• Bronchiectasis
• cystic fibrosis
• immunodeficiency
• paediatric asthma
• paediatric lung disaese
• rare lung diseases

Once upon a time, many diagnoses were easy—for example, if you had a high sweat chloride, you had cystic fibrosis (CF); if the sweat electrolytes were normal, you did not. Now, recent advances in molecular genetics and airway electrophysiology have pushed back and blurred the diagnosis of CF, such that what was once straightforward can in atypical cases become the source of endless debate. The same has become true in primary ciliary dyskinesia (PCD). The situation in PCD is even more complicated; diagnosis seldom relied on a single test, but has become confusing because of the large number of tests currently available, many of which are very sophisticated and only available in a small number of centres. So, what is a PCD diagnosis in the 21st century?

First, of course, is it necessary to make a specific diagnosis of PCD at all? There are several reasons why it is; the treatment of upper airway disease in PCD is counterintuitive1 and there are genetic implications both for PCD and other parts of the expanding ciliopathy spectrum for the families. Importantly, there are no big randomised controlled trials of treatment in PCD; most treatments are extrapolated from protocols used for CF, a disease with completely different pathophysiology (reduced airway surface liquid rather than primary ciliary dysmotility). So, if this deficiency is to be addressed, the accurate diagnosis of PCD is a prerequisite. The same is also true for studies in basic mechanisms, including finding novel PCD genes.

There is wide variation in availability of the different tests across Europe2; the range is summarised in table 1. There is no one …