AQP2 and chronic kidney disease: We performed a post hoc sub analysis of u-NKCC2, uAQP2 and u-ENaCγ dividing patients with CKD into GFR ≤ 30 ml/min/1.73 m2 i.e. stage IV (n = 11; mean GFR: 21 ml/min/1.73 m2) and GFR > 30 ml/min/1.73 m2 i.e. stage III (n = 9; mean GFR: 48 ml/min/1.73 m2) (Figure 3D-F).Patients with CKD stage IV had a higher u-AQP2, at baseline, than CKD stage III and u-AQP2 remained significantly higher throughout the examination day (Figure 3D).