Exhaled nitric oxide (FE_NO) is a reliable non-invasive marker of airway inflammation. In 2003 FE_NO chemiluminescence analyzer (NIOX^®; Aerocrine AB, Solna, Sweden) was approved by U.S. Food and Drug Administration for monitoring asthma therapy. Recently, the same company developed a portable device using electrochemical sensors (NIOX-MINO^®; Aerocrine AB). The aim of our study was to compare NIOX-MINO^® FE_NO values to those obtained by NIOX^® and to calculate a correction equation.

Two adequate measurements obtained by NIOX^® and NIOX-MINO^® were recorded in 32 subjects (16 females, mean age 41 years).

FE_NO values measured by NIOX-MINO^® were systematically higher than those obtained by NIOX^® (47.1ppb, IC 95% 35.2–59.1 and 36.9ppb, IC 95% 25.0–49.0, respectively). There was a significant correlation (r=0.998, p<0.001) between FE_NO measured by the two analyzers and the following conversion equation was calculated as:

FE_NO(NIOX^®)=−1.656(SE=0.61)+0.808(SE=0.009)× FE_{NO(NIOX-MINO^®)}

FE_NO values measured by the portable nitric oxide analyzer are reliable and strongly correlated with values obtained by the standard stationary device, with a systematic difference observed between the two instruments' values that can be described by the conversion equation we provided. This equation will help clinicians and researchers to compare data obtainable by the two analyzers.