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Jaundice in a newborn infant, however, is usually nonpathologic and results when the neonate’s still-developing liver is not yet able to eliminate bilirubin from the blood.
Hepatic vs. skeletal
Alkaline phosphatase (AP) is an enzyme found in high concentrations in bone, liver, bile ducts, the intestines, and placenta. It is released into the blood from diseased or damaged tissue and used to evaluate pathology of the bone and liver. The source of an elevated AP may be determined by examining the five varieties of AP, or isoenzymes, isolated from bone, liver, placental, biliary, and intestinal cells. However, due to the cost and complexity of such testing, the isoenzymes are infrequently examined. A more cost-effective test is the gamma-glutamyl transferase (GGT).
Gamma-glutamyl transferase (GGT), also known as gamma-glutamyl transpeptidase (GGT), is an excretory enzyme located in high concentrations in the liver, bile ducts, and kidneys. Because GGT is not found in bone tissue, an elevated GGT would indicate the liver as the source of an elevated AP. Increasing or decreasing GGT levels can be used in evaluating progression or regression of liver cancer. GGT is also useful in evaluating alcohol-induced liver disease and progress during alcohol detoxification.
Other screenings and monitors
of progress
Albumin is a protein produced by the liver. Its primary functions are to maintain oncotic pressure and transport small molecules, such as bilirubin, drugs, and hormones, in the blood. Because of a long half-life of 22 days, albumin levels are not useful in monitoring mild or acute liver disease. However, decreased albumin occurs with ascites, alcoholism, viral hepatitis, liver disease, malabsorption, malnutrition, and severe burns.
Prothrombin, a protein produced by the liver, is necessary for the clotting of blood. Serum prothrombin time (PT) is a measure of the clotting time of plasma. PT is useful for monitoring anticoagulation therapy and screening for homeostatic dysfunction as a result of liver disease, vitamin K deficiency, clotting factor deficiency (X, VII, V, II, I) or disseminated intravascular coagulation (DIC).
Ammonia (NH 3) is a natural byproduct of bacterial action on proteins in the intestines. NH 3 is transported to the liver via portal venous blood, where it is metabolized to urea and, finally, excreted by the kidneys. Blood ammonia levels are most useful in evaluating patients with stupor or coma of unknown origin, diagnosing Reye’s syndrome, evaluating patients receiving hyperalimentation therapy, and determining the progress of severe liver disease and response to therapy.
Lactic dehydrogenase (LDH) is an enzyme found in most tissues of the body but is particularly concentrated in the heart, liver, kidneys, and skeletal muscle cells. An elevated LDH level reflects tissue injury; however, to pinpoint the specific source of damage, the five LDH isoenzymes must be further analyzed. LDH levels rise in patients with burns, cancer, heart failure, stroke, and hepatitis. (See “Liver Function Tests” sidebar.)
Although LFTs make up only a portion of a complete clinical picture, understanding their complexities helps nurses fit a big piece into the diagnostic puzzle.
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Carolyn Penharlow, RN, MSN, ARNP, BC, is a nurse practitioner in employee health at Georgetown University Hospital, Washington, D.C., and Catherine Spader, RN, works in an ED in Bailey, Colo.
References
1. Bakerman S. Bakerman’s ABC’s of Interpretive Laboratory Data. 4th edition. Myrtle Beach, SC: Interpretive Laboratory Data, Inc.; 2002.
2. Chernecky CC, Berger BJ. Laboratory Tests and Diagnostic Procedures. 3rd ed. Philadelphia: WB Saunders; 2003.
Bibliography
Alsace NH, Maradiegue AH. Gastrointestinal health. In: Adult Primary Care. Meredith PV, Horan NM, eds. Philadelphia: WB Saunders; 2000: 380 – 430.
Fishbach FT. Overview of chemistry studies. Laboratory and diagnostic tests, 7th ed; 2004. Available at www3.georgetown.edu/dml/services/ ezproxy.html. Accessed
January 21, 2005.
Liver Function Tests. Compiled by the National Library of Medicine and National Institutes of Health. Available at www.nlm.nih.gov/medlineplus. Accessed January 21, 2005.
Seidel H, Ball JW, Dains JE, Benedict GW, eds. Mosby’s Guide to Physical Examination. 5th ed. St. Louis, Mo: Mosby Year Book; 2003.
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