The influence of pCO2 on the rate of ammonia formation in blood.

The influence of the sample pCO2 on the rate of ammonia formation was studied with gas equilibrated blood samples, using different gas mixtures for the equilibration. The rate of increase in plasma ammonia concentration at a mean pCO2 of 62 mm Hg = 8.2 kPa (mean pH = 7.282) was significantly lower than at 36 mm Hg = 4.8 kPa (pH = 7.438). In CO2-depleted blood (pH > 8) ammonia formation was strongly accelerated. This was reversible by readjusting the pH to 7.4 by addition of Tris-HCl solution. In stoppered containers with or without enclosed atmospheric air, a decrease of blood pCO2 or an increase of pH values was not observed during storage over 15 minutes at 0 or 20 degrees C. Although this study confirms that the pCO2 (or rather the pH) is an important analytical influence quantity in the determination of plasma ammonia, strictly anaerobic processing of the blood samples is not necessary; the usual technique of transporting and preprocessing blood samples in partially filled and stoppered containers appears to be adequate. Mainly due to the deamination of intracellular AMP (1), the ammonia1) concentration in blood increases continuously after sampling. Rates of increase in plasma ammonia concentration have recently been investigated thoroughly with blood samples from healthy probands to define the maximum delay between sampling and separation of the blood cells that can be tolerated if the in vivo existing plasma ammonia concentration has to be measured (2). Strictly speaking, the guidelines for handling the blood samples (2) apply to blood stored under anaerobic conditions.(ABSTRACT TRUNCATED AT 250 WORDS)