Breath-holding and tidal breathing nasal NO to screen children for Primary Ciliary Dyskinesia

Nasal nitric oxide (nNO) measurement is recommended to screen for Primary Ciliary Dyskinesia (PCD) in subjects with suggestive history and symptoms. Clinical use of alternative methods (i.e., breath-hold [BH], tidal breathing [TB]) in children unable to perform the gold standard slow Exhalation against a Resistance (ER) method has not been sufficiently evaluated. We extracted retrospectively (2013-2019) 454 files (374 subjects) containing nNO results. Median [IQR] age at inclusion was 7.0 [4.7-11.0] years, 105 (28.1%) children were younger than 5 years. ER or BH methods were more frequently mastered by children older than 5 years compared to younger children (69.4% and 52.7% vs. 21% and 5.6%, respectively; p < .0001), the latter succeeding only in TB measurement in 77.4% of cases. In 130 files with both ER and BH measurements (nNO-ER and nNO-BH), nNO-BH was 102 [96.2; 108.3]% that of nNO-ER. In 175 files including nNO-ER and nNO-TB measurements, nNO-TB was 64.4 [IQR: 53.7; 80.4]% that of nNO-ER with an excellent correlation between nNO values (r = .94 [95% CI 0.91; 0.95]; p < .0001) and discordance in the interpretation of nNO results in 16 (10.2%) cases. Final PCD diagnosis was similar in patients included before or after 5 years of age (confirmed 16 (15.2%) and 48 (17.8%); excluded 81 (77.1%) and 192 (71.4%), respectively; p = .32). In conclusion, reliable nNO-BH and nNO-ER results are interchangeable. Children tested with ER or with TB method have similar final PCD diagnosis. Alternative methods to measure nNO might be studied further for use in clinical practice.