title: Circadian variation of mineral and bone parameters in end-stage renal disease.
abstract: BACKGROUND
  Mineral and bone parameters are actively managed in end-stage renal disease (ESRD). However, whether these undergo circadian variation is not known. We investigated the circadian variation of mineral and bone parameters in patients on long-term hemodialysis.
  
  
  METHODS
  Seventeen ESRD patients on long-term hemodialysis and eight volunteers without kidney disease were enrolled. Subjects had all medications that affect calcium-phosphate-parathyroid hormone balance (phosphate binders, vitamin D analogues, and calcimimetics) discontinued. Thereafter, for a period of 5 days, subjects consumed a diet controlled in calcium (1,200 mg per day) and phosphorus (1,000 mg per day) content. On the sixth day (a non-dialysis day for the ESRD patients), enrollees underwent twelve 2-h blood draws for phosphate, ionized calcium, parathyroid hormone (PTH), total 25-hydroxy vitamin D (25OHD), and fibroblast growth factor-23 (FGF-23).
  
  
  RESULTS
  In the ESRD patients plasma phosphate demonstrated significant circadian variation (P < 0.00001). The peak occurred around 3:30 am and nadir occurred around 11:00 am. Ionized calcium (P = 0.0036), PTH (P = 0.0004) and 25OHD (P = 0.009) also varied significantly during the circadian period; for ionized calcium peak and nadir occurred around 12:15 pm and 8:00 pm, parathyroid hormone 5:45 pm and 10:15 am, and 25OHD 9:45 am and 4:00 pm respectively. FGF-23 did not show a significant circadian variation. Only phosphate (P < 0.0001) and PTH (P = 0.00008) demonstrated circadian variation in the control group.
  
  
  CONCLUSIONS
  Blood concentrations of phosphate, calcium, PTH and 25-hydroxy vitamin D, exhibit a circadian variation in patients with ESRD. Knowledge of these phenomena is pertinent for the interpretation of clinical testing.
authors.affiliation: Divisions of Nephrology, Department of Medicine, Medical College of Wisconsin, 9200 W. Wisconsin Ave., CLCC 5220, Milwaukee, WI, 53226, USA, haritriv7@gmail.com.
authors.forename: Hariprasad
authors.initials: H
authors.lastname: Trivedi
authors.forename: Aniko
authors.initials: A
authors.lastname: Szabo
authors.forename: Shi
authors.initials: S
authors.lastname: Zhao
authors.forename: Tom
authors.initials: T
authors.lastname: Cantor
authors.forename: Hershel
authors.initials: H
authors.lastname: Raff
mesh_terms: D000328:Adult; D015415:Biomarkers / Q000097:blood; D001842:Bone and Bones / Q000378:metabolism* / Q000503:physiopathology; D002118:Calcium / Q000097:blood; D016022:Case-Control Studies; D002940:Circadian Rhythm; D005260:Female; D000089703:Fibroblast Growth Factor-23; D005346:Fibroblast Growth Factors / Q000097:blood; D006801:Humans; D007676:Kidney Failure, Chronic / Q000097:blood* / Q000175:diagnosis / Q000503:physiopathology / Q000628:therapy; D008297:Male; D008875:Middle Aged; D010281:Parathyroid Hormone / Q000097:blood; D010710:Phosphates / Q000097:blood; D011237:Predictive Value of Tests; D006435:Renal Dialysis; D015203:Reproducibility of Results; D013997:Time Factors; D016896:Treatment Outcome; D014807:Vitamin D / Q000031:analogs & derivatives / Q000097:blood
chemical_list: D015415:Biomarkers; C000717427:FGF23 protein, human; C470125:PTH protein, human; D010281:Parathyroid Hormone; D010710:Phosphates; D014807:Vitamin D; D005346:Fibroblast Growth Factors; D000089703:Fibroblast Growth Factor-23; C104450:25-hydroxyvitamin D; D002118:Calcium