Medical Reports
Liver Function Test (LFT) Explained: ALT, AST, ALP, and Bilirubin Normal Ranges
Learn how to read your Liver Function Test (LFT) report. Understand high ALT, AST, ALP, and bilirubin values and what they mean for liver health.
Key takeaways
- A Liver Function Test (LFT) measures key enzymes (ALT, AST, ALP) and proteins/pigments (Bilirubin, Albumin) in your blood.
- ALT (Alanine Aminotransferase) is the most specific marker for liver cell inflammation.
- Slight elevations in LFT markers are common and can be triggered by medications, intense exercise, or fatty liver changes.
Core Liver Enzymes: ALT, AST, and ALP
Liver Function Tests measure enzymes that leak into the bloodstream when liver cells are stressed or damaged. Understanding the ratio between ALT and AST gives clinicians important diagnostic clues.
To quickly translate complex laboratory markers into plain language, try our free medical report summary tool.
- •ALT (Alanine Aminotransferase): Normal 7-56 U/L. Found primarily in liver cells; elevated ALT signals active liver inflammation.
- •AST (Aspartate Aminotransferase): Normal 10-40 U/L. Present in liver, heart, and muscle tissue; elevated AST along with ALT confirms hepatic involvement.
- •ALP (Alkaline Phosphatase): Normal 44-147 U/L. Related to bile ducts; elevated ALP can indicate gallbladder or bile duct obstruction.
Bilirubin, Albumin, and Total Protein
In addition to enzymes, LFTs measure substances produced or cleared by the liver to assess overall liver synthetic function.
- •Total Bilirubin: Normal 0.1-1.2 mg/dL. A yellow pigment produced during red blood cell breakdown; high levels cause jaundice.
- •Direct (Conjugated) Bilirubin: Measures processed bilirubin ready for excretion via bile.
- •Albumin: Main protein synthesized by the liver; low albumin indicates chronic liver dysfunction or nutritional deficiency.
Common Reasons for Abnormal Liver Results
An abnormal LFT result does not automatically mean severe liver disease. Non-alcoholic fatty liver (MASLD/NAFLD), alcohol consumption, prescription medications (statins, acetaminophen), and recent intense weightlifting can temporarily raise enzyme levels.
- •Fatty Liver: Most common cause of mild ALT/AST elevation in adults.
- •Medications & Supplements: Herbal supplements and pain relievers can strain liver enzymes.
- •Follow-Up Testing: Ultrasound or repeat blood draw in 4-8 weeks is standard clinical practice.
Common questions
What is a dangerous ALT level?
Normal ALT is under 56 U/L. Mild elevation (up to 100-200 U/L) is often caused by fatty liver or meds. Extremely high levels (over 1,000 U/L) require urgent medical evaluation for acute liver injury.
Can exercise cause elevated AST and ALT?
Yes, strenuous muscle exercise or heavy weightlifting within 48 hours of testing can cause temporary AST and ALT increases due to muscle tissue micro-tears.