Introduction
Liver function tests (LFTs) are essential tools for diagnosing and managing liver diseases. Understanding how to interpret these tests is crucial for healthcare professionals, especially in pediatrics. In this guide, we’ll break down the key components of LFTs, common abnormalities, and their clinical relevance in 5 easy steps.
Step 1: Know the Components of Liver Function Tests
Liver function tests evaluate different aspects of liver health. Key components include:
Alanine Transaminase (ALT) – Reflects hepatocyte injury.
Aspartate Transaminase (AST) – Indicates liver or muscle damage.
Alkaline Phosphatase (ALP) – Elevated in bile duct or bone disorders.
Gamma-Glutamyl Transferase (GGT) – Confirms biliary origin of ALP elevation.
Bilirubin (Total and Direct) – Assesses liver’s excretory function.
Albumin and Total Protein – Indicates synthetic function.
Prothrombin Time (PT) – Evaluates liver’s ability to produce clotting factors.
Pro Tip: Focus on ALT and AST for hepatocellular damage and ALP for cholestasis.
Step 2: Understand Normal Ranges
Here are the normal values for LFT components:
ALT: 7-56 U/L
AST: 10-40 U/L
ALP: 40-130 U/L
Bilirubin (Total): 0.1-1.2 mg/dL
Albumin: 3.5-5.0 g/dL
Clinical Insight: Values can vary based on age, sex, and laboratory methods, especially in children.
Step 3: Recognize Patterns in Liver Function Test Abnormalities
- Hepatocellular Injury
High ALT and AST levels.
Common in viral hepatitis and drug-induced liver injury.
- Cholestatic Patterns
Elevated ALP and GGT.
Seen in bile duct obstruction or primary biliary cholangitis.
- Synthetic Dysfunction
Low albumin and prolonged PT.
Indicates advanced liver disease or cirrhosis.
Step 4: Correlate with Clinical Presentation
Interpretation of LFTs should always align with clinical findings. For example:
Jaundice: Elevated bilirubin levels.
Right Upper Quadrant Pain: Check ALP and GGT for bile duct issues.
Fatigue: Low albumin might suggest chronic liver disease.
Step 5: Follow-Up Tests for Abnormal LFTs
When LFTs are abnormal, additional tests are required:
Ultrasound Abdomen – Identifies structural abnormalities.
Viral Hepatitis Panel – Screens for hepatitis A, B, and C.
Autoimmune Markers – ANA and anti-smooth muscle antibodies.
Liver Biopsy – For definitive diagnosis in unexplained cases.
Common Scenarios in Pediatrics
Neonatal Jaundice: Isolated high bilirubin with normal ALT/AST.
Viral Hepatitis: Elevated ALT and AST with symptoms of fever and malaise.
Biliary Atresia: High bilirubin and ALP with pale stools.
Conclusion
Interpreting liver function tests requires a systematic approach that combines understanding of test components, normal ranges, and clinical context. By mastering these 5 steps, you can improve your diagnostic accuracy and patient care.
