Human body has several vital organs and liver is one of the most important among them. Its essential function is to destroy toxins circulating in the body, produce and store bile and take part in hundreds of biochemical reactions and metabolic processes. Several types of blood tests are carried out to determine irregularity in liver function.
These tests are called liver function test (LFT). The test is performed to measure proteins, enzymes and bilirubin (metabolic waste) in the blood. It helps in evaluating the extent of liver damage and thus LFT is used as a marker in diagnosis, monitoring and treatment of a liver disease.
What Is The Purpose Of Liver Function Tests?
Liver function test is an important marker for determining whether your liver is healthy or diseased. This test measures level of protein, enzymes and waste such as bilirubin in blood. Some tests such as ALT and AST measure enzymes that are released in large amount due to liver disease.
Tests like serum protein helps to know how well liver is taking part in production of albumin and globulin, types of protein. This test is also indicated how well liver is able to metabolize waste product bilirubin in the blood.Doctors often recommend LFT in following situations when they suspect liver damage or deviation in its function.
- For screening hepatitis when a person has jaundice, loss of appetite, pain in right upper abdomen and several other symptoms that are suspected to be due to hepatitis A, B or C.
- For monitoring liver function when certain drugs are prescribed are known to cause liver toxicity. For example, LFT is done frequently when a patient is taking anti tuberculosis medicines.
- Monitors the effect of treatment on liver in case of liver diseases.
- Helps to evaluate the severity of disease, especially in liver diseases such as cirrhosis.
Liver Function Tests And Interpretation Of Results
Liver function test most commonly done and most useful in the diagnosis of liver diseases are given below:
- Serum bilirubin test: Bilirubin is a waste product formed due to breakdown of red blood cells and hemoglobin in the blood. Liver processes it before it is excreted out through stool. When liver is damaged, it is unable to completely process bilirubin. As a result there is back up of this waste product in the blood. Thus bilirubin is high when there is deterioration in liver function. Normal total bilirubin level is 0.3-1.0 mg/dl. The level is markedly raised in viral hepatitis, alcoholic hepatitis, etc.
- Serum enzyme tests: These tests usually help to diagnose the type of liver damage, whether cellular damage or cholestatic (pertaining to excretion of bile). There are two types of enzyme tests namely AST (SGOT) and ALT (SGPT).
- Aspartate aminotransferase (AST or SGOT): It is an enzyme present in parts of body such as heart, liver and muscles. Damage to any of these organs can elevate the level of AST. The result of the test is therefore evaluated with ALT test when it comes to diagnosis of liver disease. Normal value of AST is 5-40 IU/L.
- Alanine aminotransferase (ALT or SGPT): This enzyme is used by the liver to metabolize protein. When liver is damaged too much of ALT is discharged in the blood leading to its elevation in blood. High ALT is found in viral hepatitis, alcoholic liver damage, cirrhosis, and hepatic metastasis. Normal value of ALT is 5-35 IU/L.
- Alkaline phosphatase (ALP) test: This is a plasma membrane enzyme found in liver, bones, intestine and bile duct. Transient elevation can occur in all types of liver ailments, but most striking rise is seen in obstruction of bile duct. It is also raised in primary and secondary hepatic tumor. This enzyme is also raised in bone diseases, liver abscess, certain types of malignancies etc. Normal value of serum alkaline phosphatase is 30-120 IU/L.
- Serum protein: Albumin and globulin are two main proteins prepare by the liver. Serum albumin is essential for prevention of leakage of fluid from the blood vessels. It also helps to carry vitamins, hormones and other substances throughout the body. Low serum albumin indicates that your liver is not working properly. Normal value of serum albumin is 3.5-5.0 g/dl. Normal value of globulin is 2.0-3.5g/dl.