Objectives: Premature babies require supplementation with calcium (Ca) and phosphorus (P) to prevent metabolic bone disease of prematurity. To guide mineral supplementation, 2 methods of monitoring urinary excretion of Ca and P are used: urinary Ca or P concentration and Ca/creatinine (Crea) or P/Crea ratios. We compare these 2 methods in regards to their agreement on the need for mineral supplementation.
Methods: Retrospective chart review of 230 premature babies with birth weight <1500 g, undergoing screening of urinary spot samples from day 21 of life and fortnightly thereafter. Hypothetical cutoff values for urine Ca or P concentration (1 mmol/L) and urine Ca/Crea ratio (0.5 mol/mol) or P/Crea ratio (4 mol/mol) were applied to the sample results. The agreement on whether to supplement the respective minerals based on the results with the 2 methods was compared. Multivariate general linear models sought to identify patient characteristics to predict discordant results.
Results: A total of 24.8% of cases did not agree on the indication for Ca supplementation, and 8.8% for P. Total daily Ca intake was the only patient characteristic associated with discordant results.
Conclusions: With the intention to supplement the respective mineral, comparison of urinary mineral concentration with mineral/Crea ratio is moderate for Ca and good for P. The results do not allow identifying superiority of either method on the decision as to which babies require Ca and/or P supplements.
*Division of Paediatric Nephrology, University Children's Hospital, Inselspital
†Institute for Evaluative Research in Medicine, University of Bern
‡Division of Neonatology, University Children's Hospital, Inselspital Bern, Bern, Switzerland.
Address correspondence and reprint requests to Eveline Staub, Division of Neonatology, University of Utah, 417 Wakara Way, Office 3117, Salt Lake City, UT 84108 (e-mail: firstname.lastname@example.org).
Received 9 November, 2013
Accepted 9 November, 2013
The authors report no conflicts of interest.