Nasal nitric oxide measurement for the diagnosis of primary ciliary dyskinesia: summary of the European Respiratory Society technical standard.

Nasal nitric oxide (nNO) measurement is important in the primary ciliary dyskinesia (PCD) diagnostic pathway because levels are consistently very low in most patients. Machine type, environmental factors, respiratory manoeuvres and report interpretation are fundamental considerations when performing nNO testing. A European Respiratory Society Task Force recently published standards for testing which we summarise and discuss in this article. There are two main types of nNO machines: chemiluminescence and electrochemical analysers. Chemiluminescence analysers are highly accurate, reliable, real-time and have been validated in multicentre studies but are less portable and more expensive to purchase and maintain in comparison to electrochemical devices. Several factors may influence nNO levels and need to be addressed during patient preparation for testing. Factors including acute viral infections and nose bleeds may contribute to falsely low nNO levels, whereas high ambient NO levels may falsely increase nNO. Tidal breathing, breath-hold and exhalation against resistance are the three main respiratory manoeuvres used in nNO sampling and require a minimal, modest and high level of patient cooperation respectively. Finally, standardised reporting of nNO testing and the correct interpretation helps clinicians to formulate an appropriate clinical plan towards an accurate PCD diagnosis.