What is the difference between Gamma-Glutamyl Transferase (GGT), Serum Glutamic-Pyruvic Transaminase (SGPT) or Alanine Transaminase (ALT), and Serum Glutamic-Oxaloacetic Transaminase (SGOT) or Aspartate Transaminase (AST)?

Differences Between GGT, SGPT (ALT), and SGOT (AST)

GGT, SGPT (ALT), and SGOT (AST) are distinct liver enzymes with different cellular locations, tissue distributions, and clinical significance in diagnosing and monitoring liver diseases.

Enzyme Characteristics and Locations

• Gamma-Glutamyl Transferase (GGT):

  • Located primarily on plasma membranes of most cells and organ tissues, particularly hepatocytes 1
  • Primary role is extracellular catabolism of glutathione, playing an important role in cellular defense against oxidative stress 1
  • Present in liver, kidney, pancreas, and other tissues, but serum elevation is most specific for liver and biliary tract disease 2

• Serum Glutamic-Pyruvic Transaminase (SGPT/ALT):

  • Now commonly called Alanine Aminotransferase (ALT) 3
  • Primarily found in the liver cytosol with low concentrations in skeletal muscle and kidney 3
  • More specific for liver injury than AST due to its predominantly hepatic distribution 3
  • Normal levels are 29-33 IU/L in men and 19-25 IU/L in women 3

• Serum Glutamic-Oxaloacetic Transaminase (SGOT/AST):

  • Now commonly called Aspartate Aminotransferase (AST) 3
  • Found in both cytosolic and mitochondrial forms 4
  • Present in liver, heart, skeletal muscle, kidneys, brain, and red blood cells 3
  • Less specific for liver injury than ALT due to its wider tissue distribution 3

Clinical Significance and Interpretation

• GGT Elevation:

  • Highly sensitive for liver disease but less specific than other enzymes 3
  • Elevated in approximately 75% of habitual alcohol drinkers, making it useful for monitoring alcohol abstinence 3
  • May indicate liver injury even when other enzymes are only mildly elevated 5
  • Useful in identifying cholestatic liver diseases 3
  • Can be elevated due to non-alcoholic liver disease, obesity, diabetes, smoking, or drug use 3

• ALT (SGPT) Elevation:

  • Most specific indicator of hepatocellular damage 3
  • Elevations specifically reflect liver injury due to its predominantly hepatic distribution 3
  • Can be classified as mild (<5× upper limit), moderate (5-10× upper limit), or severe (>10× upper limit) 3
  • May be mildly elevated in muscle disorders, though this is less common than with AST 6

• AST (SGOT) Elevation:

  • Less specific for liver disease due to its presence in multiple tissues 3
  • Can be elevated in disorders involving heart, skeletal muscle, kidneys, brain, and red blood cells 3
  • Often elevated concomitantly with ALT in liver diseases 3
  • May be elevated in muscle disorders even without liver involvement 6

Diagnostic Patterns and Ratios

• AST/ALT Ratio:

  • Ratio >2 suggests alcoholic liver disease 3
  • Ratio >3 has a very high probability of indicating alcoholic hepatitis 3
  • Elevated ratio also seen in advanced fibrosis and cirrhosis regardless of cause 5
  • In liver cirrhosis, the increased ratio is due to greater decrease in liver cytosol GPT (ALT) activity 4

• Patterns in Specific Liver Diseases:

  • Alcoholic Liver Disease: AST typically higher than ALT, GGT markedly elevated 3
  • Viral Hepatitis: ALT typically higher than AST 3
  • Non-alcoholic Fatty Liver Disease: Mild to moderate elevations of both enzymes 5
  • Cholestatic Disease: Elevated GGT with or without elevated alkaline phosphatase 5
  • Hepatocellular Injury: Predominantly elevated AST and ALT 5

Clinical Applications

• Screening and Diagnosis:

  • GGT, ALT, and AST are commonly used for early detection of liver disease 3
  • ALT levels >500 U/L and AST levels >300 U/L suggest significant hepatic injury 7
  • GGT elevation may persist even when other liver enzymes normalize 3

• Monitoring:

  • GGT recovers slowly following abstinence from alcohol, making it useful for monitoring compliance 3
  • Regular monitoring of these enzymes every 3-6 months is recommended for patients with liver disease 5
  • More frequent monitoring is needed for patients with advanced liver disease 5

• Special Considerations:

  • Baseline testing of AST and ALT is indicated for patients with HIV infection, pregnant women, those with chronic liver disease, and regular alcohol users 3
  • Some experts recommend withholding certain medications if transaminases exceed three times the upper limit of normal with symptoms or five times without symptoms 3

Remember that while these enzymes are valuable diagnostic tools, they should be interpreted in the context of the patient's clinical presentation, other laboratory findings, and imaging studies for accurate diagnosis and management of liver diseases.