Purpose of review: In the evaluation of patients with interstitial lung diseases (ILD), treatment decisions made by clinicians, including referral for lung transplant, are based on disease severity assessment. It is crucial to quantify disease severity and numerous attempts were made to find a reliable prognostic assessment method.

Recent findings: Research focused on which severity thresholds should be used to identify patients at higher risk of death and, more recently, on prognostic composite physiologic indices and staging systems, which compared with single variables offer a number of advantages. Composite indices, such as the composite physiologic index, provide a more accurate overall estimate of disease severity and account for confounding coexisting disease process, such as pulmonary hypertension and emphysema. In idiopathic pulmonary fibrosis clinical measures have been integrated in the GAP model that strongly correlates with disease severity and mortality. Recently, the GAP model derived for idiopathic pulmonary fibrosis (IPF) has been successfully applied to non-IPF fibrotic ILD.

Summary: The heterogeneity in ILDs related to both disease and patient-specific factors, for many years, has impeded progress in the development of a reliable method to quantify disease severity. In the last decade, novel composite physiologic indices and staging systems have been shown to accurately reflect disease severity and reliably predict survival. Moreover, the recent finding of one informative staging system applicable to different subgroups of ILD patients has the potential to radically transform both clinical practice and research strategy in the near future of ILD.