Choice of nasal nitric oxide technique as first-line test for primary ciliary dyskinesia

Nasal nitric oxide (nNO) has a well-known potential as an indirect discriminative marker between patients with primary ciliary dyskinesia (PCD) and healthy subjects, but real-life experience and usefulness in young children is sparsely reported. Three nNO sampling methods were examined and compared as first-line tests for PCD. Healthy subjects, confirmed PCDs, consecutive referrals with PCD-like symptoms and patients with cystic fibrosis (CF) had nNO sampled during breath hold (BH-nNO), oral exhalation against resistance (OE-R-nNO) and tidal breathing (TB-nNO) aiming to expand age range into infancy. 282 subjects, 117 consecutive referrals, 59 PCDs, 49 CF patients and 57 healthy subjects, were included. All methods separated significantly between PCD and non-PCD, including CF with reliability, in ranking order BH-nNO > OE-R-nNO > TB-nNO. Acceptability in children ranked in reverse order. A problematic high fraction (39%) of false positive TB-nNO was found in young children. An unexpected large fraction (6.8%) of PCDs had nNO values above cut-off. nNO is a helpful first-line tool in real-life PCD work-up in all age groups if the sampling method is chosen according to age. nNO can be misleading in a few patients with true PCD. Further studies are strongly needed in young children.