Bone Abstracts

Background and Objective: Serum 25-Vitamin D level (S-VitD) was recently reported to be significantly lower in African American (AA) adults compared with their Caucasian (CS) counterparts, despite having a higher bone mineral density, due to lower serum vitamin D-binding protein (NEJM 2013; 369: 1991). The objective of this study was to examine if this observation holds true in Hispanic and AA children.

Material and methods: The database of clinical laboratory from a tertiary level children’s hospital was analyzed from January 2012 to December 2013 for S-VitD, S-PTH and serum creatinine (S-Cr). The data was included for analysis only if all the measurements were done on the same blood sample. Only the initial sample on a given child was included in the analysis. S-VitD was measured by tandem mass spectrometry on AB4000 QTrap with RR of >30–100 ng/ml. S-PTH was measured by an immunoassay (Immulite^TM) with RR of 7–75 pg/ml. S-Cr was measured by an enzymatic assay on Vitros autoanalyzer. The reference range is age based but a cut-off value of <0.6 mg/dl will be normal across the whole pediatric age group. We included S-VitD for children with S-Cr <0.6 mg/dl and S-PTH <250 pg/ml to exclude children with primary hyperparathyroidism, pseudohypoparathyroidism and chronic kidney disease. The SPSS 20 was used for statistical analysis.

Results: The database identified 596 samples (CS=493, AA=54, Hispanic=49) with S-Cr <0.6 mg/dl and S-PTH <250 pg/ml. The mean+S.D. for S-VitD and S-PTH were 35.8±13.7 ng/ml and 38.7±30.4 pg/ml respectively. On univariate analysis S-VitD in AA 30.7±13.5 ng/ml was lower vs CS 37.0±13.5 (P=0.001), and P=NS vs Hispanic children 33.8±14.5, with no difference between CS and Hispanics. There was no statistical difference for S-PTH and S-Cr between the three groups. The boxplot distribution for S-VitD by race is shown in Figure 1. The analysis for children with S-Cr <1.0 mg/dl (n=839) yielded similar results (data not shown).

Conclusions: AA children have significantly lower S-VitD levels compared to CS children with similar S-PTH levels. A comprehensive prospective analysis is needed to validate these findings and develop a robust assay for bioavailable S-VitD in children across different ethnicities.

Disclosure: The authors declared no competing interests.

Figure 1