CIRCADIAN VARIATIONS OF URINARY ELECTROLYTE CONCENTRATIONS IN PRETERMAND TERM INFANTS

Objectives: To determine whether a circadian variation of urinary excr etion of calcium and phosphorus exists in preterm infants. Study desig n: We studied 70 newborn infants (median birth weight 1920 gm, range 6 60 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). With in a period of 24 hours, four urine specimens were collected during 6- hour periods. The concentrations of calcium, phosphorus, sodium, potas sium, and creatinine were determined and creatinine quotients were cal culated for each specimen. Results: No clinically relevant circadian v ariation in urinary excretion for any of these minerals was found. Con clusion: If spot urine specimens are used to monitor calcium and phosp horus balance in preterm infants, the time of the day these are collec ted is not important.