Comparison of cadmium and enzyme-catalyzed nitrate reduction for determination of NO2-/NO3- in breath condensate.

Background: Analysis of NO2-/NO3- in expired breath condensate (EBC) has been proposed as a marker of inflammation in various lung diseases.

Methods: NO2- and total NO3-/NO2- concentrations were determined in EBC collected from healthy and asthmatic subjects. The NO3- was first reduced to NO2-, and total NO2- was detected by colorimetric Griess reaction. Two methods of NO3- reduction were compared. To reduce NO3-, cadmium (600 microl EBC-macromethod) and enzyme-NADPH-nitrate reductase (60 microl EBC-micromethod) were used.

Results: Macromethod: Mean NO2- concentrations in EBC were 1.64 +/- 0.24 micromol/l in healthy subjects and 0.42 +/- 0.17 micromol/l in asthmatic patients. Mean total NO2-/NO3- levels were 3.64 +/- 0.43 micromol/l in healthy subjects and 3.27 +/- 0.34 micromol/l in asthmatic. Micromethod: NO2- level: 1.69 +/- 0.23 micromol/l in healthy subjects and 0.53 +/- 0.21 micromol/l in asthmatics. Total NO2-/NO3- levels: 3.56 +/- 0.37 micromol/l in healthy subjects and 3.57 +/- 1.17 micromol/l in asthmatics. Variability index was 27% and 6% for macro- and micromethod, respectively. Recovery of NO3- added to EBC was 100% for enzymatic and almost 88% for cadmium reduction. There was no correlation between total NO2-/NO3- levels determined by macro- and micromethod.

Conclusions: We recommend enzymatic reduction as a better method for NO3- determination in EBC.