TY - JOUR T1 - Why is COPD phenotyping like sorting diamonds? JF - European Respiratory Journal JO - Eur Respir J SP - 277 LP - 279 DO - 10.1183/09031936.00091214 VL - 44 IS - 2 AU - Peter G. Gibson AU - Vanessa M. McDonald Y1 - 2014/08/01 UR - http://erj.ersjournals.com/content/44/2/277.abstract N2 - The importance and management of asthma–chronic obstructive pulmonary disease overlap syndrome (ACOS) is a topic of lively debate and, until recently, there have been very few data related to this topic that could be used to inform guidelines and practice. Indeed, whether or not ACOS exists and whether it matters is central to this debate.We can all recognise pure cases of asthma and chronic obstructive pulmonary disease (COPD) by their well-described clinical and pathological features. These “gems” are regularly presented as being typical of the disease, with differentiation between asthma and COPD promoted as a key goal of clinical diagnostics [1, 2]. What we have been slow to accept are cases where the differentiation is not clear because of overlapping clinical features that manifest as “impurities” in the diagnosis. It now turns out that these diagnostic impurities are the rule rather than the exception.The same can be found with diamonds. We all value a pure gem and diamond experts measure this as a property called clarity. Clarity is graded by major societies on a scale from flawless to imperfect, a bit like our peer-review system really. Only about 20% of all diamonds have a clarity grading that is high enough for the diamond to be “diagnosed” as a gemstone; the other 80% are relegated to industrial use only. Of that top 20%, the harder you look, the more impurities you find.So is the situation with airway disease. Pure cases of asthma or COPD are the minority [3] but it is this paradigm that is prized by our teachers and opinion leaders. In the older age group, the majority of cases that are seen in day-to-day clinical practice (i.e. industrial) have impure clinical features. While diamond experts have a clear and systematic approach … ER -