Exogenous versus endogenous recovery of 25-hydroxyvitamins D 2 and D 3 in human samples using high-performance liquid chromatography and the DiaSorin LIAISON Total-D Assay

Abstract

Demand for circulating 25-hydroxyvitamin D [25(OH)D] measurements has exploded due to its relationship with many serious health problems. The present study was designed to investigate the validity of samples “spiked” with 25-hydroxyvitamin D 2 [25(OH)D 2] or 25-hydroxyvitamin D 3 [25(OH)D 3] to determine their analytical recovery by the DiaSorin LIAISON 25 OH Vitamin D Total Assay (DiaSorin Assay) and high-performance liquid chromatography (HPLC). 25(OH)D was measured in nine volunteers taking large daily doses of vitamin D 2 for 2 weeks. Samples were obtained pre-supplementation and 1 week following vitamin D 2. Pre-supplementation samples were used for exogenous recovery studies by adding 25(OH)D 2 or 25(OH)D 3. Endogenous 25(OH)D [25(OH)D 2 plus 25(OH)D 3] concentrations reported by the DiaSorin Assay or detected by HPLC were in excellent agreement. However, exogenously added 25(OH)D 2 and 25(OH)D 3 were under-recovered by the DiaSorin Assay. NIST vitamin D standards containing serum from another species (horse) or exogenous 25(OH)D 2 were similarly affected when using the DiaSorin Assay. Exogenous 25(OH)D 2, 25(OH)D 3 or serum from other species added to human samples is inappropriate in determining the analytical recovery of vitamin D compounds when using the DiaSorin Assay. Only endogenous 25(OH)D 2 and/or 25(OH)D 3 contained in human blood samples should be utilized for this purpose.