What are the normal ranges for hepatic function tests?

Normal Ranges for Hepatic Function Tests

In general clinical practice, hepatic function is considered within normal range when aminotransferases (ALT/AST) are <1× upper limit of normal (ULN), alkaline phosphatase is <1× ULN, total bilirubin is ≤1× ULN, albumin is normal, and INR/PT is normal. 1, 2

Standard Reference Ranges by Test

Aminotransferases (ALT/AST)

• ALT upper reference ranges: 35-79 U/L for men, 31-55 U/L for women, though these vary significantly by laboratory 3
• Normal range defined as: <1× ULN for both ALT and AST 3
• Clinical significance threshold: Elevations become clinically concerning at ≥2× ULN, with severe elevations defined as >10× ULN 2
• Important caveat: AST can be elevated from muscle injury; creatine kinase should be checked to differentiate hepatic from muscular origin 2

Alkaline Phosphatase (ALP)

• Normal range: <1× ULN 3
• Critical consideration: ALP may originate from bone rather than liver, particularly in post-menopausal women with osteoporosis 3
• Confirmation required: Elevated ALP should be confirmed as hepatobiliary in origin using GGT and/or ALP isoenzyme fractionation 3
• Age-related changes: ALP increases by 20% between the 3rd and 8th decade of life 3

Bilirubin

• Normal range: Total bilirubin ≤1× ULN 3
• Exception: Gilbert's Syndrome or hemolysis may cause isolated hyperbilirubinemia without liver dysfunction 3
• Gender and ethnic variations: Total bilirubin shows significant racial/ethnic differences in distribution 3

Synthetic Function Markers

• Albumin: Should be within normal laboratory range 1, 2
• INR/Prothrombin time: Should be normal and correctable with vitamin K if prolonged 3
• Clinical significance: Normal albumin and INR indicate preserved synthetic liver function, even if enzymes are mildly abnormal 1

Context-Specific Thresholds

Clinical Trial Eligibility (Non-Cirrhotic Patients)

For patients without advanced cirrhosis participating in clinical trials, consensus guidelines define acceptable ranges as: 3

• Aminotransferases: <5× ULN
• Alkaline phosphatase: <10× ULN (upper threshold)
• Total bilirubin: <1× ULN (excluding Gilbert's Syndrome)

Chronic Hepatitis B Monitoring

• Inactive carriers: Normal ALT with HBV DNA <2000 IU/ml 3
• Liver stiffness measurement: <5-6 kPa indicates absent or minimal fibrosis 3
• Interpretation caution: Liver stiffness should not be used in patients with very high ALT levels (>10× ULN) 3

Important Laboratory Variability Considerations

Population-Based Differences

• Racial/ethnic variations: Among 38 standard laboratory tests, only five (glucose, phosphorus, potassium, total bilirubin, uric acid) did not show significant racial/ethnic differences 3
• Example: Serum creatinine normal range for White females is 0.50-1.10 mg/dL, but 0.43-0.88 mg/dL for Asian females 3
• Gender differences: Significant variations exist for ALT, total bilirubin, cholesterol, bicarbonate, calcium, and total protein 3

Age-Related Changes

• Creatinine clearance: Increases by 10 mL/min/1.73 m² per decade 3
• Postprandial glucose: Increases by 30-40 mg/dL per decade after age 40 3
• Platelet count: Decreases by approximately 20,000/mcl between the sixth and eighth decades 3

Clinical Pitfalls to Avoid

Don't assume all elevated ALP is hepatic: Always confirm hepatobiliary origin with GGT or isoenzyme fractionation, especially in post-menopausal women or patients with bone disease 3, 4

Don't overlook muscle sources of AST elevation: Check creatine kinase when AST is disproportionately elevated compared to ALT 2

Don't use single measurements as definitive: Laboratory values fluctuate, particularly in patients with underlying liver disease; repeat testing establishes true baseline 2

Don't ignore laboratory-specific reference ranges: ULN varies among laboratories and by sex and age groups; absolute values should be reported alongside multiples of ULN 3