• Assessment of serum total 25-hydroxyvitamin D assay commutability of Standard Reference Materials and College of American Pathologists Accuracy-Based Vitamin D (ABVD) Scheme and Vitamin D External Quality Assessment Scheme (DEQAS) materials: Vitamin D Standardization Program (VDSP) Commutability Study 2.

      Camara, Johanna E; Wise, Stephen A; email: stephen.wise@nih.gov; Hoofnagle, Andrew N; Williams, Emma L; Carter, Graham D; Jones, Julia; Burdette, Carolyn Q; Hahm, Grace; Nalin, Federica; Kuszak, Adam J; et al. (2021-06-28)
      An interlaboratory study was conducted through the Vitamin D Standardization Program (VDSP) to assess commutability of Standard Reference Materials® (SRMs) and proficiency testing/external quality assessment (PT/EQA) samples for determination of serum total 25-hydroxyvitamin D [25(OH)D] using ligand binding assays and liquid chromatography-tandem mass spectrometry (LC-MS/MS). A set of 50 single-donor serum samples were assigned target values for 25-hydroxyvitamin D [25(OH)D ] and 25-hydroxyvitamin D [25(OH)D ] using reference measurement procedures (RMPs). SRM and PT/EQA samples evaluated included SRM 972a (four levels), SRM 2973, six College of American Pathologists (CAP) Accuracy-Based Vitamin D (ABVD) samples, and nine Vitamin D External Quality Assessment Scheme (DEQAS) samples. Results were received from 28 different laboratories using 20 ligand binding assays and 14 LC-MS/MS methods. Using the test assay results for total serum 25(OH)D (i.e., the sum of 25(OH)D and 25(OH)D ) determined for the single-donor samples and the RMP target values, the linear regression and 95% prediction intervals (PIs) were calculated. Using a subset of 42 samples that had concentrations of 25(OH)D below 30 nmol/L, one or more of the SRM and PT/EQA samples with high concentrations of 25(OH)D were deemed non-commutable using 5 of 11 unique ligand binding assays. SRM 972a (level 4), which has high exogenous concentration of 3-epi-25(OH)D , was deemed non-commutable for 50% of the LC-MS/MS assays.
    • Interlaboratory comparison of 25-hydroxyvitamin D assays: Vitamin D Standardization Program (VDSP) Intercomparison Study 2 - Part 2 ligand binding assays - impact of 25-hydroxyvitamin D

      Wise, Stephen A; email: stephen.wise@nih.gov; Camara, Johanna E; Burdette, Carolyn Q; Hahm, Grace; Nalin, Federica; Kuszak, Adam J; Merkel, Joyce; Durazo-Arvizu, Ramón A; Williams, Emma L; Popp, Christian; et al. (2021-08-25)
      An interlaboratory comparison study was conducted by the Vitamin D Standardization Program (VDSP) to assess the performance of ligand binding assays (Part 2) for the determination of serum total 25-hydroxyvitamin D [25(OH)D]. Fifty single-donor samples were assigned target values for concentrations of 25-hydroxyvitamin D [25(OH)D ], 25-hydroxyvitamin D [25(OH)D ], 3-epi-25-hydroxyvitamin D [3-epi-25(OH)D ], and 24R,25-dihydroxyvitamin D [24R,25(OH) D ] using isotope dilution liquid chromatography-tandem mass spectrometry (ID LC-MS/MS). VDSP Intercomparison Study 2 Part 2 includes results from 17 laboratories using 32 ligand binding assays. Assay performance was evaluated using mean % bias compared to the assigned target values and using linear regression analysis of the test assay mean results and the target values. Only 50% of the ligand binding assays achieved the VDSP criterion of mean % bias ≤ |± 5%|. For the 13 unique ligand binding assays evaluated in this study, only 4 assays were consistently within ± 5% mean bias and 4 assays were consistently outside ± 5% mean bias regardless of the laboratory performing the assay. Based on multivariable regression analysis using the concentrations of individual vitamin D metabolites in the 50 single-donor samples, most assays underestimate 25(OH)D and several assays (Abbott, bioMérieux, DiaSorin, IDS-EIA, and IDS-iSYS) may have cross-reactivity from 24R,25(OH) D . The results of this interlaboratory study represent the most comprehensive comparison of 25(OH)D ligand binding assays published to date and is the only study to assess the impact of 24R,25(OH) D content using results from a reference measurement procedure. [Abstract copyright: © 2021. This is a U.S. government work and not under copyright protection in the U.S.; foreign copyright protection may apply.]