• Niek F Casteleijn, Debbie Zittema, Stephan J L Bakker, Wendy E Boertien, Carlo A Gaillard, Esther Meijer, Edwin M Spithoven, Joachim Struck, and Ron T Gansevoort.
• Department of Nephrology, University Medical Center Groningen, University of Groningen, Groningen, The Netherlands.
• Am. J. Nephrol. 2015 Jan 1; 41 (3): 248-56.

BackgroundVasopressin plays an essential role in osmoregulation, but has deleterious effects in patients with ADPKD. Increased water intake to suppress vasopressin activity has been suggested as a potential renoprotective strategy. This study investigated whether urine and plasma osmolality can be used as reflection of vasopressin activity in ADPKD patients.MethodsWe measured urine and plasma osmolality, plasma copeptin concentration, total kidney volume (TKV, by MRI) and GFR ((125)I-iothalamate). In addition, change in estimated GFR (eGFR) during follow-up was assessed.ResultsNinety-four patients with ADPKD were included (56 males, age 40 ± 10, mGFR 77 ± 32 ml/min/1.73 m(2), TKV 1.55 (0.99-2.40) l. Urine osmolality, plasma osmolality and copeptin concentration were 420 ± 195, 289 ± 7 mOsmol/l and 7.3 (3.2-14.6) pmol/l, respectively. Plasma osmolality was associated with copeptin concentration (R = 0.54, p < 0.001), whereas urine osmolality was not (p = 0.4). In addition, urine osmolality was not associated with TKV (p = 0.3), in contrast to plasma osmolality (R = 0.52, p < 0.001) and copeptin concentration (R = 0.61, p < 0.001). Fifty-five patients were followed for 2.8 ± 0.8 years. Baseline plasma and urine osmolality were not associated with change in eGFR (p = 0.6 and p = 0.3, respectively), whereas baseline copeptin concentration did show an association with change in eGFR, in a crude analysis (St. β = -0.41, p = 0.003) and also after adjustment for age, sex and TKV (St. β = -0.23, p = 0.05).ConclusionsThese data suggest that neither urine nor plasma osmolality are valid measures to identify ADPKD patients that may benefit from increasing water intake. Copeptin appears a better alternative for this purpose.© 2015 S. Karger AG, Basel.

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