Considerations and pitfalls in phenotyping and reclassification of chronic obstructive pulmonary disease.

As the clinical and research focus of chronic obstructive pulmonary disease (COPD) evolves from regarding obstructive lung disease as a single disease entity to recognizing the complexity of disease expression, the importance of COPD phenotyping rises to the forefront. The reclassification of COPD holds both prognostic and therapeutic implications but does not come without issues that may complicate classification efforts. In this review, we discuss the significance of refining the definition of the term phenotype, consider the impact of variations in cohort severity and attribute mix, account for the contrast of longitudinal vs cross-sectional cohort analysis, recognize the differing criteria used to define disease traits along with the nuances of combining cohorts, and identify the interaction of covariates as we advance in the field of COPD phenotyping.