A liver function test (LFT) is a group of blood tests that check how well your liver is working. The results can seem confusing, but understanding the basics helps you have a more informed conversation with your doctor.
ALT and AST (Liver Enzymes)
ALT (Alanine Aminotransferase) and AST (Aspartate Aminotransferase) are enzymes found inside liver cells. When liver cells are damaged or inflamed, these enzymes leak into the blood.
- Mildly elevated (1-3x normal): Common, seen in fatty liver, alcohol, medications. Needs monitoring.
- Moderately elevated (3-10x normal): More significant. Needs investigation for hepatitis, medications, autoimmune disease.
- Highly elevated (>10x normal): Suggests significant liver cell damage. Urgent evaluation needed.
ALT is more specific to the liver. AST is also found in muscle and heart.
ALP and GGT (Cholestatic Markers)
ALP (Alkaline Phosphatase) and GGT (Gamma-glutamyl Transferase) are elevated when there is obstruction to bile flow or bile duct disease.
High ALP + GGT together: Points to bile duct problems (gallstones, bile duct cancer, primary biliary cholangitis).
High GGT alone: Can be caused by alcohol, fatty liver, or certain medications.
Bilirubin
Bilirubin is the yellow pigment that causes jaundice when elevated. It comes from the breakdown of red blood cells and is processed by the liver.
- Elevated bilirubin with elevated liver enzymes: Suggests significant liver cell damage
- Elevated bilirubin with elevated ALP: More likely a blockage in the bile duct
- Isolated mildly elevated bilirubin: Often Gilbert's syndrome -- a harmless genetic variant
Albumin and Prothrombin Time
These tests measure liver function (not just liver damage):
- Albumin: A protein made by the liver. Low albumin indicates reduced liver synthetic function. A sign of chronic or advanced liver disease.
- PT/INR (Prothrombin time): Measures how quickly blood clots. The liver makes clotting factors. Elevated INR means the liver is not keeping up with clotting factor production. Important in assessing severity of liver disease.
Putting It All Together
No single test tells the whole story. Patterns matter:
- Elevated ALT/AST + normal ALP: Hepatitis or liver cell damage
- Elevated ALP/GGT + normal ALT: Bile duct problem
- Low albumin + high bilirubin + elevated INR: Advanced liver failure
Bringing your LFT reports to a liver specialist helps get an accurate interpretation in the context of your full clinical picture.
Abnormal liver tests and unsure what they mean?
Bring your reports to us. We will explain exactly what they mean and what, if anything, needs to be done.