Assessment of the place of tubular reabsorption of phosphorus in the diagnosis of osteopenia of prematurity

Aim: In this study, we aimed to investigate the utility of tubular reabsorption of phosphorus in the diagnosis of osteopenia of prematurity in addition to biochemical markers. Material and Methods: Premature babies with a gestational age of <= 32 weeks and/or a birth weight of <= 1 500 g who were hospitalized in the neonatal intensive care unit between June 2009 and March 2011 were included in the study. These babies were evaluated at the 40th gestational week and serum calcium, phosphorus, alkaline phosphatase, urea, creatinine, urinary calcium and phosphorus levels were measured and tubular reabsorption of phosphorus was determined. The subjects who had bone graphy findings and/ or an alkaline phosphatase level of >400IU/L and a phosphorus value of <3.5 mg/dL were considered osteopenic. The levels of tubular reabsorption of phosphorus of the osteopenic patients were compared with the ones of the non-osteopenic patients. The study was initiated after obtaining ethics committee approval (date: 04.29.2009/213). Results: During the study period, a total of 698 premature babies were hospitalized in our neonatology unit. A diagnosis of osteopenia of prematurity was made in 24 of 190 subjects who met the study criteria. The level of tubular reabsorption of phosphorus was compared with the serum calcium, phosphorus and alkaline phosphatase levels measured at the 40th gestational week and alkaline phosphatase was found to be significantly increased in the group with a high tubular reabsorption of phosphorus (>=%95). When the subjects with a phosphorus level of <3.5 mg/dL and an alkaline phosphatase level of >499 IU were compared with the newborns who were found to have a tubular reabsorption of phosphorus of >=%95 for the objective of evaluating the specificity and sensitivity of tubular reabsorption of phosphorus, the sensitivity, specificity, positive predictive value and negative predictive value of tubular reabsorption of phosphorus in the diagnosis of osteopenia were found to be 27%, 82%, 17% and 89%, respectively. When the osteopenic and non-osteopenic patients were compared in terms of the levels of tubular reabsorption of phosphorus, no statistically significant difference was found. Conclusions: It was thought that it was not appropriate to use tubular reabsorption of phosphorus alone in the diagnosis of osteopenia of prematurity.