WHAT IS IT?
A hepatic function panel/liver function tests (LFTs) are a group of lab tests that aim to contextualize the health of the liver by evaluating its functional ability within he body. The components of a standard hepatic function panel are the following blood concentrations.
- Total protein which looks at the amount of protein
- Albumin concentration
- Total bilirubin: the amount of direct and indirect bilirubin
- Indirect bilirubin: this is the amount of unconjugated bilirubin
- Direct bilirubin which is the amount of conjugated bilirubin
- Alkaline phosphatase (ALP): this is an enzyme that is particularly concentrated in the bile duct, liver, kidney, and bone
- Aspartate aminotransferase (AST): this is an enzyme found in the liver, heart,s skeletal muscle, kidneys, brain, and red blood cells.
- Alanine aminotransferase (ALT): this enzyme if principally found in the liver (with negligible amounts found in the kidneys, heart, and skeletal muscle). It is still found in plasma and other body tissues (NOT just the liver).
WHY DO WE DO IT?
This panel is a fairly comprehensive analysis of the liver and can help diagnose conditions that are related to the health of the liver (such as hepatitis, hepatocellular carcinoma, liver cirrhosis, and bile duct obstruction)
HOW IS IT DONE?
This panel is a simple blood test done on a small sample of the patients blood.
WHAT ARE THE REFERENCE VALUES?
Each part of the panel has it’s own reference range (that can vary by the lab doing the exam, or the patient population). The below values are from the USMLE step exam reference ranges.
- Total protein: 6.0-7.8 g/dL
- Albumin: 3.5-5.5 g/dL
- Total bilirubin: 0.1-1.0 mg/dL
- Indirect bilirubin: 0.1-0.8 mg/dL
- Direct bilirubin: 0.0-0.3 mg/dL
- ALP: 20-70 U/L
- AST: 8-20 U/L
- ALT: 8-20 U/L
WHAT DOES IT TELL US?
Each individual test of the panel can offer a piece of insight as to what disease process may be going on
- Decreased total protein may suggest an issue of protein synthesis by the liver
- Decreased albumin concentration can suggest poor production of albumin by the liver
- Elevated total bilirubin warrants further investigation as to what type of albumin is elevated
- Increased indirect bilirubin suggests that the liver may have an issue with conjugating the albumin (or that too much indirect albumin is being created for the liver to process)
- Increased direct bilirubin points to an issue not with the liver conjugating the bilirubin, but the movement of this bilirubin into the bile duct/small intestine.
- Increased ALP can be indicative of bile duct obstruction (or increased active bone formation)
- An increased AST/ALT ratio is suggestive of a disease process that excludes the liver (such as muscle damage)
- An increased ALT/AST ratio is more indicative of a disease process that involves the destruction of liver parenchyma cells.
WHAT CAN’T IT TELL US?
While useful in suggesting that the liver may be involved in a disease process, this test is not specific or diagnostic on its own for any particular disease. It must be used with other tests to ultimately gain a clear diagnosis.
ALP, AST, and ALT are enzymes that are NOT specific to the liver so it is important to realize the limitations of interpreting elevated serum values of these enzymes.
Page Updated: 05.30.2016