Liver Function Tests
There's no one test that indicates chronic hepatitis C disease. Tests for the effects of hepatitis C on your liver include:
Liver enzyme tests:
These tests measure current liver cell injury by the amount of enzymes that are "leaked" out of damaged or dying liver cells.
Liver function tests:
These tests look at levels of proteins made by the liver. If your liver damage is such that your liver function is impaired, levels of these proteins will be low. If your bilirubin, clotting factors, or albumin levels are low, you may have cirrhosis or late-stage liver disease.
Small amounts of ALT (alanine aminotransferase) are normally found in blood. When the liver is damaged, ALT is released into the bloodstream. ALT is found in organs other than the liver (kidneys, heart, muscles, and pancreas), but most increases in ALT are from liver damage.
The alanine aminotransferase test, also known as ALT, is one of a group of tests known as liver function tests (or LFTs) and is used to monitor damage to the liver.
ALT levels are used to detect liver abnormalities. Since the alanine aminotransferase enzyme is also found in muscle, tests indicating elevated AST levels might also indicate muscle damage. However, other tests, such as the levels of the MB fraction of creatine kinase should indicate whether the abnormal test levels are because of muscle or liver damage.
The alanine aminotransferase test (ALT) can reveal liver damage. It is probably the most specific test for liver damage. However, the severity of the liver damage is not necessarily shown by the ALT test, since the amount of dead liver tissue does not correspond to higher ALT levels. Also, patients with normal, or declining, ALT levels may experience serious liver damage without an increase in ALT.
Nevertheless, ALT is widely used, and useful, because ALT levels are elevated in most patients with liver disease. Although ALT levels do not necessarily indicate the severity of the damage to the liver, they may indicate how much of the liver has been damaged. ALT levels, when compared to the levels of a similar enzyme, aspartate aminotransferase (AST), may provide important clues to the nature of the liver disease. For example, within a certain range of values, a ratio of 2:1 or greater for AST: ALT might indicate that a patient suffers from alcoholic liver disease. Other diagnostic data may be gleaned from ALT tests to indicate abnormal results.
No special preparations are necessary for this test.
This test involves blood being drawn, probably from a vein in the patient's elbow. The patient should keep the wound from the needle puncture covered (with a bandage) until the bleeding stops. Patients should report any unusual symptoms to their physician.
Normal values vary from laboratory to laboratory, and should be available to your physician at the time of the test. An informal survey of some laboratories indicates many laboratories find values from approximately seven to 50 IU/L to be normal.
Low levels of ALT (generally below 300 IU/L) may indicate any kind of liver disease. Levels above 1,000 IU/L generally indicate extensive liver damage from toxins or drugs, viral hepatitis, or a lack of oxygen (usually resulting from very low blood pressure or a heart attack). A briefly elevated ALT above 1,000 IU/L that resolves in 24-48 hours may indicate a blockage of the bile duct. More moderate levels of ALT (300-1,000IU/L) may support a diagnosis of acute or chronic hepatitis.
It is important to note that persons with normal livers may have slightly elevated levels of ALT. This is a normal finding.
AST (aspartate aminotransferase) is also called SGOT (serum glutamic-oxaloacetic transaminase). Like ALT, AST is found mainly in the liver but also in other parts of the body. AST and ALT are usually measured together and are good indicators of liver disease or damage. Sometimes, test results give AST/ALT ratios.
The Aspartate aminotransferase test measures levels of AST, an enzyme released into the blood when certain organs or tissues, particularly the liver and heart, are injured. Aspartate aminotransferase (AST) is also known as serum glutamic oxaloacetic transaminase (SGOT).
The determination of AST levels aids primarily in the diagnosis of liver disease. In the past, the AST test was used to diagnose heart attack (myocardial infarction or MI) but more accurate blood tests have largely replaced it for cardiac purposes.
AST is determined by analysis of a blood sample, usually from taken from a venipuncture site at the bend of the elbow.
AST is found in the heart, liver, skeletal muscle, kidney, pancreas, spleen, lung, red blood cells, and brain tissue. When disease or injury affects these tissues, the cells are destroyed and AST is released into the bloodstream. The amount of AST is directly related to the number of cells affected by the disease or injury, but the level of elevation depends on the length of time that the blood is tested after the injury. Serum AST levels become elevated eight hours after cell injury, peak at 24-36 hours, and return to normal in three to seven days. If the cellular injury is chronic (ongoing), AST levels will remain elevated.
One of the most important uses for AST determination has formerly been in the diagnosis of a heart attack, or MI. AST can assist in determining the timing and extent of a recent MI, although it is less specific than creatine phosphokinase (CPK), CKMB, myglobin, troponins, and lactic dehydrogenase (LDH). Assuming no further cardiac injury occurs, the AST level rises within 6-10 hours after an acute attack, peaks at 12-48 hours, and returns to normal in three to four days. Myocardial injuries such as angina (chest pain) or pericarditis (inflammation of the pericardium, the membrane around the heart) do not increase AST levels.
AST is also a valuable aid in the diagnosis of liver disease. Although not specific for liver disease, it can be used in combination with other enzymes to monitor the course of various liver disorders. Chronic, silent hepatitis (hepatitis C) is sometimes the cause of elevated AST. In alcoholic hepatitis, caused by excessive alcohol ingestion, AST values are usually moderately elevated; in acute viral hepatitis, AST levels can rise to over 20 times normal. Acute extrahepatic (outside the liver) obstruction (e.g. gallstone), produces AST levels that can quickly rise to 10 times normal, and then rapidly fall. In cases of cirrhosis, the AST level is related to the amount of active inflammation of the liver. Determination of AST also assists in early recognition of toxic hepatitis that results from exposure to drugs toxic to the liver, like acetaminophen and cholesterol lowering medications.
Other disorders or diseases in which the AST determination can be valuable include acute pancreatitis, muscle disease, trauma, severe burn, and infectious mononucleosis.
The physician may require discontinuation of any drugs that might affect the test. These types include such drugs as antihypertensives (for treatment of high blood pressure), coumarin-type anticoagulants (blood-thinning drugs), digitalis, erythromycin (an antibiotic), oral contraceptives, and opiates, among others. The patient may also need to cut back on strenuous activities temporarily, because exercise can also elevate AST for a day or two.
Risks for this test are minimal, but may include slight bleeding from the blood-drawing site, fainting or feeling lightheaded after venipuncture, or hematoma (blood accumulating under the puncture site).
Normal ranges for the AST are laboratory-specific, but can range from 3-45 units/L (units per liter).
Striking elevations of AST (400-4000 units/L) are found in almost all forms of acute hepatic necrosis, such as viral hepatitis and carbon tetrachloride poisoning. In alcoholics, even moderate doses of the analgesic acetaminophen have caused extreme elevations (1,960-29,700 units/L). Moderate rises of AST are seen in jaundice, cirrhosis, and metastatic carcinoma. Approximately 80% of patients with infectious mononucleosis show elevations in the range of 100-600 units/L.
ALP (alkaline phosphatase) is found in all parts of the body, with particularly high concentrations in the liver, bone, and placenta (during pregnancy). Like ALT and AST, ALP might leak into the bloodstream when liver cells are damaged as a result of hepatitis C. Children (who have growing bones), pregnant women (especially in their last trimester), and people with bone disease also have higher levels of ALP.
GGT refers to gamma-glutamyl transferase, but it's also called gamma-glutamyl transpeptidase (GGTP) or Gamma-GT. High levels of GGT are found in the liver, bile ducts, and the kidney. Bloodstream GGT levels will be higher in people with diseases of the liver and bile ducts.
Higher levels of the enzyme 5'N'Tase (5'nucleotidase), also known as 5'NT, in your blood indicate a problem with bile secretion. Hepatitis or cirrhosis can cause a blockage of bile flow.
Albumin is the major blood protein made by the liver. One function of albumin is to keep the blood from leaking through the blood vessels, which can cause fluid retention in the ankles (edema), lungs, or abdomen (ascites).Low levels of albumin may be due to liver or kidney disease, malnutrition, or even a low-protein diet.
This pigmented (yellow) waste chemical comes from the normal process of red blood cells' dying after 90 to 120 days. A healthy liver converts bilirubin and sends it out of the body with the bile that goes to the intestine. Excreted bilirubin gives feces (stools) their characteristic brownish color.
When the liver is diseased, bilirubin isn't converted and excreted. Stools might, therefore, be light-colored. The bilirubin that's not properly excreted builds up in the body and gives a yellowish color to skin and eyes (a condition known as jaundice) and dark brown tea color to urine.
High levels of bilirubin are due to either too much production of bilirubin (from red blood cells dying) or because the liver isn't processing bilirubin, which happens when the liver is damaged. This is one of three tests used to determine wait time for a liver transplant.
In addition to using a blood test, urine can be tested for bilirubin.
The PT (prothrombin time) test measures how quickly your blood clots, which is dependent on clotting factors (proteins) that are made by the liver. The PT test is used as a marker of advanced liver disease and can indicate blood-clotting problems where it takes you longer to stop bleeding.
Your laboratory may also give PT results that have been converted to an internationally recognized and easily comparable value that's called the International Normalized Ratio (INR). The INR is one of the three factors used to determine wait time for a liver transplant.
Other blood tests
Additional tests that measure other markers in your blood give your doctor a clearer picture of any liver disease and also any effects from the combination peginterferon drug treatment.
Complete blood count (CBC)
A complete blood count (CBC) looks at the number and types of cells in your blood. Your doctor will look for problems such as
- Reduced white blood cells or platelets: This may indicate portal hypertension, a complication of cirrhosis in which pressures are increased in the portal vein.
- Indicators of anemia: This problem is very common during ribivarin treatment.
The complete blood count includes the following tests:
White blood cell (WBC) count:
The total number of white blood cells. Changes can indicate problems of hepatitis C infection or side effects of interferon treatment. Interferon can cause neutropenia, which is a decrease in neutrophils, one type of white blood cell.
- Red blood cell (RBC) count: The total number of red blood cells. Low levels can indicate anemia.
- Hematocrit (HCT): Percentage of blood cells that are red blood cells. Low levels can indicate anemia.
- Hemoglobin: The amount of this oxygen-carrying protein. Low levels can indicate anemia.
- Platelet count: Number of platelets in your blood (may be altered in cirrhosis).
Tests for AFP (alpha-fetoprotein) are used to screen for liver cancer in people with cirrhosis. But not everyone with liver cancer has this marker. Pregnant women usually have higher levels of this protein, which is also used to look for problems in pregnancy. You may have slightly high levels of this protein if you have hepatitis or cirrhosis.
The liver stores iron, and an overabundance of iron (iron overload) can add to the damage caused by hepatitis C. Too much iron can be a problem during interferon treatment. See your physician to determine whether you should avoid supplements that include iron.
Creatinine is actually a breakdown product of creatine, which is made by the liver and transported to your muscles. The kidneys excrete the waste product creatinine, and when your kidneys are damaged, creatinine levels rise. When the liver stops functioning in end-stage liver disease, this can cause serious kidney problems as well. This test is one of the three used to determine your wait time for a liver transplant.
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