da Fonseca-Wollheim F
Zentrallaboratorium, Krankenhaus Zehlendorf, Berlin, Germany.
Eur J Clin Chem Clin Biochem. 1995 May;33(5):289-94. doi: 10.1515/cclm.1995.33.5.289.
The pH-dependent distribution of ammonia between blood cells and plasma was investigated with oxygenated blood samples from healthy subjects at 37 degrees C. Blood pH was varied between 6.95 and 7.65 by equilibration with different CO2 mixtures. Plasma ammonia concentrations were measured directly with a specific enzymatic method. Ammonia concentrations within blood cells were calculated from a) the concentration changes of ammonia in plasma after addition of 87.7 mumol/l NH4Cl to whole blood and b) the pH-dependent haematocrit. The pH-dependency of the distribution ratio(ammonia) = P-ammonia/cell ammonia (substance concentrations in water spaces) is described by the equation distribution ratio(ammonia) = 3.095 - 0.342 x pHplasma (r = 0.928, n = 36) in good agreement with available literature data on the distribution of H+. A quantitative figure to describe the actual NH4+ concentration in oxygenated whole blood at defined values of P-NH4+, P-pH and haematocrit is given. Values of distribution ratio(ammonia) at pH 7.4 (0.57 or 0.75, ammonia concentrations corrected/not corrected for water content) are higher than those assumed so far in the literature. Addition of non-permeating anions (citrate, EDTA) to whole blood results in a shift of NH4+ from the intra- to the extracellular compartment. In contrast, chaotropic anions like iodide or thiocyanate lower distribution ratio(ammonia). To avoid medically important bias in the measurement of plasma ammonia concentration, the changes in pH or in the ionic composition of the blood sample following pretreatment with anticoagulants or preservatives should not exceed certain limits. Citrate is not a suitable anticoagulant.
在37℃条件下，使用健康受试者的氧合血样研究了血细胞与血浆之间氨的pH依赖性分布。通过与不同的二氧化碳混合物平衡，使血液pH在6.95至7.65之间变化。血浆氨浓度采用特定的酶法直接测量。血细胞内的氨浓度根据以下计算得出：a）向全血中添加87.7 μmol/l氯化铵后血浆中氨的浓度变化，以及b）pH依赖性血细胞比容。分布比（氨）=血浆氨/细胞氨（水相中的物质浓度）的pH依赖性由方程分布比（氨）= 3.095 - 0.342×血浆pH（r = 0.928，n = 36）描述，这与关于H⁺分布的现有文献数据高度一致。给出了一个定量数据，用于描述在特定的血浆 - 氨、血浆pH和血细胞比容值下，氧合全血中实际的NH₄⁺浓度。pH 7.4时的分布比（氨）值（0.57或0.75，氨浓度已校正/未校正水含量）高于迄今为止文献中假设的值。向全血中添加非渗透性阴离子（柠檬酸盐、乙二胺四乙酸）会导致NH₄⁺从细胞内转移到细胞外。相反，促变性阴离子如碘化物或硫氰酸盐会降低分布比（氨）。为避免在血浆氨浓度测量中出现医学上重要的偏差，使用抗凝剂或防腐剂预处理后血样的pH或离子组成变化不应超过一定限度。柠檬酸盐不是一种合适的抗凝剂。
