TY - JOUR T1 - Debating the definition of airflow obstruction: time to move on? JF - European Respiratory Journal JO - Eur Respir J SP - 527 LP - 528 DO - 10.1183/09031936.00103309 VL - 34 IS - 3 AU - M. R. Miller AU - O. F. Pedersen AU - R. Pellegrino AU - V. Brusasco Y1 - 2009/09/01 UR - http://erj.ersjournals.com/content/34/3/527.abstract N2 - The clinical practice of medicine involves accurate history taking and appropriate clinical examination, followed by the formulation of possible diagnoses to account for the patient's condition. This usually leads to investigations being undertaken to confirm or refute the possible diagnoses. These investigations may be of a visual nature, such as imaging (radiology, magnetic resonance imaging or ultrasound) or endoscopy, or may be the measurement of physiological indices, such as blood pressure, height, weight, lung function or measurements from blood tests. For most measurements, clinicians are used to the concept of accepted normal ranges, which may be different for males and females. These ranges may be quite distinct and relatively invariable. For other measurements the situation is less clear, e.g. blood pressure, for which the acceptable ranges may be defined by their relationship to survival and risk of adverse outcome 1. In lung function tests, the normal ranges have usually been obtained from healthy nonsmoking subjects and are dependent on a number of other aspects related to the individual subject in question, namely their age, sex, height and ethnic background 2. This complicates the way in which a clinician can quickly interpret whether a subject's result is abnormal. The American Thoracic Society/European Respiratory Society task force on the standardisation of lung function testing has recommended that a given test is said to be abnormal when the measured value is below the lower limit of normality (LLN), defined as 1.645 standard deviations below predicted 3. However, an alternative way to define a lower limit for deciding on the presence of airflow obstruction for chronic obstructive pulmonary disease (COPD), based on the ratio of forced expiratory volume in 1 s (FEV1) to forced … ER -