ammonia (NH3) in plasma
Indications
- evaluation of hyperammonemia due to
Reference interval
Principle
The Kodak Ektachem clinical Chemistry Slide (NH3/AMON) quantitatively measures ammonia concentration in plasma.
The Kodak Ektachem Clinical Chemistry Slide (NH3/AMON) contains a dry, multilayered analytical element coated on a clear polyester support. It is a COLORIMETRIC test.
A 10 uL drop of sample is deposited on the slide & is evenly distributed by the spreading layer. Water & nonproteinaceous components travel to the underlying buffered reagent layer, & the ammonium ions are converted to gaseous ammonia.
The semipermeable membrane allows only ammonia to pass through & prevents buffer or hydroxyl ions from reaching the indicator layer.
After a fixed incubation period, the reflection density of the dye is measured spectrophotometrically through the transparent support, using the white background of the spreading layer as a diffuse reflector.
The following reaction sequence takes place:
NH3 + Bromphenol Blue ------------> Blue Dye
Clinical significance
- ammonia is a waste product of protein catabolism; it is potentially toxic to the central nervous system
- an increased plasma ammonia may be indicative of hepatic encephalopathy, hepatic coma in terminal stages of liver cirrhosis, hepatic failure, acute & subacute liver necrosis, or Reye's syndrome.
- hyperammonemia may also be found with increasing dietary protein intake.
- the major source of circulating ammonia is the gastrointestinal tract, where ammonia is derived from the action of bacterial proteases, ureases, & amine oxidases on the contents of the colon as well as from the hydrolysis of glutamine in both the small intestine & colon
- under normal circumstances most of the portal vein ammonia load is metabolized to urea in hepatocytes in the Krebs-Henseleit urea cycle during the first pass through the liver.
- plasma NH3 levels are useful in monitoring patients on hyperalimentation therapy.
Increases
- clinical disorders
- pharmaceutical agents:
- chemical interferences
Specimen
No special patient preparation is required.
A green top tube containing 5 mL of Na heparin should be used for specimen collection.
For plasma preparation: Collect the specimen by standard venipuncture technique & keep on ice. Ammonia levels can increase in vitro due to the breakdown of nitrogen-containing blood components; therefore, remove plasma promptly from the cells. If not analyzed immediately, refrigerate the specimen at 2-8 C. Freeze specimens for long-term storage or shipment.
Serum should NOT be used for ammonia measurements, because ammonia is produced during the clotting process.
Minimum sample size 0.5 milliliter: with as optimum size of 1.0 milliliter or larger.
More general terms
Additional terms
Component of
References
- ↑ Tietz, N., Fundamental of Clinical Chemistry, 3rd Edition, W. B. Saunders Company, Philadelphia, 1987, p.748.
- ↑ Kodak Ektachem 700 Analyzer Operator's Manual, Kodak Clinical Product, Eastman Kodak Company, Rochester, New York.
- ↑ Package Insert, Kodak Ektachem Clinical Chemistry Slide (NH3/AMON), Kodak Clinical Products Division, Eastman Kodak Company, Rochester, New York.
- ↑ Clinical Guide to Laboratory Tests, 3rd ed. Teitz ed., W.B. Saunders, 1995.
- ↑ Clinical Diagnosis & Management by Laboratory Methods, 19th edition, J.B. Henry (ed), W.B. Saunders Co., Philadelphia, PA. 1996, pg 10.
- ↑ Ammonia, Plasma Laboratory Test Directory ARUP: http://www.aruplab.com/guides/ug/tests/0020043.jsp