Analysis of a blood sample can provide essential information about the health of the liver and bile ducts (hepatobiliary system). The following are some of the basic blood tests used to evaluate the liver:
Enzyme tests. The liver is the site of many biochemical reactions that are controlled by numerous enzymes, including alanine aminotransferase (ALT), aspartate aminotransferase (AST), alkaline phosphatase (ALP), and gamma glutamyl transferase (GGT). Elevated levels of liver enzymes in the bloodstream may indicate liver damage; however, they do not necessarily point to a specific liver disease. Although enzyme tests may be ordered individually, they provide more information when performed in combination, since levels of many liver enzymes may be elevated in diseases affecting other organs.
Bilirubin, the main pigment in bile, is a breakdown product of hemoglobin, an iron-containing substance in red blood cells. Normally, only a small amount of bilirubin circulates in the blood. Elevated blood levels may result from many forms of liver and biliary tract disease, including hepatitis and bile duct obstruction. The presence of excess bilirubin in the blood produces a yellowish discoloration of the skin and eyes called jaundice.
Albumin is a major protein that, like most proteins in the bloodstream, is synthesized by the liver. A decreased level of albumin in the serum (the liquid portion of blood that remains after whole blood clots) is an indication of chronic liver disease.
Prothrombin time (PT) is a blood clotting study that may be performed to evaluate the function of the liver. Because prothrombin is one of the clotting proteins that is synthesized by the liver, an abnormal PT may reflect liver dysfunction.
Viral hepatitis tests may be done in people with abnormal liver enzymes whose medical history and/or symptoms raise suspicion of the disease. (Symptoms include low-grade fever, malaise, loss of appetite, and fatigue, but are not always present.) The three most common types of this virus found in the U.S. are hepatitis A, B, and C (known as HAV, HBV, and HCV); they are all detected by testing for the presence of specific antigens or antibodies found only in the blood of infected individuals. Different antibody/ antigen tests may be performed, depending on which hepatitis type is suspected. In addition, the presence of particular antibodies can signal whether the infection is in an acute or chronic stage.
Purpose of Blood Tests to Evaluate the Liver
- Liver enzymes, albumin, and prothrombin time are tested to evaluate liver function, to help diagnose diseases of the liver and bile ducts, and to monitor the progress of known liver disease.
- Viral hepatitis antibodies are used to diagnose viral hepatitis infection, determine the type of the disease (A, B, C, or another variant), and establish the current status of the disease (acute or chronic).
- All blood donors are automatically screened for the presence of hepatitis B and C.
- Monitor medications that can damage the liver.
Who Performs Blood Tests to Evaluate the Liver
- A doctor, a nurse, or a technician draws the blood sample.
Special Concerns about Blood Tests to Evaluate the Liver
- A number of medications and vitamin supplements can alter the levels of bilirubin and liver enzymes and interfere with test results.
- Liver enzyme levels may be affected by a variety of factors other than liver disease, including pregnancy, periods of rapid bone growth, alcohol consumption, obesity, strenuous exercise, consumption of particular foods, trauma, and surgery.
- Even a moderate alcohol intake can raise levels of the GGT enzyme.
- People who have been inoculated with the hepatitis B vaccine may have antibodies in their blood even though they are not infected; this may lead to a false-positive result.
Before Blood Tests to Evaluate the Liver
- Report to your doctor any medications, herbs, or supplements you are taking. You may be advised to discontinue certain of these agents before a liver enzyme test.
- You are usually asked to avoid eating or drinking for at least 8 hours prior to a liver enzyme test, but fasting requirements vary for different laboratories.
What You Experience
- A sample of your blood is drawn from a vein, usually in your arm, and sent to a laboratory for analysis.
Risks and Complications of Blood Tests to Evaluate the Liver
- Possible complications include fainting or feeling lightheaded, a lump or bruise under the skin (hematoma) and pain associated with locating a vein.
After Blood Tests to Evaluate the Liver
- Immediately after blood is drawn, pressure is applied (with cotton or gauze) to the puncture site.
- Resume your normal diet and any medications withheld before the test, according to your doctor’s instructions.
- Blood may collect and clot under the skin (hematoma) at the puncture site; this is harmless and will resolve on its own. For a large hematoma that causes swelling and discomfort, apply ice initially; after 24 hours, use warm, moist compresses to help dissolve the clotted blood.
Results of Blood Tests to Evaluate the Liver
- Your blood sample is sent to a laboratory for analysis. A physician will review the results for any evidence of liver injury or disease.
- These tests are frequently the first step in assessing potential liver disorders. Abnormal results often necessitate additional tests to evaluate the structure and function of the liver—such as a CT scan, ultrasound, MRI, or liver biopsy—in order to establish a diagnosis.
- If antigen/antibody tests indicate the presence of acute or chronic viral hepatitis, a liver biopsy may be required to confirm the diagnosis and assess the degree of damage to the liver.
The Johns Hopkins Consumer Guide to Medical Tests
Simeon Margolis, M.D., Ph.D., Medical Editor
Updated by Remedy Health Media