amylase in 24 hour urine
Reference interval
- 48-444 U/24 Hours
Principle
Amylase is a relatively small protein (MW 45,000 daltons) & is therefore filtered readily in the urine. The enzyme can be found in increased concentrations in the urine for longer periods of time than in the serum.
In the ACA amylase method, amylase catalyzes the hydrolysis of a defined substrate, maltopentaose (a linear polymer of 5 glucose units in a-1,4 linkage), to yield maltotriose & maltose. The hydrolysis of these products by a-glucosidase yields a total of 5 moles of glucose for each mole of maltopentaose hydrolyzed. Hexokinase catalyzes the phosphorylation of glucose by adenosine-5'-triphosphate (ATP) to glucose-6-phosphate (G-6-P) which, in turn, is oxidized by nicotinamide adenine dinucleotide (NAD) in the presence of glucose-6-phosphate dehydrogenase (G6PD). The change in absorbance at 340 nm due to the formation of reduced NAD (NADH) over a 17.07 second measurement period is proportional to the amylase activity, since other reactants are present in non-rate-limiting quantities. Because the measured species, NADH, is stoichiometrically related to the substrate, amylase measurements can be expressed directly in U/L. Endogenous glucose, which might interfere with amylase determinations, is removed from the sample during passage through a gel filtration column in the pack header.
Clinical significance
Assays of amylase activity in serum & urine are largely of use in the diagnosis of disease of the pancreas & in the investigation of pancreatic function. In acute pancreatitis associated with hyperlipidemia, serum amylase activity may be normal. A significant amount of the serum amylase is excreted in the urine, & therefore elevation of serum activity is reflected in the rise of urinary amylase activity. Urine amylase, as compared with serum amylase, appears to be more frequently elevated, reaches higher levels, & persists for longer periods. The urinary clearance of amylase is markedly increased in acute pancreatitis. In quiescent chronic pancreatitis, both serum & urine activities are usually within the reference ranges.
Increases
Decreases
Specimen
10 mL aliquot of a 24 hour urine collection. Proper 24 hour urine collection procedure should be followed, & collection should be refrigerated at 2-6 degrees C prior to analysis.
Albumin is added to maximize activity (>0.25g albumin/L)
More general terms
Additional terms
References
- ↑ Tietz, Norbert W., Textbook of Clinical Chemistry, W.B. Saunders Company, Philadelphia, PA, 1986, pp. 725-734.
- ↑ Kaplan, Lawrence A. & Pesce, Amadeo J., Clinical Chemistry: Theory, Analysis, & Correlation, 2nd Edition, The C.V. Mosby Company, St. Louis, MO, 1989, pp.395-396.
- ↑ Henry, John Bernard, M.D., Clinical Diagnosis & Management by Laboratory Methods, 18th Edition, W.B. Saunders Company, Philadelphia, PA, 1991, pp. 529-31.
- ↑ ACA IV Discrete Clinical Chemistry Analyzer Instrument Manual, Volume 3A, Chapter 6: Test Methodology, AML 20.
- ↑ Clinical Guide to Laboratory Tests, 4th edition, HB Wu ed, WB Saunders, Philadelphia, 2006
- ↑ Panel of 7 tests Laboratory Test Directory ARUP: http://www.aruplab.com/guides/ug/tests/0020471.jsp