Comparison of high-pressure liquid chromatography (HPLC) and Griess reagent-spectroscopic methods for the measurement of nitrate in serum from healthy individuals in the Nordic countries

Bioavailability of NO can be estimated by measuring the concentration of nitrate (NO3) in serum. However, the methods used for the measurement NO3 in plasma or serum show a great degree of variation. Therefore, we compared two analytical methods for the measurement of NO3 in serum. Design and methods The concentration of NO3 in 600 serum samples collected from healthy individuals was determined by the HPLC and by the Griess reagent-spectroscopic method. Results The concentration of NO3 in the samples was 29.4 ± 16.1 μmol/L and 26.2 ± 14.0 μmol/L (mean ± SD) measured by HPLC and Griess reagent-spectroscopic method respectively (p < 0.0001). We detected a significant correlation between the two methods (R = 0.81, p < 0.0001). Conclusions A significant correlation between the two methods may suggest that either method can be used for the measurement of NO3 in serum, however the Griess reagent-spectroscopic method measures lower concentrations of NO3 than the HPLC method.