In addition, it will be very interesting to measure serial FGF23 levels in COPD cohorts to obtain longitudinal FGF23 trajectories and correlate these with AECOPD frequency and mortality, since it has been shown that a subgroup of CKD patients with rising FGF23 levels has an exceptionally high risk of death [20]. Here, FGF23 is linked to chronic obstructive pulmonary disease.