Blood tests used to help diagnose and monitor liver damage or disease are called liver function tests. They measure the level of proteins and enzymes in the blood and assess the general state of the liver or biliary system.
These tests measure how well the liver is performing its normal functions of clearing bilirubin, a blood waste product, and producing protein.
The liver cells release enzymes in response to disease or damage, which is what the other liver function tests measure. If the result of the test is abnormal, it does not necessarily mean you have a liver disease.
The main reasons for a liver function test are to:
Monitor the progression of diseases, such as alcoholic hepatitis or viral hepatitis, and at the same time determine how well a certain treatment is working
Screen for liver infections, such as hepatitis
Monitor possible side effects of medications
Measure the severity of a disease, especially cirrhosis or scarring of the liver
If one is experiencing symptoms of a liver disorder
If one is planning to become pregnant
The proteins and enzymes in the blood will also be checked in the liver function test. Levels that are above or below the norm may indicate liver problems.
There are many tests that can be performed on the liver, but its overall function is not measured by a majority of the tests. Some commonly used tests are ALT and AST tests. They measure the enzymes released by the liver in response to damage or disease. Albumin and bilirubin tests determine how well the albumin (a protein) is created by the liver and how well bilirubin (a waste product of the blood) is disposed of by the liver.
Aspartate transaminase (AST): This enzyme helps metabolize alanine, which is an amino acid that, in low levels of blood, is normally present like ALT. You may have liver disease or liver or muscle damage if there is an increase in AST levels.
Alanine transaminase (ALT): This enzyme helps your body metabolize protein. You may have liver damage if the levels increase once the ALT is released.
Aspartate transaminase is found in several parts of the body, including the heart, liver, and muscles. For liver damage, the levels of AST aren’t specific, hence, liver problems are usually diagnosed with ALT. ALT-to-AST ratio is used by the doctor for diagnosis. In cases of acute injury to the liver, the levels of ALT and AST may be used as general measures of the degree of liver inflammation or damage. But in cases of chronic diseases, they cannot be used since the enzymes may be within the normal range. AST and ALT are formerly referred to as SGPT and SGOT. Alanine transaminase and aspartate transaminase are normally found in liver cells, but when these cells are injured, they leak out of them. Since AST is also found in other organs, ALT is observed to be a more specific indicator of liver inflammation.
Albumin and total protein: This protein in the liver fights infections and performs other functions as well. You may have liver disease or damage if the total protein and albumin are lower than normal.
Alkaline phosphatase (ALP): This is an enzyme in the liver, bone, and bile ducts. You may have liver disease or damage, such as gall stone disease, alcohol abuse, drug-induced hepatitis, or in cases such as primary biliary cirrhosis or biliary tumors, blocked bile duct or certain bone diseases if the levels of ALP are higher than normal. Children and adolescents have high levels pf ALP due to increased bone turnover. Pregnancy also raises the level of ALP. This test is used to detect obstruction in the biliary system and is the most frequently used.
Albumin test: Albumin is an important main protein made by the liver that performs several bodily functions like nourishing the tissues, transporting hormones, vitamins and other substances throughout the body, and stopping leakage of fluid out of the blood vessels. This test measures how well the liver is making this protein. A low test result indicates the liver is not functioning properly.
Total protein: This measures both albumin and globulin in total, which are two main proteins. In liver disease, normally, as albumin levels rise, globulin levels fall. High values are seen In chronic active hepatitis and alcoholic hepatitis.
Gamma-glutamyltransferase (GGT): This is an enzyme in the blood that, if higher than normal, may indicate liver damage or bile duct damage. High levels are associated with bile duct damage and fibrosis. In more than 50% of patients with non-alcoholic fatty liver disease, GGT levels may be two to three times more than the upper reference value, and in about 30% of patients with chronic hepatitis C infection, GGT levels may be above the upper reference value.
Bilirubin: This is produced during the normal breakdown of red blood cells. It passes through the liver and then is excreted in the stool. Bilirubin gives bile its yellow-green color. Liver cells take in bilirubin and attach sugar molecules to it, which is then called “conjugated” bilirubin. This is then passed into the bile duct. There may be elevated levels of conjugated bilirubin in various liver and bile duct conditions, especially when the bile flow is blocked. When there is excessive breakdown of red blood cells, the level of unconjugated bilirubin rises. It occurs in hemolytic anemia and Gilbert’s syndrome. Healthy individuals have small amounts of bilirubin in their blood (<17μmol/L). You might have liver damage or liver disease or certain types of anemia if the levels of bilirubin are high (<50μmol/L); this is also known as jaundice. Destruction of red blood cells or a decrease in its removal from the bloodstream due to liver dysfunction may cause an increase in bilirubin levels.
Prothrombin time (PT): You may have liver damage if the PT is high and you are taking blood-thinning medicines such as warfarin. The liver has influence over blood-clotting factors; if the liver is damaged, the proper proteins will not be produced. PT and the INR tests help to assess blood clotting.
L-lactate dehydrogenase (LD): This is an enzyme found in the liver, and if its levels are high, you may have liver damage or certain disorders.
Other liver tests include:
Rise in the level of serum iron, ferritin, and transferrin saturation may indicate the presence of hemochromatosis. In Wilson’s disease, ceruloplasmin is reduced.
In children and adults, low levels of alpha-1-antitrypsin may indicate lung and/or liver disease.
Specific antibodies, proteins, and nucleic acids indicate the presence of hepatitis B or C.
Symptoms of nephritic syndrome (swelling around the eyes, belly, and legs)
Liver function tests guide the doctor along with medical history, physical examination, and diagnosis and management of liver diseases.
3 Potential Risks
Your doctor will obtain a blood sample by inserting a needle into a vein in the arm.
A liver function test may cause bruising or soreness at the injection site where the blood is drawn. Other risks include hematoma (bleeding under the skin), fainting, and infection.
4 Preparing for your Procedure
Complete instructions are given by the doctor about how to prepare for the blood sample part of the test. Your doctor will tell you to avoid eating and drinking or taking medications to prepare for a liver function test, because certain medications and foods can affect the results. You can also choose to wear a short-sleeve shirt or one in which the sleeves can be easily rolled up; this will make it easier for the doctor or nurse to draw blood.
First, the doctor or nurse will clean the skin with an antiseptic in order to prevent any micro-organisms from contaminating the test. An elastic band is then placed around the upper arm. Due to pressure, the veins swell with blood. The doctor or a nurse will get a sample of blood by inserting a needle into a vein in the arm; the needle is attached to a small tube to collect it. After this, the elastic band is removed.
As the needle is inserted into a vein in your arm, you may feel a quick pain and discomfort at the site. The doctor or nurse will place a bandage or gauze over the injected site to stop the bleeding. The procedure will only take a few minutes.
The blood sample is then sent to the laboratory for analysis, and the results will be available as early as that day if the analysis is done on site, or within several days if the lab analysis is done off site. Once the results are available, the doctor will review them. These results do not help the doctor determine the condition or degree of liver damage, but they can help decide further steps. The doctor will discuss the results during the follow-up appointment.
You can usually leave after the tests, however, if you feel faint or lightheaded during the blood draw, you should relax for a little while before you leave.
6 Procedure Results
Normal liver function test results include:
AST (8 to 48 units per liter or U/L)
ALT (7 to 55 U/L)
Albumin (3.5 to 5.0 grams per deciliter or g/dL)
ALP (45 to 115 U/L)
Bilirubin (0.1 to 1.2 milligrams per deciliter or mg/dL)
Total protein (6.3 to 7.9 g/dL)
LD (122 to 222 U/L)
GGT (9 to 48 U/L)
PT (9.5 to 13.8 seconds)
The results may be different for women and children; these are typical for adult men. The results may also vary from laboratory to laboratory.
With this test, your doctor can also check how your disease is progressing and if your body is responding to the treatment if you already have liver disease.
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