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Liver function test (LFT) is a blood test, where the blood is checked for elevated liver enzymes. It also checks for abnormal levels of protein or substances such as bilIrubin which may indicate abnormal functioning of the liver or liver disease.
When the liver cells undergo damage, they release some enzymes and chemicals into the blood which can be picked up by the blood tests. When the function of the liver is also affected it may not be able to remove waste products such as bilirubin or produce a protein which it normally does. This can also be picked by the blood test called a liver function test (LFT).
As the name indicates, the liver function test gives a gross idea about the normal or abnormal functioning of the liver which may indicate liver health and presence of an underlying disease.
The LFT is often done in the following situations:
• Routine health check-up, to screen for gross liver functioning.
• Assess liver functioning in the presence of risk factors or conditions such as diabetes, fatty liver, high triglycerides, obesity, high blood pressure, or anemia.
• Presence of symptoms of liver disease such as jaundice, dark urine or pale colored stools, upper abdominal pain, or swelling.
• Screening for viral infections of the liver such as hepatitis A, B, and C.
• Alcohol consumers, to check for the condition of the liver.
• To assess the severity of liver dysfunction in cases like fatty liver, hepatitis, or cirrhosis.
• To assess the progression of liver diseases such as hepatitis or cirrhosis.
• To check the effectiveness of treatment.
• Monitor possible side effects of medicines or therapy.
The liver function test (LFT) evaluates the level of liver enzymes, bilirubin, and certain proteins in the blood.
Abnormal levels of these substances in blood may indicate liver problems.
Some of the common liver function tests include:
1. Alanine transaminase (ALT): also known as SGPT, is an enzyme present in the liver that helps to convert proteins into energy. ALT and AST are the most sensitive markers for liver cell injury. They are found to be increased in all types of liver damage. However, they are also present in other organs so the mild increase can be due to damage to other organs also. However, the rise in ALT values is more specific for liver injury than a rise in AST values.
2. Aspartate transaminase (AST): also known as SGOT, is an enzyme that helps to metabolize amino acids. High levels of AST in blood, may get indicate liver or muscle damage. A low level of ALT/AST is not clinically important and can be seen in CKD or vitamin B6 deficiency.
3. Alkaline phosphatase (ALP): is an enzyme that helps to break down protein. High levels of ALP in blood, may indicate an obstruction in bile ducts such as stone or cancer. It may also get increased in certain bone diseases.
4. Gamma-glutamyltransferase (GGT): is an enzyme that helps the liver to metabolize drugs and other toxins. Increased levels may indicate damage to the liver or bile duct.
5. Bilirubin is a waste product present in bile which is produced during the normal breakdown of RBCs. Bilirubin is passed down from the liver into the small intestine through bile ducts. So increased levels of bilirubin may suggest liver damage, abnormal break down of RBCs, or blockage of the bile duct.
6. Total protein and albumin: The liver makes certain proteins such as albumin which perform a number of functions in the body. Reduced levels of albumin and total protein may suggest liver damage or dysfunction.
7. Prothrombin time (PT), is the time taken for your blood to clot on its own and stop bleeding. The liver produces vitamin K and prothrombin, which are helps in the clotting of blood. Liver damage can affect the ability to form these substances which may affect clotting. Thus, increased PT may suggest liver damage.
The LFT alone doesn’t require any fasting. Fasting is required if other tests such as blood glucose test or triglyceride test (which can be done as a part of lipid profile test) are needed to be done along with LFT.
In the absence of these tests, you need not fast before LFT.
Some of the medicines may affect the LFT results which need to be discussed with your doctor.
It is advisable to wear a shirt or a top that has short sleeves or where the sleeves can be rolled up easily to allow easy access for taking blood samples.
It is a very common test that can be done in hospitals, clinics, or labs. Some of the labs also provide facility to collect a blood sample from home. This facility is especially helpful in old people and in people who are chronically sick or bedridden.
• Before collecting a blood sample, a small area of your skin is cleaned by an antiseptic solution to prevent infection from entering your body. The healthcare providers usually choose your elbow pit to draw the blood.
• The person puts a strap on your arm and tightens it to obliterate the veins and make them engorge. During this period you would be asked to close your fist tightly which will further help to engorge the vessels. The engorged vessels allow the lab technician to be easily seen and punctured by the needle.
• The needle is then carefully inserted into the vein of your arm usually the veins of your elbow pit. The needle is attached to a small tube at the other end which collects blood.
• After the desired amount of blood is taken out, the needle is removed and soft pressure is applied with a cotton swab moistened with an antiseptic solution. The puncture site is then covered with a small antiseptic tape to prevent any bleeding or infection.
The test is generally well tolerated by most of the people with usually no significant complications. Only a mild to moderate short-lasting pain is felt to most of the people only at the time of insertion of the needle which doesn’t last once the needle is taken out. There can be a slight discomfort for some people for a short time after the test at the puncture site which doesn’t impair any functioning.
Some of the people may rarely experience following issues after the test:
Fainting: may occur in some people due to a phenomenon called vasovagal syncope. This can be activated in a few people when they see blood in front of their eyes.
Hematoma: A small amount of blood may ooze out under the skin producing a clot or a bruise.
Bleeding: sometimes a small amount of blood may ooze out of the puncture site after taking out the needle or if the area is not covered properly. This can be a problem in people who have issues with the clotting of blood.
Infection: the infection may enter the body in cases where proper antiseptic precautions are not taken such as cleaning the skin before taking blood samples or where the infected needle is used. It is a practice to use the fresh needle which is disposed of with every single use.
Typical normal LFT values are given below:
• Alanine transaminase (ALT)/SGPT: 0 to 45 U/L
• Aspartate transaminase (AST)/SGOT: 0 to 35 U/L
• Alkaline phosphatase (ALP): 30 to 120 U/L
• Gamma-glutamyl transferase (GGT): 0 to 30 U/L
• Bilirubin: 0.2 to 1.7 mg/dL
• Albumin: 40 to 60 g/L
• Prothrombin time (PT): 10.9 to 12.5 seconds
(Note: reference range tends to vary with laboratory. The test results are according to an adult.)
Elevated ALT/AST value up to 300U/L can be non-specific.
Markedly high values above 1000U/L usually suggest diseases like viral hepatitis, toxic or drug-induced liver injury, or ischemic hepatitis.
The elevated value of LFTs is found in 8% of the general population. This increased level of LFTs can be temporary in people with no symptoms, where LFT reports return to the normal value in 30% of these people.
Doctors assess the result of LFTs by interpreting the result of each test and by noting the pattern of elevation. They correlate these results with the signs and symptoms of the person and decide whether to go for more lab tests and imaging investigations.
The following could be the probable causes of abnormal LFT in a person with some specific symptoms or history:
• Alcohol: abnormal LFT with AST generally two times higher than ALT in people who consume a significant amount of alcohol could suggest alcohol-related disease.
• Viral Hepatitis: people living in a country like India, where the viral liver infection is common, raised LFT values especially, with markedly high ALT/AST values(1000U/L) could indicate viral hepatitis.
• Fatty liver and Nonalcoholic Steatohepatitis (NASH): abnormal Liver Function Test results, especially with 1:1 AST to ALT ratio, in people with fatty liver with no history of significant alcohol consumption could indicate NAFLD/NASH. People with risk factors such as overweight, type II diabetes, or dyslipidemia could also show similar results.
• Medicines: people with a frequent or chronic history of intake of medicines such as NSAIDs, drugs for tuberculosis, antibiotics, statins or anti-seizure drugs can develop a high level of liver enzyme. Some herbal remedies and ayurvedic medicines may also cause such effects.
• Autoimmune Hepatitis: abnormal LFT values in young females without any obvious reason could indicate autoimmune hepatitis. These people are further advised to do the following tests: anti-smooth muscle antibody, anti-liver/kidney microsomal antibodies, and antibodies to the liver antigen.
• Hemochromatosis: people with the liver disease having diabetes, and skin hyperpigmentation especially with family history could be considered for evaluation of hemochromatosis. These people are advised for serum ferritin levels and to look for transferrin saturation.
• Wilson Disease: usually young people with abnormal LFT values and KF rings on the eye tests, especially with a family history could indicate Wilson’s disease. Serum ceruloplasmin level and 24-hour urinary copper excretion test is advised in these people.
A specific pattern of an elevated enzyme can also help to suggest a possible cause.
1. If ALT/AST are significantly higher than ALP (alkaline phosphatase), it usually indicates liver cell damage and conditions like viral hepatitis, NASH, alcohol-related liver disease, cirrhosis, ischemic hepatitis, medicine/toxin-induced injury, etc.
Know more about the pattern of the ALT/AST elevation over ALP
Amongst both ALT and AST any one enzyme can be significantly higher than the other.
• If ALT is predominantly high it may indicate: viral hepatitis, steatohepatitis, acute Budd-Chiari syndrome, autoimmune or ischemic hepatitis, hemochromatosis, medications/toxins, Wilson disease,Celiac disease etc.
• If AST is is predominantly high it may indicate: NASH, alcohol-related liver disease, cirrhosis or causes outside liver such as blood break down, thyroid disease, myopathy or exercise)
2. If increased levels of ALP, GGT, and bilirubin are out of proportion to AST/ALT, it usually indicates liver and bile duct diseases such as bile duct obstruction, primary sclerosing cholangitis, primary biliary cirrhosis, medicine induced, hepatic metastasis or conditions such as sarcoidosis, lymphoma, etc.
Some non-hepatic conditions such as bone disease, pregnancy, chronic renal failure, congestive heart failure, or childhood growth may also cause such findings.
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