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Liver Function Tests
 

What Is A Liver Function Test?
Liver function tests,sometimes called LFT's, include tests for bilirubin and ammonia. LFTs often include tests to measure levels of several enzymes, which are special proteins that help the body break down and use other substances. Enzymes that are often measured in LFTs include GGT, ALT or SGPT, AST or SGOT, and ALP. LFTs may also include prothombin time (PT), a measure of how long it takes for the blood to clot.
 
What Does It Determine?
Liver function tests are used to determine if the liver has been damaged or its function impaired. Elevations of certain liver tests in relation to others aids in that determination. For example, aminotransferases are notably elevated in liver damage caused by liver cell disease (hepatocellular disease). However, in intrahepatic obstructive disease—which may be caused by some drugs or biliary cirrhosis—the alkaline phosphatases are most abnormal.
 
Alanine aminotransferase (ALT) ,previously called serum glutamate pyruvate transaminase, or SGPT, is an enzyme that is needed for energy production. It is present in a number of tissues, including the liver, heart, and skeletal muscles, but is found in the highest concentration in the liver. Because of this, it is used in conjunction with other liver enzymes to detect liver disease, especially hepatitis or cirrhosis without jauncide. Additionally, in conjunction with the AST, it helps to distinguish between heart damage and liver tissue damage.
 
Aspartate aminotransferase (AST), previously called serum glutamic-oxaloacetic transaminase, or SGOT, is another enzyme necessary for energy production. It, too, may be elevated in liver and heart disease. In liver disease, the AST increase is usually less than the ALT increase. However, in liver disease caused by alcohol use, the AST increase may be two or three times greater than the ALT increase.
 
Alkaline phosphatase (ALP) levels usually include two similar enzymes (isoenzymes) that primarily come from the liver and bone and from the placenta in pregnant women. In some cases, doctors may order a test to differentiate between the alkaline phosphatase that originates in the liver and the alkaline phosphatase originating in bone. If a person has elevated ALP, does not have bone disease and is not pregnant, he or she may have a problem with the biliary tract, the system that makes and stores bile. (Bile is made in the liver, then passes through ducts to the gall bladder, where it is stored.)
 
Gamma-glutamyl transferase (GGT), sometimes called gamma-glutamyl transpeptidase (GGPT), is an enzyme that is compared with ALP levels to distinguish between skeletal disease and liver disease. Because GGT is not increased in bone disorders, as is ALP, a normal GGT with an elevated ALP would indicate bone disease. Conversely, because the GGT is more specifically related to the liver, an elevated GGT with an elevated ALP would strengthen the diagnosis of liver or bile-duct disease. The GGT has also been used as an indicator of heavy and chronic alcohol use, but its value in these situations has been questioned recently.
 
Bilirubin, a breakdown product of hemoglobin, is the predominant pigment in a substance produced by the liver called bile. Excess bilirubin causes yellowing of body tissues (jaundice). There are two tests for bilirubin: direct-reacting (conjugated) and indirect-reacting (unconjugated). Distinguishing between the two is important diagnostically, as elevated levels of indirect bilirubin are usually caused by liver cell dysfunction (e.g. hepatitis), while elevations of direct bilirubin typically result from obstruction either within the liver (intrahepatic) or a source outside the liver (e.g. gallstones or a tumor blocking the bile ducts).
 
Ammonia Analysis of blood ammonia aids in the diagnosis of severe liver diseases and helps to monitor the course of these diseases. Ammonia levels are also helpful in the diagnosis and treatment of hepatic encephalopathy, a serious brain condition caused by the accumulated toxins that result from liver disease and liver failure.

WHAT DO THE RESULTS MEAN?
Reference ranges vary from laboratory to laboratory and also depend upon the method used. However, normal values are generally framed by the ranges shown below. Values for enzymes are based upon measurement at 37°C.ALT: 5–35 IU/L. (Values for the elderly may be slightly higher, and values also may be higher in men and in African-Americans.)

• ALP: 30–120 IU/LALP is higher in children, older adults and pregnant females.
• GGT: males 2–30 U/L; females 1–24 U/L.
• LDH: 0–4 days old: 290–775 U/L; 4–10 days: 545–2000 U/L; 10 days–24 months: 180–430 U/L; 24 months–12 years: 110–295 U/L; 12–60 years: 100–190 U/L; 60 years: >110–210 U/L.
• Bilirubin: (Adult, elderly, and child) Total bilirubin: 0.1–1.0 mg/dL; indirect bilirubin: 0.2–0.8 mg/dL; direct bilirubin: 0.0–0.3 mg/dL.
• Ammonia: 10–70 micrograms per dL (heparinized plasma). Normal values for this test vary widely, depending upon the age of the patient and the type of specimen.
• Alblumin:  3.2-5.4 g/L.

ABNORMAL RESULTS
 
ALT: Values are significantly increased in cases of hepatitis, and moderately increased in cirrhosis, liver tumors, obstructive jaundice, and severe burns. Values are mildly increased in pancreatitis, heart attack, infectious mononucleosis, and shock. Most useful when compared with ALP levels.
 
AST: High levels may indicate liver cell damage, hepatitis, heart attack, heart failure, or gall stones.
 
ALP: Elevated levels occur in diseases that impair bile formation (cholestasis). ALP may also be elevated in many other liver disorders, as well as some lung cancers and Hodgkin's lymphoma. However, elevated ALP levels may also occur in otherwise healthy people, especially among older people.
 
GGT: Increased levels are diagnostic of hepatitis, cirrhosis, liver tumor or metastasis as well as injury from drugs toxic to the liver. GGT levels may increase with alcohol ingestion, heart attack, pancreatitis, infectious mononucleosis, and Reye's syndrome.
 
LDH: Elevated LDH is seen with heart attack, kidney disease, hemolysis, viral hepatitis, infectious mononucleosis, Hodgkin's disease, abdominal and lung cancers, germ cell tumors, progressive muscular distrophy, and pulmonary embolism. LD is not normally elevated in cirrhosis.
 
Bilirubin: Increased indirect or total bilirubin levels can indicate various serious anemias.  Increased direct bilirubin levels can be diagnostic of bile duct obstruction, gallstones, cirrhosis, or hepatitis
 
Ammonia: Increased levels are seen in primary liver cell disease, Reye's syndrome, severe heart failure, hemolytic disease of the newborn, and hepatic encephalopathy..
 
Albumin: Albumin levels are increased due to dehydration. They are decreased due to a decrease in synthesis of the protein which is seen in severe liver failure and in conditions such as burns or renal disease that cause loss of albumin from the blood.
 
Be sure to speak with your treatment team about any abnormal results and get an informed explanation of how these values reflect the status of your own health. It is important to have guidance and direction from your medical care provider.