Ammonia tolerance test

The ammonia tolerance test (C. van Caulaert et al., 1932 E. Kirk, 1936) is carried out with the oral administration of 4—5 g ammonium acetate or 3 g ammonium chloride. Normally, there is no significant elevation of ammonia levels after 30, 60 and 120 minutes. In hepatic cirrhosis and in portacaval anastomosis, there is a clear elevation with delayed normalization. (49)... 

Castell, D.O. The ammonia tolerance test an index of portal hypertension. Gastroenterology 1965 49 539-543... 

The system can tolerate a high amount of water in the eluate and also organic acids or ammonia for pH adjustment. Buffered solvent systems will increase the noise level and can be used only in low amounts. Gradient elution is important for complex samples and will be tested in the near future. 

At this point, we would like to emphasize once again that a strict lactovegetarian protein supply must be adhered to not only in latent encephalopathy, but also in (acute or chronic) liver diseases in which insufficient detoxification of ammonia is anticipated. When assessing the so-called protein tolerance threshold (s. p. 278), the documentation sheet (s. fig. 15.3) as well as a psycho-motoric test programme (s. p. 203) can be of great help. 

Azaguanine inhibited the development of tolerance in mice to the analgesic effect of morphine. Kits for the clinical measurement of guanase, the most sensitive of all tests for liver damage, consisted of 8-azaguanine in bis(hydroxyethyl)glycine buffer. The evolved ammonia was measured col-orimetrically. ... 

Nicely, P.A., Phillips, B.M., Anderson, B.S., Hunt, J.W., Huntley, S.A., Tjeerdema, R.S., Palmer, F.H. and Carley, S. (2000) Tolerance of Several Marine Toxicity Test Organisms to Ammonia and Artificial Salts (Abstract Book). Society of Toxicology and Chemistry, Nashville, TN. 

The test tube is moved to a 20°C water bath and stirred for 5 min, and this procedure must not dissolve the precipitate. Many of the other alkali metals, in addition to ammonia, will also precipitate as a methoxyphenylacetic acid salt if present in a high concentration. But contrary to the sodium salt they will redissolve when transferred to this higher temperature. It should be noted, however, that "high concentrations" in this context equal as much as 8 M in the case of magnesium and 2.3 M in the case of potassium. Cesium will interfere in the test if present in the test solution in a concentration of 10 mg/ml. Lithium is tolerated in 30 mg/ml. 

Ammonia metabolism within the muscle may be improved by the administration of L-omithine-L- aspartate (LOLA). Controlled trials suggest that enteral and parenteral formulations of ornithine aspartate significantly reduce blood ammonia levels and have useful therapeutic effects in patients with cirrhosis and encephalopathy (Kircheis et al., 1997 Stauch et al., 1998). Poo et al. (2006) recently showed in a randomized, lactulose-controlled study of oral ornithine-aspartate in 20 patients with clinically overt HE that LOLA in contrast to lactulose significantly improved parameters of mental status, number connection test scores, asterixis scores and EEG. Both lactulose and LOLA reduced serum ammonia levels and improved quaUty of life scores. Since only 20 patients were included in this study the results cannot be considered proof for the superiority of LOLA compared to lactulose, while the data underscore the effect of both agents. Ornithine aspartate is well tolerated in general. From a theoretical point of view the combination of disaccharides and ornithine aspartate may be useful in patients with insufficient efficacy of only one of the two drugs. 

Protein load A protein load is done when a diagnosis is unclear or for heterozygote detection in OTC deficiencies. After one has determined a daily profile for pre- and postprandial ammonia and the amino acids in a self chosen diet, the protein content should be estimated per meal. The patient should not be in a catabolic but steady state for at least 4 days. For women, the test should be avoided around the period of menstruation. The protein load is, in contrast to the allopurinol test, also useful for assessing protein tolerance. False negatives have been described in conjunction with OTC heterozygote testing skewed toward a predominance of wild-type OTC. 

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