Ammonia in blood

Table 10.1 Concentration of ammonia in blood and other tissues of the rat...

The toxicity of ammonia was dramatically demonstrated by experiments carried out as early as 1931 injection of the enzyme urease, which catalyses the conversion of urea to ammonia, into rabbits rapidly caused their death. The normal concentration of ammonia in blood is about 0.02 mmol/L toxicity becomes apparent at a concentration of abont 0.2 mmol/L or above (see Table 10.1). Ammonia toxicity in very young children is usually associated with vomiting and eventually coma. It is almost invariably due to the deficiency of an enzyme of the urea cycle (see below). In adults, ammonia accnmulation, and hence toxicity, usually results from damage to the liver caused by poisons, alcohol or viral infection. 

Fig. 50.—In vivo experiments with rumen-fistulated lambs with urea and starch-urea complex, measured as the concentration of ammonia in blood. (Reprinted with permission from J. Hollo, L. Fodor, and S. Gal, Staerke, 31 (1979) 303-306.)...

The determination of ammonia in blood is carried out enzymatically, which is considered to be specific, precise and simple. (48) Serious mistakes can easily occur during the preanalytical phase of ammonia determination, making it imperative to comply with the standardized method of taking a blood sample, (s. p. 91) EDTA blood should be taken with the addition of sodium borate and L-serine. Furthermore, elevated serum y-GT activity and increased thrombocytes cause the ammonia level to rise, as does cigarette smoking prior to blood collection. Even minor haemolysis (e. g. in the event of prolonged transport) will spoil the blood for ammonia determination, since the ammonia concentration of erythrocytes is three times that found in plasma. Besides these interfering factors, ammonia concentration is influenced by (7.) the metabolic performance of the urea cycle, (2.) the extrahepatic formation and elimination of ammonia, and (5.) the acid-base status. 

M7. Meyerhoff, M. E., and Robins, R. H., Disposable potentiometric ammonia gas sensors for estimation of ammonia in blood. Anal. Chem. 52, 2383-2387 (1980). 

T. Aoki, S. Uemura, and M. Munemori, Flow Injection Analysis with Membrane Separation. Determination of Ammonia in Blood and Urine [in Japanese]. Bunseki Kagaku, 33 (1984) 505. 

The activity of mitochondrial carbamoyl phosphate synthetase (CPS) depends on the availability of N-acetylglutamate, which is generated from glutamate and acetyl CoA. A reduction in the availability of the activating molecule will lead to a decrease in the activity of CPS, which utilizes ammonia and bicarbonate for the synthesis of carbamoyl phosphate. This, in turn, leads to an increase in the level of ammonia in blood and urine. Over two-thirds of patients with methylmalonic aciduria are hyperammonemic. 

There are tests that can detect ammonia in blood and urine. However, these tests cannot definitely determine if you have been exposed because ammonia is normally found in the body. 

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