Total 25-Hydroxyvitamin D Measurement May Not be a Sensitive Screening Method to Detect Vitamin D Deficiency in Some Ethnic Pediatric Populations

Presentation Number: SUN 355
Date of Presentation: April 2nd, 2017

Elwaseila Hamdoun*1, Thereza Piloya2, Sarah E Cusick1, Brandon M Nathan1, Zahra Mahamed1, Antoinette Moran1, Anna Petryk1 and Muna Sunni1
1University of Minnesota, Minneapolis, MN, 2University of Makerere Mulago Hospital, Kampala, Uganda

Abstract

BACKGROUND

Total 25-dihydroxyvitamin D (T25OHD) is frequently low in African Americans who exhibit no clinical or biochemical manifestation of deficiency, though it is universally accepted as a sensitive screening tool. New evidence cast doubts on its usefulness in detecting true cases of vitamin D deficiency in some African children.

METHODS

We measured T25OHD and other vitamin D metabolites by mass spectrometry, parathyroid hormone [PTH] by immunoassay, and serum albumin and calcium by bichromatic end point method in 3 groups of well children age ≤7: white Caucasian Minnesotans (n=14), Minnesotans of Somali descent (n=55), and Ugandans in Africa (n=99, equatorial latitude).

RESULTS

Vitamin D levels <30 ng/ml were found in 64% of Caucasians, 91% of Somalis and 49% of Ugandans. Of those, 89% of Caucasians, 52% of Somalis and 12% of Ugandans were hypocalcemic (corrected total serum Ca<9.1 mg/dl for age≥11 months, and 8.5 for age<11 months). For vitamin D levels <20 ng/ml, 100% of Caucasians, 38% of Somalis and 0% of Ugandans were hypocalcemic. PTH and ALK means (SD) for the groups are 35.75 (18), 302.48 (119.04) for Caucasians, 44.64 (21.12), 287 (110.93) for Somalis, and 47.48 (18.91), 262.81 (62.57) for Ugandans, respectively. Across all groups, higher PTH was associated with hypocalcemia (r= -0.32, P = <0.0001) but not with T25OHD status (D<30, r= -0.07, p=0.6). Assuming hypocalcemia represents true vitamin D deficiency status, T25OHD<30 ng/ml (ENDO insufficiency guidelines), had an overall sensitivity of 74% (72%, 92%, 40%, for White, Somali, and Ugandan groups respectively. We have found a positive correlation between a promising new biomarker, the ratio of inactivated vitamin D (24,25(OH)2D3) to T25OHD [24/25D ratio], and serum calcium (r=0.35, p=<0.0001).

CONCLUSIONS

Measurement of T25OHD may neither be sufficient to evaluate significance of underlying metabolic derangements related to vitamin D status nor inform clinical decision about therapy in African children. Future work will test participants’ vitamin D binding protein levels, its haplotype, and calculate free and bioavailable 25OHD to better explore the observed correlation of 24/25D ratio with calcium levels and whether it can serve as a better indicator of vitamin D status and mineral metabolism.

 

Nothing to Disclose: EH, TP, SEC, BMN, ZM, AM, AP, MS