title: Circadian variations of urinary electrolyte concentrations in preterm and term infants.
abstract: OBJECTIVE
  To determine whether a circadian variation of urinary excretion of calcium and phosphorus exists in preterm infants.
  
  
  METHODS
  We studied 70 newborn infants (median birth weight 1920 gm, range 660 to 3550 gm; median gestational age 34 weeks, range 25 to 42 weeks) at a median postmenstrual age of 36 weeks (range 32 to 42 weeks). Within a period of 24 hours, four urine specimens were collected during 6-hour periods. The concentrations of calcium, phosphorus, sodium, potassium, and creatinine were determined and creatinine quotients were calculated for each specimen.
  
  
  RESULTS
  No clinically relevant circadian variation in urinary excretion for any of these minerals was found.
  
  
  CONCLUSIONS
  If spot urine specimens are used to monitor calcium and phosphorus balance in preterm infants, the time of the day these are collected is not important.
authors.affiliation: Division of Neonatology and Pediatric Critical Care Medicine, Children's Hospital, University of Ulm, Germany.
authors.forename: A
authors.initials: A
authors.lastname: Trotter
authors.forename: M
authors.initials: M
authors.lastname: Stoll
authors.forename: J U
authors.initials: JU
authors.lastname: Leititis
authors.forename: A
authors.initials: A
authors.lastname: Blatter
authors.forename: F
authors.initials: F
authors.lastname: Pohlandt
mesh_terms: D002940:Circadian Rhythm / Q000502:physiology*; D004573:Electrolytes / Q000652:urine*; D006801:Humans; D007231:Infant, Newborn; D007234:Infant, Premature
chemical_list: D004573:Electrolytes