Circadian Rhythms in Water and Solute Handling in Adults with a Spinal Cord Injury

Purpose: We evaluated nocturnal urine production and circadian rhythms of renal function (glomerular filtration, and water and solute diuresis) in adults with spinal cord injury compared to controls. Materials and Methods: This prospective observational study was done at Ghent University Hospital, Belgium. Participants were asked to perform a 24-hour urine collection. A blood sample was taken to calculate the diuresis rate and the renal clearance of creatinine, free water, solutes, sodium and urea. Results: A total of 119 patients were divided into 32 with spinal cord injury, and 68 controls with and 19 without nocturnal polyuria. Spinal cord injured patients showed no circadian rhythms in the diuresis rate or in the renal clearance of creatinine, free water, solutes, sodium or urea. Controls without nocturnal polyuria reported a lower nighttime diuresis rate and lower nighttime clearance of creatinine, solutes, sodium and urea compared to daytime levels. Controls with nocturnal polyuria had no circadian rhythms in the diuresis rate or creatinine clearance and a significant increase in nocturnal free water clearance compared to daytime levels. Conclusions: Comparing the mechanisms underlying nocturnal urine production between patients with spinal cord injury and controls revealed important differences. Spinal cord injured patients showed absent circadian rhythms in the renal clearance of creatinine (glomerular filtration), free water (water diuresis) and solutes such as sodium and urea (solute diuresis). Future research must be done to evaluate the role of patient stratification to find the most effective and safe treatment or combination of treatments for spinal cord injured patients with complaints or complications related to nocturnal polyuria.