 This study found that nasal nitric oxide, NNO, measurements are commonly used in the diagnosis of primary ciliary dyskinesia, PCD, in children, however there is significant variation in how the tests are performed and interpreted. Most centers measure NNO in children, with many measuring it before the age of 5 years old. Additionally, most centers perform NNO measurements during exhalation against a resistance or during tidal breathing, while some centers use only one method. Furthermore, the cut-off values used to distinguish between healthy and PCD patients vary significantly between centers, with some reporting results as an output, NL.min1, and others reporting them as parts per billion, PPP. This study highlights the need for greater standardization of NNO testing, including training and equipment, in order to ensure consistency and accuracy in diagnosing PCD. This article was authored by Nicole Badon, Thomas Ferkel, Amanda Lee Harris, and others.