This invention pertains to the discovery that Parathyroid Hormone-related Protein (PTHrP) can be detect and/or stage, and/or treat chronic lung diseases. In particular, it was discovered that PTHrP levels in broncho-alveolar lavage are indicative of lung "health" and "disease, and can be used to predict lung disease in patients at risk of chronic lung disease and/or to evaluate the efficacy of a ventilation regime.