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KMID : 0378019630060110045
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New Medical Journal
1963 Volume.6 No. 11 p.45 ~ p.55
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pH and alkali, Decisive Factors in Determination of True Blood Ammonia
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Abstract
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An attempt was made to determine the origin of artifactual blood ammonia formed in the shed blood; "xperimentation, with blood specimens from more than 400 healthy individuals, was carried out over a period of four and a half years, utilizing two popular microdiffusion blood ammonia methods, those of Seligson and Conway.
The actions of several alkali (potassium carbonate, carbonatebicarbonate mixture and boratesodium hydroxide (with a pH of 9 to 11.4)) were compared by placing them in (the diffusion apparatus with specimens of blood. It was found that the ammonia concentration;´tended to be higher with increasing pH and vice versa lowering with decreasing pH. While occasional extremely implausible results were obtained in experiments using the potassium carbonate and carbonate-bicarbonate mixture, on the other hand, no such aberrations were observed with borate-sodium hydroxide. Within the pH range, from 9 to 10. 1, the yield of ammonia when plotted against the pH of the blood-alkali mixture showed a straight line. Increasing beyond 10, resulted in an asymptomatic character of diffusion curve. For these reasons, borate-sodium hydroxide reagent which results in a pH of 10. 1 in the presence of blood, is selected as the choice of weak alkali media for the determination of true blood ammonia.
The author has to abandon his earlier thought that aberrations in ammonia analyses can be largely attributed to faulty technique in collecting and handling blood. Careful control of these techniques resulted in some lowering of the ammonia concentration, but failed to prevent the more serious aberrations encountered.
In search for clarification of the origin of extra ammonia, studies were carried out by experimenting with glutamine, both in aqueous solutions and following mixture with blood. The results suggest that non-protein glutamine is an unlikely source of extra ammonia.
The only other plausible source of the extra ammonia liberated from blood, therefore, seemed to be the blood proteins. Accordingly, the action of various alkaline reagents on plasma albumin, globulin and on whole blood was tested, after prolonged dialysis to remove preformed ammonia. Ammonia was released from each of the protein solutions used. However, the action of borate in this release was less pronounced than that of the carbonate-bicarbonate mixture. This latter mixture, in turn, liberated substantially less ammonia than did potassium carbonate. Therefore, it is concluded that the origin of artifactual ammonia may be traced to the decomposition of protein by the action of alkali.
The author has revised the method of measuring blood ammonia in such a way as to avoid spontaneous production of ammonia from blood proteins. The technique involves the use of sodium borate buffer at a pH of 10.80.2, which, when mixed with blood, results in a pH of 10.1. The adequacy of this technic is well proven by the satisfactory results obtained in a large number of recovery studies.
The technique described, applied to venous specimens that were collected in EDTA tubes and promptly analyzed, was used to study a group of 16 healthy persons, 20 to 25, male, with no history of previous liver involvement. The mean blood ammonia was 0.42 ug./ml. expressed as N. The lowest value was 0.21, the highest, 0.61, with standard deviation of 4- 0. 124.
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