Moshage H, Kok B, Huizenga J R, Jansen P L
Department of Medicine, University Hospital Groningen, The Netherlands.
Clin Chem. 1995 Jun;41(6 Pt 1):892-6.
Plasma nitrite and nitrate determinations are increasingly being used in clinical chemistry as markers for the activity of nitric oxide synthase and the production of nitric oxide radicals. However, a systematic evaluation of the determination of nitrite and nitrate in plasma has not been performed. In this study the recovery and stability of nitrite and nitrate in whole blood and in plasma, the relation between nitrite and nitrate concentrations in plasma, and possible sources of artifacts were investigated. The main conclusions are: (a) Recovery of nitrite and nitrate from plasma is near-quantitative (87%) and reproducible; (b) nitrite and nitrate are stable in (frozen) plasma for at least 1 year; (c) nitrite in whole blood is very rapidly (> 95% in 1 h) oxidized to nitrate, and therefore plasma nitrite determination alone is meaningless; (d) the ranges of nitrite and nitrate concentrations in plasma samples of 26 healthy persons are 1.3-13 mumol/L (mean 4.2 mumol/L) and 4.0-45.3 mumol/L (mean 19.7 mumol/L), respectively; (e) plasma nitrite and nitrate concentrations were not correlated (nitrite as % of total nitrite + nitrate varied from 3.9% to 88% in plasma samples); and (f) plasma samples should be deproteinized, and background controls for each sample should be included in the assay, to avoid measuring artifactually high nitrite and nitrate concentrations in plasma.
血浆中亚硝酸盐和硝酸盐的测定在临床化学中越来越多地被用作一氧化氮合酶活性和一氧化氮自由基生成的标志物。然而，尚未对血浆中亚硝酸盐和硝酸盐的测定进行系统评估。在本研究中，对全血和血浆中亚硝酸盐和硝酸盐的回收率及稳定性、血浆中亚硝酸盐和硝酸盐浓度之间的关系以及可能的假象来源进行了研究。主要结论如下：(a) 血浆中亚硝酸盐和硝酸盐的回收率接近定量（87%）且可重复；(b) 亚硝酸盐和硝酸盐在（冷冻）血浆中至少1年内稳定；(c) 全血中的亚硝酸盐会非常迅速地（1小时内>95%）氧化为硝酸盐，因此仅测定血浆亚硝酸盐没有意义；(d) 26名健康人血浆样本中亚硝酸盐和硝酸盐浓度范围分别为1.3 - 13 μmol/L（平均4.2 μmol/L）和4.0 - 45.3 μmol/L（平均19.7 μmol/L）；(e) 血浆中亚硝酸盐和硝酸盐浓度不相关（血浆样本中亚硝酸盐占总亚硝酸盐 + 硝酸盐的百分比从3.9%到88%不等）；(f) 血浆样本应进行去蛋白处理，并且测定中应包含每个样本的空白对照，以避免测定血浆中亚硝酸盐和硝酸盐浓度出现人为偏高的情况。
