WHAT ARE LIVER FUNCTION TESTS?
Liver function tests are blood tests used to help diagnose and monitor liver disease or damage. The tests measure the levels of certain enzymes and proteins in your blood.
Some of these tests measure how well the liver is performing its normal functions of producing protein and clearing bilirubin, a blood waste product. Other liver function tests measure enzymes that liver cells release in response to damage or disease.
Conditions other than liver disease or damage can lead to abnormal liver function test results. Test results can be normal in people who have liver disease or damage.
The tests included in the profile are as follows:
- Bilirubin (Total, Direct, Indirect)
- Protein (total, albumin, globulin, AG ratio)
- Alkaline phosphatase
WHY DO WE NEED TO DO LIVER FUNCTION TESTS?
Liver function tests can be used to:
- Screen for liver infections, such as hepatitis (jaundice),
- Monitor the progression of a disease and determine how well a treatment is working
- Measure the severity of a disease, particularly scarring of the liver (cirrhosis)
- Monitor possible side effects of medications
WHY DO WE NEED TO DO LIVER FUNCTION TESTS?
Liver tests may be done together in a panel or tested separately. Some common liver function tests include:
When liver cells are damaged or destroyed, the enzymes in the cells leak out into the blood, where they can be measured by blood tests. Liver tests check the blood for two main liver enzymes:
- Aspartate aminotransferase (AST), formerly called SGOT. The AST enzyme is also found in muscles and many other tissues besides the liver.
- Alanine aminotransferase (ALT), formerly called SGPT. ALT is almost exclusively found in the liver. If ALT and AST are found together in elevated amounts in the blood, liver damage is most likely present.
- Alkaline phosphatase (ALP). ALP is an enzyme in the liver, bile ducts and bone. Higher than normal levels of ALP may indicate liver damage or disease, such as a blocked bile duct, or certain bone diseases.
- Albumin and total protein. Albumin is one of several proteins made in the liver. Your body needs these proteins to fight infections and to perform other functions. Lower than normal levels of albumin and total protein may indicate liver damage or disease.
- Bilirubin. Bilirubin is a substance produced during the normal breakdown of red blood cells. Bilirubin passes through the liver and is excreted in stool. Elevated levels of bilirubin (jaundice) may indicate liver damage or disease.
- Gamma-glutamyltransferase (GGT). GGT is an enzyme in the blood. Higher than normal levels may indicate liver or bile duct damage.
- L-lactate dehydrogenase (LDH). LDH is an enzyme found in the liver. Elevated levels may indicate liver damage
- Prothrombin time (PT). PT is the time it takes your blood to clot. Increased PT may indicate liver damage.
- International normalized ratio (INR): Not really a test, but a standardized way for all labs to report PT, so their results can be compared accurately with each other.
- PT and INR rise in people with severe liver disease because the liver fails to make normal amounts of certain clotting factors. An elevated PT can have many other causes besides liver disease.
WHAT DO LIVER FUNCTION TESTS INCLUDE?
Normal blood test results for typical liver function tests include:
- ALT. 7 to 55 units per liter (U/L)
- AST. 8 to 48 U/L
- ALP. 45 to 115 U/L
- Albumin. 3.5 to 5.0 grams per deciliter (g/dL)
- Total protein. 6.3 to 7.9 g/dL
- Bilirubin. 0.1 to 1.0 mg/dL
- GGT. 9 to 48 U/L
- LDH. 122 to 222 U/L
- PT. 9.5 to 13.8 seconds
These results are typical for adult men. Normal results may vary slightly from laboratory to laboratory, and be slightly different for women and children. Results may also be affected by certain foods or medications. Be sure to mention any foods or medications you’ve eaten or taken so that your doctor can correctly interpret your results.
The farther from normal the test results are, the more likely you are to have significant liver disease. Your doctor will use these results to help determine any treatment that may be needed. If you already have liver disease, liver function tests can help determine how your disease is progressing and if you’re responding to treatment.