Liver Function Tests

Liver function tests are done on a patient's serum or plasma sample, procured by phlebotomy, by a medical technologist. This clinical biochemistry laboratory blood analysis furnishes crucial data regarding the condition of the patient's liver. A hepatic function panel is a blood test wherein low or high levels may point to liver diseases or damage. This panel measures the blood levels of protein albumin, bilirubin and liver enzymes.

Albumin measurement
Albumin is the major constituent of the total protein in the liver. The remnant is called globulin. Albumin must be present as 3.9 to 5.0 g/dL. In chronic liver diseases like "cirrhosis" or "nephrotic syndrome" the level is decreased. Poor nutrition or protein catabolism may cause "hypoalbuminaemia".

Aspartate transaminase : AST
This is also called "serum glutamic oxaloacetic transaminase" or "aspartate aminotransferase". This enzyme is related to liver parenchymal cells. It's level must be 10 to 34 IU/L. This level is raised if there is acute liver damage.

Alanine transaminase : ALT
This is also called "serum glutamic pyruvic transaminase" or "alanine aminotransferase". This enzyme is present in liver cells (hepatocytes). It's level must be 8 to 37 IU/L. This level rises in case of acute liver damage like "viral hepatitis" or "paracetamol overdose".

The ratio of AST to ALT is used to differentiate between the reasons of liver damage.

Alkaline phosphatase : ALP
This is an enzyme that is present in the cells lining the biliary ducts of the liver. If the range is 44 to 147 IU/L, it is normal. This level rises in case of infiltrative diseases of the liver, intrahepatic cholestasis or large bile duct obstruction.

Gamma glutamyl transpeptidase : GGT
This is a more sensitive marker for cholestatic damage than ALP and is very specific to the liver. The standard range is 0 to 51 IU/L. Even very petty and sub-clinical levels of liver dysfunction can cause a rise in this range. Both acute and chronic alcohol toxicity raise GGT. The reason of an isolated elevation in ALP can be detected by GGT.

Total bilirubin : TBIL
An increase in the total bilirubin can lead to jaundice.

• Hepatic problems are caused due to deficiencies in bilirubin metabolism due to "cirrhosis" or "viral hepatitis".
• Prehepatic problems are caused due to "hemolytic anemias" or "internal hemorrhage". There is an increased bilirubin production.
• Posthepatic problems are caused due to obstruction of the bile ducts. There is a deficiency in bilirubin excretion.

Direct bilirubin

• When direct bilirubin is normal, then the unconjugated bilirubin may be problematic : viral hepatitis, cirrhosis or hemolysis may be present
• When direct bilirubin is elevated, then the excretion of bilirubin may be problematic : cancer or bile duct obstruction by gallstones may be present

Prothrombin time test : PTT
Liver cell damage and bile flow obstruction both effect proper blood clotting. The time taken by the blood to clot is measured by this test.

Alpha-fetoprotein test
The fetal liver and testes generate this protein. It is a symptom of hepatitis or cancer.

Mitochondrial Antibodies test
If such antibodies are present, they prove the existence of chronic active hepatitis, primary biliary cirrhosis or other autoimmune disorders.

Other liver function tests

• Increased level of Lactate dehydrogenase possibly means liver damage
• Ability to produce glucose is the final function that is lost during exploding liver failure
• 5' nucleotidase is a substitute for GGT to confirm if an elevated ALP has a biliary or extra-biliary origin
• the International normalized ratio if increased indicates that the synthesis of vitamin-K dependent coagulation factors has been affected and the blood will take more time to clot. This is vital is the patient is to be operated.

Liver functions

• generating nearly 80% cholesterol
• maintaining correct quantity of glucose
• producing urea
• transforming glucose to glycogen
• producing some amino acids that are the building blocks of proteins
• producing substances that break down fats
• filtering alcohol from the blood
• storing vitamins and minerals

When these functions are affected by some liver problems, the following common symptoms may be seen:

• jaundice
• liver enlargement
• ascites
• cholestasis
• portal hypertension
• liver encephalopathy
• liver failure