What are the normal lab value ranges in a Liver Function Test, including Alanine Transaminase (ALT), Aspartate Transaminase (AST), Alkaline Phosphatase (ALP), Gamma-Glutamyl Transferase (GGT), total bilirubin, direct bilirubin, and albumin?

Normal Lab Value Ranges in a Liver Function Test

The normal reference intervals for liver function tests include ALT (<5× ULN), AST (<5× ULN), ALP (130-831 U/L), GGT (10-28.2 U/L for infants, 30.6-160.7 U/L for newborns), total bilirubin (<1.37 mg/dL), direct bilirubin (<0.41 mg/dL), and albumin (3.88-5.82 g/dL). 1

Standard Liver Function Test Components and Reference Ranges

Hepatocellular Markers

• Alanine Transaminase (ALT)

  • Normal range: Typically <5× upper limit of normal (ULN) 1
  • Mild elevation: <5× ULN
  • Moderate elevation: 5-10× ULN
  • Severe elevation: >10× ULN

• Aspartate Transaminase (AST)

  • Normal range: Typically <5× ULN 1
  • Mild elevation: <5× ULN
  • Moderate elevation: 5-10× ULN
  • Severe elevation: >10× ULN

Cholestatic Markers

• Alkaline Phosphatase (ALP)

  • Normal range: 130-831 U/L 2
  • Typically <10× ULN in primary biliary cholangitis 3

• Gamma-Glutamyl Transferase (GGT)

  • Normal range for infants: 10-28.2 U/L 2
  • Normal range for newborns: 30.6-160.7 U/L 2
  • Important for confirming hepatobiliary origin of elevated ALP 3

Synthetic Function Markers

• Total Protein

  • Normal range: Varies by region 1

• Albumin

  • Normal range: 3.88-5.82 g/dL 2
  • May vary by age 1

Excretory Function Markers

• Total Bilirubin

  • Normal range: <1.37 mg/dL 2
  • May vary by gender 1

• Direct Bilirubin (Conjugated)

  • Normal range: <0.41 mg/dL 2

Interpretation of Liver Function Tests

Pattern Recognition

• Hepatocellular Pattern: Predominant elevation of transaminases (ALT, AST)

  • AST:ALT ratio >2 suggests alcoholic liver disease 1
  • AST:ALT ratio <1 suggests metabolic-related fatty liver 1

• Cholestatic Pattern: Predominant elevation of ALP and GGT

  • In malignant biliary strictures, ALP elevation (4.3× ULN) typically exceeds AST elevation (2.6× ULN) 4
  • In obstructive stone disease, AST elevation may equal or exceed ALP elevation 4

• Mixed Pattern: Elevations in both transaminases and cholestatic markers

Special Considerations

• Laboratory reference ranges for liver enzymes may vary significantly between facilities 3
• GGT is particularly useful for confirming the hepatobiliary origin of elevated ALP 3
• Elevated GGT (>95.5 U/L) combined with elevated ALP (>151.5 U/L) has 93.5% sensitivity and 85.1% specificity for asymptomatic choledocholithiasis 5

Clinical Context for Interpreting Results

• The magnitude of liver enzyme elevation does not necessarily correlate with clinical significance or prognosis 3
• The clinical context and specific analyte that is abnormal are more important than the degree of elevation 3
• Patients with significant liver fibrosis may have liver enzymes within normal reference ranges 3
• Common causes of elevated liver enzymes include:
  • Nonalcoholic fatty liver disease (NAFLD): Most common cause in developed countries 1
  • Alcoholic liver disease
  • Drug-induced liver injury
  • Viral hepatitis
  • Autoimmune hepatitis 1

Monitoring Recommendations

• For mild elevations: Repeat testing in 2-5 days with follow-up for symptoms 3
• For severe elevations (ALT ≥8× ULN): Consider interrupting suspected medications and close monitoring 3
• For ALT ≥3× ULN with total bilirubin ≥2× ULN: Immediate intervention required 3
• Monitor liver enzymes every 2-4 weeks until normalization 1

Remember that reference intervals may differ based on age, gender, and geographical region. Always interpret liver function tests in the context of the patient's clinical presentation and risk factors for liver disease.