Nocturnal polyuria has been well known in renal insufficiency. Recently, we found that as renal function deteriorated in chronic kidney disease (CKD), natriuresis was enhanced during the night with nocturnal blood pressure elevation. In the present study, we investigated whether nocturnal polyuria in CKD was due to the inability to concentrate urine, as previously proposed, or based on osmotic diuresis mainly by natriuresis.Methods
In 27 CKD patients, circadian rhythms of urinary sodium, potassium, urea and osmolar excretion rates (UNaV, UKV, UureaV, UosmV) as well as of urinary volume (V) and free-water clearance (CH2O) were estimated during both daytime (6:00 to 21:00) and nighttime (21:00 to 6:00). Then, the night/day ratios of these parameters were analysed in relation to creatinine clearance (Ccr) as a marker of glomerular filtration rate.Results
Ccr had significantly negative relationships with night/day ratios of V (R=−0.69; P < 0.0001), UosmV (R=−0.54; P=0.004) and UNaV (R=−0.63; P=0.0005), but no correlation with night/day ratios of CH2O (R=−0.33; P=0.1), UKV (R=−0.29; P=0.1) or UureaV (R=−0.31; P=0.1). Linear and multiple regression analysis identified nocturnal natriuresis rather than urea excretion as an independent determinant of nocturia.Conclusion
As renal function deteriorated, nocturnal polyuria was seen, being consistent with classical recognition. Furthermore, this increase in nocturnal urine volume seemed related to osmotic diuresis mainly by natriuresis rather than to water diuresis or urea excretion.