269 Oral vitamin D2 supplementation in children with cystic fibrosis makes a relatively small contribution to total serum 25OH vitamin D levels

Abstract

Objectives: To assess the relationship between measured vitamin D and parathyroid hormone (PTH) levels in children with CF, and to assess the clinical ability of a low vitamin D level to predict a raised PTH. Methods: 65 paired 25OH vitamin D (25OHD) and PTH levels from children attending for annual review in a single year were analysed. The correlation between 25OHD and PTH was ascertained. Regression analysis was used to assess the relationship between 25OHD and PTH. Comparative statistics were used to assess the differences in PTH level between those children regarded as Vitamin D sufficient, insufficient or deficient. Results: • 25OHD results were normally distributed (mean = 52.4 nmol/l, SD = 23.7). • Only 5 of all PTH results (median 2.95 pmol/l, interquartile range 2.04) were above the upper limit of our laboratory’s quoted reference standard. • Although there was a weak negative correlation between 25OHD and PTH (r = −0.18), a wide range of PTH values (mostly within the laboratory reference range) was observed at all 25OHD levels. • Regression analysis showed no meaningful functional relationship between 25OHD and PTH (R2 = 0.03). • Whilst there was a tendency toward lower PTH values with higher 25OHD levels, this was not statistically significant between the groups of children regarded as Vitamin D sufficient, insufficient or deficient. Conclusions: • Almost all children with CF in our population had PTH levels within the laboratory reference range. • The small numbers of elevated PTH levels were not confined to the vitamin D deficient children. • No reliable inference regarding any likely PTH response to a given 25OHD can be made from a single 25OHD result.