Hepatic Module
Clinical Tests
Learning Objectives
By the end of this section, you will be able to:
- Describe the basis of common laboratory tests associated with liver function
Liver Function Tests
As you read through the following tests, consider what information or insights the test result could offer with regards to a patient’s liver health or disease. For an overview, please see HealthLink – Liver Function Tests for details.
Serum Albumin
One of liver’s key function is protein synthesis. Albumin is made by hepatocytes and is normally secreted into the blood.
See HealthLink – Total Serum Protein for more details.
Prothrombin Time and INR
Hepatocytes synthesize clotting factors (proteins). Prothrombin time measures how long it takes blood to clot; the test result is often reported as INR (international normalized ratio).
See HealthLink – Prothrombin Time and INR for more details.
It is important to note that hepatocytes synthesize a lot of proteins, including many enzymes. Some of these enzymes normally remain within hepatocytes. If there is hepatocyte damage or death, then the serum concentration of these enzymes would increase.
Bilirubin
Bilirubin circulates as conjugated and unconjugated bilirubin in the blood. The levels of conjugated and unconjugated bilirubin give insights into the types of liver disease and causes of jaundice (pre-hepatic, hepatocellular, post-hepatic).
Total serum bilirubin = conjugated bilirubin + unconjugated bilirubin
Given conjugated bilirubin’s water solubility, it could also be detected in urine when serum conjugated bilirubin is high.
See HealthLink – Bilirubin for more details.
Urobilinogen
Only small amounts of urobilinogen are found in urine. Urobilinogen in urine can be a sign of liver disease; lower than normal urobilinogen suggests that there is a decrease in conjugated bilirubin making its way into or through bile ducts.
Aspartate Aminotransferase (AST)
This is widely used to assess hepatocellular damange. Aspartate aminotransferase is made in almost all tissues, with the highest amounts being made in the heart, liver, and skeletal muscles. Therefore, AST is not very “liver-specific”. In the liver, AST is normally in the cytoplasm of hepatocytes.
See HealthLink – Aspartate Aminotransferase (AST) for more details.
Alanine Aminotrasferase (ALT)
This is widely used to assess hepatocellular damange. Alanine aminotransferase is made highest amounts in hepatocytes, with small amounts being produced in kidney, heart, pancreas, and muscles. Therefore, ALT is more “liver-specific” than AST. ALT is normally in the cytoplasm of hepatocytes.
See HealthLink – Alanine Aminotransferase (ALT) for more details.
Alkaline Phosphatase (ALP)
Alkaline phosphatase is an enzyme present in the cells lining the biliary ducts but also in bone. It is often used to detect hepatocellular damage, biliary obstruction, or bone disease.
A great increase in ALP activity (10x) could indicate biliary obstruction (e.g., gallstone blocking the bile duct).
See HealthLink – Alkaline Phosphatase for more details.
γ-Glutamyltransferase (GGT)
γ-Glutamyltransferase is an enzyme mainly found in the liver, bile ducts, and kidney cells. It can indicate liver or renal issues. It is not specific for any type of liver disease, but is frequently the first abnormal liver function test demonstrated in serum of heavy drinkers. It can also be highly elevated in biliary obstructions, which can be useful to confirm whether ALP results are from bone disease.