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Author(s): Mathias G. Holgersen [sup.1] , June K. Marthin [sup.1] , Kim G. Nielsen [sup.1] Author Affiliations: (Aff1) grid.475435.4, Danish PCD & chILD Centre, CF Centre Copenhagen, Paediatric Pulmonary Service, [...], Introduction Nasal nitric oxide (nNO) is extremely low in individuals with primary ciliary dyskinesia (PCD) and is recommended as part of early workup. We investigated whether tidal breathing sampling for a few seconds was as discriminative between PCD and healthy controls (HC) as conventional tidal breathing sampling (cTB-nNO) for 20-30 s. Methods We performed very rapid sampling of tidal breathing (vrTB-nNO) for 2, 4 and 6 s, respectively. Vacuum sampling with applied negative pressure (vrTB-nNO.sub.vac; negative pressure was applied by pinching the sampling tube) for < 2 s resulted in enhanced suction of nasal air during measurement. Feasibility, success rate, discriminatory capacity, repeatability and agreement were assessed for all four sampling modalities. Results We included 13 patients with PCD, median (IQR) age of 21.8 (12.2-27.7) years and 17 HC, 25.3 (14.5-33.4) years. Measurements were highly feasible (96.7% success rate). Measured NO values with vrTB-nNO modalities differed significantly from TB-nNO measurements (HC: p < 0.001, PCD: p < 0.05). All modalities showed excellent discrimination. The vacuum method gave remarkably high values of nNO in both groups (1865 vs. 86 ppb), but retained excellent discrimination. vrTB-nNO.sub.4sec, vrTB-nNO.sub.6sec and vrTB-nNO.sub.vac showed identical specificity to cTB-nNO (all: 1.0, 95% CI 0.77-1.0). Conclusion vrTB-nNO sampling requires only a few seconds of probe-in-nose time, is feasible, and provides excellent discrimination between PCD and HC. Rapid TB-nNO sampling needs standardisation and further investigations in infants, young children and patients referred for PCD workup.