Liver Function Tests (LFTs): A Comprehensive Overview

Introduction

The liver performs many essential roles, including metabolism, detoxification, protein synthesis, and bile production. Healthcare providers rely on Liver Function Tests (LFTs) to evaluate liver health, detect disease, monitor conditions, and assess medication impact.

Understanding Liver Function Tests

LFTs measure enzymes, proteins, and substances in the blood that reflect liver performance. These tests help doctors:

• Diagnose liver diseases
• Track disease progression
• Evaluate treatment success
• Detect medication side effects

Key Components of LFTs

Alanine Aminotransferase (ALT)

• ALT primarily resides in the liver and supports amino acid metabolism.
• Elevated ALT levels often indicate liver cell injury, especially in hepatitis.

Aspartate Aminotransferase (AST)

• AST exists in the liver, heart, muscles, and other tissues.
• High AST levels may signal liver or muscle damage.

Alkaline Phosphatase (ALP)

• ALP works in the bile ducts and bones.
• Increased ALP levels often reflect bile duct obstruction or liver disease.

Gamma-Glutamyl Transferase (GGT)

• GGT helps with glutathione metabolism and exists in the liver and bile ducts.
• Elevated GGT levels can indicate bile duct issues or alcohol-related liver damage.

Bilirubin

• The liver processes bilirubin, a byproduct of red blood cell breakdown.
• High bilirubin levels can cause jaundice and may signal impaired liver function.

Albumin

• The liver produces albumin, which maintains fluid balance and transports substances.
• Low albumin levels often suggest chronic liver disease or malnutrition.

Prothrombin Time (PT) and International Normalized Ratio (INR)

• The liver produces clotting factors that influence PT and INR.
• A prolonged PT or high INR can indicate impaired liver synthetic function.

Interpreting LFT Results

Doctors interpret LFTs based on the pattern of abnormal values:

• A hepatocellular pattern shows high ALT and AST levels, indicating liver cell injury.
• A cholestatic pattern reveals high ALP and GGT levels, suggesting bile duct issues.
• A mixed pattern presents elevations in both sets of enzymes, pointing to combined problems.

Doctors consider the degree of elevation and use clinical findings and other tests to support interpretation.

Common Causes of Abnormal LFTs

• Viral hepatitis (A, B, C)
• Alcoholic liver disease
• Non-alcoholic fatty liver disease (NAFLD)
• Drug-induced liver injury
• Autoimmune hepatitis
• Bile duct obstruction (e.g., gallstones)

Limitations of LFTs

LFTs provide essential information, but they have limits:

• They don’t always identify the exact cause.
• Temporary elevations can result from medications or physical activity.
• Normal LFTs don’t always rule out liver disease.

Doctors use LFTs alongside other tests and patient histories to form accurate diagnoses.

Additional Diagnostic Tools

When LFTs show abnormalities, healthcare providers may:

• Order imaging tests like ultrasound, CT scan, or MRI
• Perform a liver biopsy to examine tissue
• Use serological tests to detect infections or autoimmune conditions

Monitoring Liver Health

Doctors regularly check LFTs to:

• Track chronic liver disease progression
• Watch for side effects of medications
• Evaluate liver readiness before surgery

Conclusion

Liver Function Tests allow doctors to evaluate liver health, detect disease, and guide treatments. By understanding these tests and using them in clinical practice, healthcare professionals can make informed decisions and offer effective care for patients with liver-related conditions.