Experience Of Measuring Nasal Nitric Oxide (Nno) In A National Primary Ciliary Dyskinesia (Pcd) Centre (2006-20)

Background: nNO, alongside clinical history, is established in PCD screening. We describe our experience measuring nNO across the age range comparing methods, analysers, PCD diagnostic status & outliers. Methods: 856 patients (0.4-82.8yrs) referred to Southampton had nNO measured. Technically acceptable measurements were obtained using chemiluminescent analysers Niox Flex (2006-14)/ Ecomedics CLD88sp (2014-20) or electrochemical analysers Niox Mino (2013-17)/ Niox Vero (2017-2020). Cut-off 77nL/min was used for all measurements although this is defined only for velum closure, chemiluminescent measurements. Diagnostic status followed ERS Diagnostic Guideline (2016). Results: 9/113 (8%) positive patients had normal nNO. 17% of patients who were diagnosed ‘PCD unlikely’ had nNO <77nL/min. We obtained reproducible measurements in 110 children <5years (21 nasal tidal breathing (TB); 81 pursed lip TB, 8 breath hold). There is no cut off for these manoeuvres, but we found higher values helpful to add confidence that PCD is unlikely. CLD88sp & Vero provided acceptable velum closure measurements but were more difficult for patients to achieve on Vero. Pursed lip TB was acceptable using both instruments allowing for measurement in younger children. Nasal TB can be measured using CLD88sp. Conclusions: nNO is a good screening tool for PCD but should not be used diagnostically alone. nNO can be measured across age range on CLD88 & Vero with age appropriate method. nNO <5yrs may be useful to screen for PCD. Standardisation & predictive cut-offs need to be established for different manoeuvres and ages. Historical data review against current standards may highlight missed cases.