Nasal nitric oxide screening for primary ciliary dyskinesia: systematic review and meta-analysis

Nasal nitric oxide (nNO) concentrations are low in patients with primary ciliary dyskinesia (PCD) providing a noninvasive screening test. We conducted a systematic review of the literature to examine the utility of nNO in screening for PCD, in particular 1) different respiratory manoeuvres during sampling (velum closure, tidal breathing, etc.), 2) accuracy in screening young/uncooperative children, 3) stationary versus portable analysers, and 4) nNO in "atypical" POD. 96 papers were assessed according to modified PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) criteria and 22 were included in this review. Meta-analysis of 11 studies comparing nNO during a velum closure breath hold gave a mean +/-SD nNO of 19.4+/-18.6 nL.min(-1) in PCD (n=478) and 265.0+/-118.9 nL.min(-1) in healthy controls (n=338). Weighted mean difference for PCD versus healthy controls was 231.1 nL.min(-1) (95% CI 193.3-268.9; n=338) and 114.1 nL.min(-1) (95% CI 101.5-126.8; n=415) for POD versus cystic fibrosis. Five studies of nNO measurement during tidal breathing demonstrated that this is an acceptable manoeuvre in young children where velum closure is not possible, but the discriminatory value was reduced. Four small studies of portable NO analysers suggest these are reliable tools for screening for POD. However, nNO must be interpreted alongside clinical suspicion. Future studies should focus on standardising sampling techniques and reporting.