Abnormal Diurnal Rhythm of Urine Output Following Renal Transplantation: The Impact of Blood Pressure and Diuretics

Background. Nocturnal polyuria is the excretion at night of an excessive volume of urine. A major problem following renal transplantion is an abnormal diurnal rhythmicity in urine output. The purpose of this study was to elucidate the prevalence of nocturnal polyuria among renal transplant recipients in the early period after transplantation as well as at least 1 year after transplantation. We aimed to explore possible pathophysiological mechanisms behind nocturnal polyuria in this group of patients, focusing on the impact of blood pressure and medication. Methods. Seventeen recently transplanted patients 17 late transplant recipients, and 17 healthy controls were included in the study. Voiding habits were assessed by completion of a frequency-volume chart recording all fluid intakes and voiding. A concomitant 24-hour blood pressure profile was obtained in all. Results. Renal transplant recipients had a high prevalence of nocturnal polyuria (74%) and a disturbed blood pressure profile with a lack of appropriate nocturnal dipping (P < .0001) compared to controls. We found a positive correlation between increased nocturnal blood pressure and urine output at night (r = .368, P = .008). Patients taking diuretics had a circadian diurnal rhythm of urine output and a blood pressure profile similar to controls. Conclusions. Nocturnal polyuria was very common among both recent and late transplant recipients. A high fluid intake during daytime and hypervolemia were suggested as causes of a disturbed blood pressure profile, which partly seemed to explain the high urine output at night. Daytime diuretics may be an effective treatment of this inconvenient complication.