Identifying the main predictors of urine output in autosomal-dominant polycystic kidney disease (ADPKD) patients taking tolvaptan

Abstract

Background: Few works have analyzed factors associated with urine output in ADPKD patients taking tolvaptan (TVP).

Methods: We selected 24-h urine samples from ADPKD patients treated with TVP. Urine osmolality/creatinine ratio was used as estimator of urinary osmolar load.

Results: We included 127 urine samples from 61 patients. After TVP, urine output doubled with a parallel reduction in urine solute concentration. However, when expressed as urine solute/creatinine ratios, no significant changes were observed. Daily osmolar load and osmolality/creatinine ratio did not change significantly. Before TVP, urine output was positively correlated with body weight and urine osmolality/creatinine ratio and negatively with eGFR, urine morning osmolality, and 24-h urine-calculated osmolality. After TVP, urine output was positively correlated with body weight, eGFR and negatively with age. There was a poor correlation with urine-calculated osmolality. We constructed a predictor model using mixed-effects modeling and we found that urine output was related to lower age, higher body weight, higher eGFR, and greater doses of TVP. When body weight was removed, urine output was also related to male sex and a higher daily osmolar excretion. Equation of prediction was: Urine output (mL/day) = 2771-52.9 × Age (years) + 58.4 × Weight (kg) + 18.7 × eGFR (mL/min) + 870 (if TVP = 90/30 mg) + 517 (if TVP = 60/30 mg).

Conclusion: Patients taking TVP will undergo an increase about twice in urine production from baseline. Greater doses of TVP cause a progressive increase in urine production. GFR, age, and body weight are the main predictors of future urine output in patients taking TVP.

Keywords: Autosomal polycystic kidney disease; Glomerular filtration rate; Tolvaptan; Urine osmolar load; Urine output.