Publications by authors named "Brett Holmquist"
Article Synopsis
- The Vitamin D External Quality Assessment Scheme (DEQAS) sends human serum samples to over 1000 global participants to measure total serum 25-hydroxyvitamin D levels four times a year.
- A study was conducted to determine if shipping these samples at ambient temperature affects the reliability of various 25(OH)D assays compared to shipping them frozen.
- Results showed significant differences for four specific assays when samples were shipped ambiently, but all 14 LC-MS/MS assays showed no significant differences, indicating they remained stable during shipping at room temperature.
An interlaboratory comparison study was conducted by the Vitamin D Standardization Program (VDSP) to assess the performance of liquid chromatography - tandem mass spectrometry (LC-MS/MS) assays used for the determination of serum total 25-hydroxyvitamin D (25(OH)D), which is the sum of 25-hydroxyvitamin D (25(OH)D) and 25-hydroxyvitamin D (25(OH)D). A set of 50 single-donor samples was assigned target values for concentrations of 25(OH)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 1 includes results from 14 laboratories using 14 custom LC-MS/MS assays.
View Article and Find Full Text PDFArticle Synopsis
- - An interlaboratory study was conducted by the Vitamin D Standardization Program (VDSP) to evaluate how well Standard Reference Materials (SRMs) and proficiency testing samples can be used interchangeably for measuring serum total 25-hydroxyvitamin D levels using different assay methods.
- - A total of 50 single-donor serum samples were tested across 28 laboratories using a mix of 20 ligand binding assays and 14 LC-MS/MS methods, with target values assigned based on reference measurement procedures.
- - Results showed that certain SRM and proficiency testing samples were found to be non-commutable for specific assays, particularly indicating that SRM 972a (with high 3-epi-25(OH)
Ion mobility was integrated with liquid chromatography/high resolution mass spectrometry (LC/IM-HRMS) to quantify 25-hydroxyvitamin D (25OHD) in human serum. It has previously been shown that 25OHD adopts two gas-phase conformations which are resolved using ion mobility; in contrast, the inactive epimer, 3-epi-25-hydroxyvitamin D (epi25OHD), only adopts one. Interference from epi25OHD was eliminated by filtering the chromatogram to retain the drift time that corresponds to the unique gas-phase conformation of 25OHD.
View Article and Find Full Text PDFVitamin D deficiency and depressive symptoms in the perinatal period.
Arch Womens Ment Health
December 2018
Depression affects 1 in 7 women during the perinatal period. Women with vitamin D deficiency may be at an increased risk for depression. This study investigated the relationship between maternal and cord blood 25-hydroxyvitamin D (25OHD) and maternal depressive symptoms over the perinatal period.
View Article and Find Full Text PDFContext: Controversy persists over: 1) how best to restore low serum 25-hydroxyvitamin D (25D) levels (vitamin D2 [D2] vs vitamin D3 [D3]); 2) how best to define vitamin D status (total [protein-bound + free] vs free 25D); and 3) how best to assess the bioactivity of free 25D.
Objective: To assess: 1) the effects of D2 vs D3 on serum total and free 25D; and 2) whether change in intact PTH (iPTH) is more strongly associated with change in total vs free 25D.
Design: Participants previously enrolled in a D2 vs D3 trial were matched for age, body mass index, and race/ethnicity.