Prevalence of Vitamin D Deficiency With Biochemical Abnormalities in Children Undergoing Vitamin D Testing

Vitamin D deficiency (VDD) in children can cause hypocalcaemia and rickets, but the prevalence of these complications and the 25-hydroxyvitamin D (25OHD) concentrations below which they arise is uncertain. We investigated this in children (< 18 years) with 25OHD measurements. We obtained 25OHD results from the regional laboratory database, alongside albumin-adjusted serum calcium (aCa), parathyroid hormone (PTH) and alkaline phosphatase (ALP) within 6 months of the index 25OHD. We defined confirmed VDD with biochemical abnormalities (VDDba) as all of low aCa, elevated PTH and elevated ALP. Possible/potential VDDba were defined as 2/3 VDDba criteria with the third test missing (possible), or in the normal range (potential). Clinical records of identified cases were reviewed, and a consensus diagnosis was reached. A total of 30,663 25OHD measurements were identified over 11.5 years (1 January 2009 to 15 June 2020); mean age 8 y, 47% female. After excluding ineligible results, 12,858 25OHD measurements from 9516 individuals with ≥ 2 aCa, PTH and ALP were analysed. Median 25OHD was 61 nmol/L; 36% < 50 nmol/L, 10% < 25 nmol/L. In total, 152 index 25OHD measurements were categorised as VDDba (30 confirmed, 23 possible and 99 potential). Following record review, 118 individuals (111 < 3 years) had 120 clinically confirmed VDDba episodes (62 clinical rickets, 15 biochemical rickets, 16 hypocalcaemia, 23 secondary hyperparathyroidism and 4 partially treated rickets). Fifty-six had undetectable 25OHD, and 104 < 25 nmol/L. The proportion of clinically confirmed VDDba was 0.9% for all eligible 25OHD measurements, and 8% for 25OHD < 25 nmol/L. VDDba is uncommon in children undergoing 25OHD testing, and occurs almost entirely in children < 3 years.