The NIOX MINO^® is a nitric oxide (FE_NO) analyser based on electrochemical technology. It includes a replaceable sensor. Quality control procedures are recommended, but regular calibration is not possible. We aimed to evaluate the performance characteristics of the NIOX MINO^® to identify if reproducibility changed over time, or with different sensors. Also, there are reports that reproducibility of FE_NO may be reduced in patients with high FE_NO: our secondary aim was to address this issue.

Reproducibility in 24 separate sensor-analyser units was calculated on three occasions over two months in 17 patients. These included 9 patients whose FE_NO was high (mean 80 ppb) and 8 in whom FE_NO was low (mean 16 ppb).

One device failed quality control testing. For the remaining 23 sensor-analyser combinations, the mean coefficient of variation was 4.0% (range 1.2–7.2%) at baseline, 3.6% (range 2.0–7.0) at one month, and 3.6% (range 1.6–7.6%) at two months. The 95% C.I. for the mean limits of agreement for FE_NO was ±4.2 ppb (range 0.9–9.6 ppb), ±3.8 ppb (range 1.6–6.9 ppb) and ±3.2 ppb (range 1.2–6.8 ppb) respectively (NS). The limits of agreement exceeded the manufacturer’s specifications (±5 ppb) in 0 devices at baseline, 3 (13%) at one month, and 5 (22%) at two months.

Reproducibility of FE_NO using the NIOX MINO^® was within clinically acceptable limits (±10 ppb) and was generally stable. However, with time, a proportion of individual sensor-analyser combinations yielded variability outside the manufacturer’s specifications.