Location: Children's Nutrition Research CenterTitle: High frequencies of elevated alkaline phosphatase activity and rickets exist in extremely low birth weight infants despite current nutritional support Author
Submitted to: BMC Pediatrics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/29/2009
Publication Date: 7/29/2009
Publication URL: http://www.biomedcentral.com/1471-2431/9/47
Citation: Mitchell, S.M., Rogers, S.P., Hicks, P.D., Hawthorne, K.M., Parker, B.R., Abrams, S.A. 2009. High frequencies of elevated alkaline phosphatase activity and rickets exist in extremely low birth weight infants despite current nutritional support. BMC Pediatrics. 9:47. Interpretive Summary: Despite vitamin and mineral supplementation, small premature infants commonly suffer from weak bones, which give rise to osteopenia and rickets. Our objectives in this study were to evaluate our experience with the diagnosis of rickets in these infants. We evaluated all infants who were less than 2.2 pounds at birth who were admitted to a local hospital in 2006 and 2007. We found that a blood test called the total alkaline phosphatase activity (APA) was abnormally high in many of these infants. The birth weight of the infants was significantly inversely related to both this blood test and to findings of weak bones (rickets) on X-rays. Given the very high risk of osteopenia and rickets among small premature infants, we recommend consideration of early screening and early mineral supplementation, especially among infants less than 1 pound 5 ounces at birth. This may help lessen the risk of severe bone loss while the infants are growing.
Technical Abstract: Osteopenia and rickets are common among extremely low birth weight infants (ELBW, <1000 g birth weight) despite current practices of vitamin and mineral supplementation. Few data are available evaluating the usual course of markers of mineral status in this population. Our objectives in this study were to determine the relationship between birth weight (BW) and peak serum alkaline phosphatase activity (P-APA) in ELBW infants, and evaluate our experience with the diagnosis of rickets in these infants. We evaluated all ELBW infants admitted to Texas Children's Hospital NICU in 2006 and 2007. Of 211 admissions, we excluded 98 patients who were admitted at >30 days of age or did not survive/stay for >6 weeks. Bone radiographs obtained in 32 infants were reviewed by a radiologist masked to laboratory values. In this cohort of 113 infants, P-APA was found to have a significant inverse relationship with BW, gestational age and serum phosphorus. In paired comparisons, P-APA of infants <600 g (957 +/- 346 IU/L, n = 20) and infants 600–800 g (808 +/- 323 IU/L, n = 43) were both significantly higher than P-APA of infants 800–1000 g (615 +/- 252 IU/L, n = 50), p < 0.01. Thirty-two patients had radiographic evaluation for evidence of rickets, based on P-APA greater than 800 IU/L, parenteral nutrition greater than 3 to 4 weeks, or clinical suspicion. Of these, 18 showed radiologic rickets and 14 showed osteopenia without rickets. Infants with BW <600 g were more likely to have radiologic rickets (10/20 infants) compared to those with BW 600–800 g (6/43 infants) and BW 800–1000 g (2/50 infants), p < 0.01 for each. P-APA was not significantly higher in infants with radiologic rickets (1078 +/- 356 IU/L) compared to those without radiologic evidence of rickets (943 +/- 346, p = 0.18). Elevation of P-APA >600 IU/L was very common in ELBW infants. BW was significantly inversely related to both P-APA and radiologic rickets. No single value of P-APA was related to radiological findings of rickets. Given the very high risk of osteopenia and rickets among ELBW infants, we recommend consideration of early screening and early mineral supplementation, especially among infants <600 g BW.