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Liver Function Tests (LFT)
The liver is one of the most important organs in the body. As the body's "chemical factory," it regulates the levels of most of the main blood chemicals and acts with the kidneys to clear the blood of drugs and toxic substances. The liver metabolizes these products, alters their chemical structure, makes them water soluble, and excretes them in bile. Liver function tests are used to determine if the liver has been damaged or its function impaired.
Liver function tests, or LFTs, may include tests like Bilirubin, SGPT, SGOT, Albumin, Alkaline Phosphatase, Gamma Glutamyl Transferase.
Bilirubin (Total and Conj.)
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). Differentiating 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). Bilirubin measurements are especially valuable in newborns, as extremely elevated levels of unconjugated bilirubin can accumulate in the brain, causing irreparable damage.
Alanine aminotransferase (ALT), formerly called serum glutamate pyruvate transaminase, or SGPT, is an enzyme necessary 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 jaundice. Additionally, in conjunction with the aspartate aminotransferase test (AST), it helps to distinguish between heart damage and liver tissue damage.
Aspartate aminotransferase (AST), formerly 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.
Albumin is the most abundant protein in the blood plasma. It keeps fluid from leaking out of blood vessels and nourishes tissues. It helps in keeping water in blood vessels and transport substances like harmones, vitamins, drugs, ions like calcium throughout the body. Albumin is made in the liver and is extremely sensitive to liver damage. The concentration of albumin drops when the liver is damaged, or with kidney disease (nephrotic syndrome), or when a person is malnourished, or if a person experiences inflammation in the body, or with shock. Decreased albumin levels can be associated with malnutrition, liver disease, and kidney disease. Albumin level increases when a person is dehydrated.
Alkaline phosphatase (ALP) levels usually include two similar enzymes (isoenzymes) that mainly 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
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. It is also commonly elevated in patients with infectious mononucleosis.
The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition. A licensed physician should be consulted for diagnosis and treatment of any and all medical conditions.