Adaptation of the Nitrate Reductase and Griess Reaction Methods for the Measurement of Serum Nitrate plus Nitrite Levels

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Abstract
Nitrite and nitrate determinations in biological fluids are increasingly being used as markers of nitric oxide production. We have modified a nitrate reductase and Griess reaction method for the measurement of serum nitrate and nitrite in ultrafiltrated samples using a microtitre plate. The recoveries of nitrate and nitrite were 95% (range = 86–113%) and 100% (range = 92–109%), respectively. The intra and inter assay coefficients of variation for nitrate plus nitrite in the concentration range 40–50μM were 9·1% and 7·8%, and in the concentration range of 2·5–10μM 23·4% and 25·5%, respectively. At its lower limit the assay is able to detect 125 pmoles of nitrate plus nitrite in 50μL of sample (2·5μmol/L). A mean serum nitrate plus nitrite level of 32·8μmol/L (SD 12·3) was measured in 24 healthy adult volunteers (12 men and 12 women), no age or sex differences were noted.