, heart, and muscles. It helps convert aspartate and alpha-ketoglutarate to oxaloacetate and glutamate.
Elevated AST Levels: Elevated AST levels can indicate liver damage, but AST is less specific to the liver than ALT.
Causes of Elevated AST:
- Liver Diseases: Hepatitis, cirrhosis, fatty liver.
- Heart Diseases: Myocardial infarction (heart attack).
- Muscle Disorders: Muscle injury or diseases.
- Alcohol Abuse: Chronic consumption.
Normal Range (UK Standards):
- Approximately 10 to 40 units per litre.
Alkaline Phosphatase (ALP)
Definition: ALP is an enzyme found in many tissues, with high concentrations in the liver, bile ducts, and bone.
Elevated ALP Levels: High ALP levels can indicate liver disease, bile duct obstruction, or bone disorders.
Causes of Elevated ALP:
- Liver Conditions: Cholestasis, liver tumours.
- Bone Disorders: Paget’s disease, osteomalacia.
- Other Conditions: Hyperparathyroidism, pregnancy.
Normal Range (UK Standards):
- Approximately 30 to 130 units per litre.
Gamma-Glutamyl Transferase (GGT)
Definition: GGT is an enzyme found in many organs, but mainly in the liver. It plays a role in the metabolism of glutathione and drug detoxification.
Elevated GGT Levels: High GGT levels typically indicate liver or bile duct issues.
Causes of Elevated GGT:
- Liver Diseases: Hepatitis, cirrhosis.
- Bile Duct Conditions: Cholestasis, bile duct obstruction.
- Alcohol Use: Chronic alcohol consumption.
- Medications: Certain drugs that affect the liver.
Normal Range (UK Standards):
- Approximately 10 to 71 units per litre for males, and 6 to 42 units per litre for females.
Bilirubin
Definition: Bilirubin is a yellow compound formed during the breakdown of haemoglobin from red blood cells. It is processed by the liver and excreted in bile.
Types of Bilirubin:
- Unconjugated (Indirect) Bilirubin: Not water-soluble, formed from haemoglobin breakdown.
- Conjugated (Direct) Bilirubin: Water-soluble, formed in the liver when unconjugated bilirubin is conjugated with glucuronic acid.
Elevated Bilirubin Levels: High bilirubin levels cause jaundice, characterized by yellowing of the skin and eyes.
Causes of Elevated Bilirubin:
- Liver Diseases: Hepatitis, cirrhosis.
- Bile Duct Obstruction: Gallstones, tumours.
- Hemolysis: Increased breakdown of red blood cells.
- Genetic Disorders: Gilbert’s syndrome, Crigler-Najjar syndrome.
Normal Range (UK Standards):
- Total Bilirubin: Approximately 1.2 to 17.0 micromoles per litre.
- Direct Bilirubin: Less than 5.1 micromoles per litre.