Urine and plasma osmolality in patients with autosomal dominant polycystic kidney disease: reliable indicators of vasopressin activity and disease prognosis?
BACKGROUND
Vasopressin 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.


METHODS
We 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.


RESULTS
Ninety-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).


CONCLUSIONS
These 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.
Department of Nephrology, University Medical Center Groningen, University of Groningen, Groningen, The Netherlands.
Niek F
NF
Casteleijn
Debbie
D
Zittema
Stephan J L
SJ
Bakker
Wendy E
WE
Boertien
Carlo A
CA
Gaillard
Esther
E
Meijer
Edwin M
EM
Spithoven
Joachim
J
Struck
Ron T
RT
Gansevoort
D000328:Adult; D015415:Biomarkers / Q000097:blood / Q000652:urine; D005260:Female; D005500:Follow-Up Studies; D005919:Glomerular Filtration Rate; D006020:Glycopeptides / Q000097:blood*; D006801:Humans; D008297:Male; D008875:Middle Aged; D009994:Osmolar Concentration; D016891:Polycystic Kidney, Autosomal Dominant / Q000097:blood* / Q000503:physiopathology / Q000652:urine*; D011379:Prognosis; D014667:Vasopressins / Q000097:blood*
D015415:Biomarkers; D006020:Glycopeptides; C048197:copeptins; D014667:Vasopressins