Automated Measurement of Total 25 Vitamin D
on the IDS-iSYS System
Introduction: Most health professionals know vitamin D for its critical role in increasing the efficiency of dietary calcium absorption and preventing rickets in children. In the past decade, emerging research has also uncovered other important relationships between vitamin D and bone health as well as new information indicating it could potentially play a significant role in strengthening the body’s defenses against chronic and autoimmune diseases and in controlling the growth of cells (both normal and cancerous). These new evidences have fuelled the global demand for 25-OH D testing. Clinical laboratories are under pressured to seek automated reliable platforms for 25-OH D analysis to keep up with the demanded volume. Immunodiagnostics System (IDS) has commercialized a direct, fully automated, co-specific immunoassay for 25-OH D for use on the IDS-iSYS system. We seek to assess the analytical performance of the IDS-iSYS 25-OH D assay, and to compare this method to LC-MS/MS, DiaSorin Liaison, and DiaSorin RIA methods. Methods: We determined the repeatability and reproducibility on 6 pools, ranging from 6.2 ng/mL to 71.2 ng/mL, the limit of quantification (LoQ) and the accuracy profile of the IDS-iSYS 25-OH D method. A total of 88 samples, selected to represent a wide range of 25-OH D concentrations [5.6-85.6ng/mL], was assayed by each method.
Results: Intra and inter-assay coefficients of variation (CV) were <11% at 6.2 ng/mL and <8% at 71.25 ng/mL. The LoQ was established at 6.2 ng/mL. The accuracy profile between 6.2 and 71.2ng/mL showed that the risk that one result falls out of the ±30% acceptance limit is <5%, indicating that the method is completely validated in this range. The actual assay working range is 5 to 140ng/mL. A comparison of IDS-iSYS 25-OH D with LC-MS/MS yielded the Passing Bablok fit equation: IDS-iSYS = 1.03 x (LC-MS/MS) + 1.50. The corresponding equation with Liaison was: IDS-iSYS = 0.94 x (Liaison) + 2.41, and with RIA: IDS-iSYS = 1.00 x (RIA) – 0.62.
