Simpson CA, Zhang JH, Vanderschueren D, et al. - As serum total 25-hydroxyvitamin D (t25-OHD) is assessed to determine vitamin D status, researchers examined if free 25-hydroxyvitamin D measures better correlate with various clinical outcomes in children, across the 6 common GC haplotypes. They performed measurement total and free 25-OHD and 1,25(OH)2D, calcium, phosphate, parathyroid hormone (PTH), glucose, insulin, aldosterone, and renin in 203 healthy, urban-dwelling children, aged 6 months to 10 years, mainly of Hispanic background and representative of all common GC haplotypes. Outcomes suggest that healthy children exhibit circulating total and free 25-OHD as comparable measures of vitamin D status. Similar correlations were observed with other outcome variables, however the strongest correlate of circulating PTH and other variables was t25-OHD. The data thereby do not support routine refinement of the t25-OHD measure using currently available assessments of free 25-OHD.