What are the normal ranges for liver function tests, including Alanine Transaminase (ALT), Aspartate Transaminase (AST), Alkaline Phosphatase (ALP), total bilirubin, and albumin?

Normal Laboratory Value Ranges for Liver Function Tests

The normal reference ranges for liver function tests include ALT (0-40 U/L), AST (0-40 U/L), ALP (40-120 U/L), total bilirubin (0.1-1.2 mg/dL), and albumin (3.5-5.0 g/dL), though these may vary slightly between laboratories. 1

Key Liver Function Test Reference Ranges

Hepatocellular Enzymes

• Alanine Transaminase (ALT)

  • Normal range: 0-40 U/L
  • ULN (Upper Limit of Normal): ~40-45 U/L in most central laboratories 2
  • Gender differences: Males typically have higher values than females

• Aspartate Transaminase (AST)

  • Normal range: 0-40 U/L
  • Typically lower than ALT in healthy individuals
  • AST:ALT ratio >2 suggests alcoholic liver disease, while ratio <1 suggests metabolic-related fatty liver 1

Cholestatic Markers

• Alkaline Phosphatase (ALP)

  • Normal range: 40-120 U/L
  • Age variations: Higher in children and elderly
  • Typically <2× ULN even in mild liver disease 2

• Gamma-Glutamyl Transferase (GGT)

  • Normal range: 0-50 U/L
  • Used to confirm hepatobiliary origin of elevated ALP 1
  • May range between normal and >400 U/L in NAFLD patients 2

Synthetic Function

• Albumin

  • Normal range: 3.5-5.0 g/dL
  • Decreases with age 1
  • Reflects liver's synthetic capacity

• Total Protein

  • Normal range: 6.0-8.0 g/dL
  • Regional variations exist 1

Excretory Function

• Total Bilirubin
  • Normal range: 0.1-1.2 mg/dL
  • Gender differences: Males typically have higher values 1
  • Usually normal until advanced stages of liver disease 2

Important Considerations for Interpretation

Laboratory Variability

• Reference ranges may vary significantly between different laboratories due to differences in reference populations and analytical variation among commercial assays 2, 1
• Always refer to the specific reference ranges provided by the testing laboratory

Classification of Liver Enzyme Elevations

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

Clinical Context

• The magnitude of liver enzyme elevation does not necessarily correlate with clinical significance or prognosis 1
• The clinical context and specific analyte that is abnormal are more important than the degree of elevation 1
• Patients with significant liver fibrosis may have liver enzymes within normal reference ranges 1

Patterns of Abnormalities

• Hepatocellular pattern: Predominant elevation of ALT and AST
• Cholestatic pattern: Predominant elevation of ALP and GGT
• Mixed pattern: Elevation of both transaminases and cholestatic enzymes

Monitoring and Management

• For mild elevations (ALT <5× ULN), repeat testing in 2-5 days with follow-up for symptoms 1
• For severe elevations (ALT ≥8× ULN), consider interrupting suspected medications and implement close monitoring 1
• For ALT ≥3× ULN with total bilirubin ≥2× ULN, immediate intervention is advised 1

Remember that liver function tests should be interpreted in the context of the patient's clinical presentation, medical history, and other laboratory findings. Isolated abnormalities often require repeat testing before extensive workup is initiated.