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ammonia (NH3) in plasma

Indications: - evaluation of hyperammonemia due to a) fulminant hepatic failure b) Reye's syndrome c) cirrhosis d) gastrointestinal bleeding e) porto-systemic shunting of blood f) renal disease g) obstructive uropathy - genitourinary tract infection - *distension & urinary stasis h) inborn metabolic disorders of the urea cycle Reference values: - Male & Female: 20-120 ug/dL; 12-70 umol/L 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: 1) clinical disorders a) fulminant hepatic failure b) Reye's syndrome c) cirrhosis d) gastrointestinal bleeding e) porto-systemic shunting of blood f) renal disease g) genitourinary tract infection with distension & stasis h) inborn metabolic disorders of the urea cycle (see hyperammonemia) 2) pharmaceutical agents: -> chemical interferences -> isoniazid 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 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.

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NH3; ammonia

General

ammonia (NH3) in body fluid

References

  1. Tietz, N., Fundamental of Clinical Chemistry, 3rd Edition, W. B. Saunders Company, Philadelphia, 1987, p.748.
  2. Kodak Ektachem 700 Analyzer Operator's Manual, Kodak Clinical Product, Eastman Kodak Company, Rochester, New York.
  3. Package Insert, Kodak Ektachem Clinical Chemistry Slide (NH3/AMON), Kodak Clinical Products Division, Eastman Kodak Company, Rochester, New York.
  4. Clinical Guide to Laboratory Tests, 3rd ed. Teitz ed., W.B. Saunders, 1995.
  5. Clinical Diagnosis & Management by Laboratory Methods, 19th edition, J.B. Henry (ed), W.B. Saunders Co., Philadelphia, PA. 1996, pg 10.
  6. Ammonia, Plasma Laboratory Test Directory ARUP: 20043

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