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Lab Manual for UCSF Clinical Laboratories

Lab Manual for SFGH

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Item Value
Available Stat? Yes
Test code NH3
Performed by? Chemistry
Sendout? no
Price range $$
In House Availability 24 hours/7 days
Principle Ammonia reacts with a-ketoglutarate and NADPH to form L-glutamate and NADP in a reaction catalyzed by glutamate dehydrogenase. The change in absorbance (NADPH -> NADP) is proportional to the ammonia concentration.
Interpretation Ammonia is produced by endogenous protein catabolism and by bacteria in the GI tract. The liver converts ammonia to urea, which is excreted by the kidneys. Ammonia is elevated in:

1. fulminant hepatic failure and Reye's Syndrome;

2. inborn errors of metabolism;

3. increased ammonia may be an important factor contributing to pathogenesis of hepatic encephalopathy; correlation between plasma ammonia and clinical degree of encephalopathy is not close.

4. Valproate anticonvulsant therapy.
Container type gel or non-gel green top (lithium heparin or sodium heparin) tube
Amount to Collect 1 mL
Collection Instructions Caution: Avoid anticoagulants containing ammonium ion, i.e., ammonium heparin. Specimen must be sent to the laboratory in cup of ice within 30 minutes of collection.
Sample type Heparinized blood
Special instructions Hemolyzed specimens will not be assayed
Normal range 10 - 47 mcmol/L
Stability Specimens must be stored on ice and separated from cells within 30 minutes. Plasma is stable for 2 hrs at 4°C if tightly sealed.
Interferences False Increases: with hemolysis or with specimen storage at room temperature;

False Decreases: Glucose at or above 600 mg/dL can cause a decrease of 8 – 40 mcmol/L in ammonia concentrations.
Additional information On arrival in the laboratory, the cells will be separated immediately.
References 1. DCL Ammonia Assay 20002-10. October 1990. Diagnostic Chemicals Ltd. Oxford, CT.

2. Dufour, D.R.: Evaluation of Liver Function and Injury, in Clinical Diagnosis and Management by Laboratory Methods, 20th ed., p 264-280. W. B. Saunders. 2001.

3. Heubi, J.E. et al.: Grade I Reye's Syndrome-Outcome and Predictors of Progression Deeper Coma Grade, N Eng J Med, 311:1539, 198
CPT coding 82140
Last Updated 10/17/2012 10:11:07 AM
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