Assessment of vitamin D status using MitraTM volumetric absorptive microsampling (VAMS) device

Jonathan C Y Tang (Lead Author), Holly Nicholls, Nicole Ball, John Dutton, Isabelle Piec, James Rudge, Christopher Washbourne, William Fraser

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Introduction: The use of dried blood spot (DBS) sampling for general wellness assessment and in clinical diagnostics has gained popularity as a convenient and less invasive alternative to venous sampling. Collection of blood samples from a finger/heel prick using conventional filter paper suffers from variability in sample volume and spot sizes which undermine the quality of results. We describe the use of a volumetric absorptive microsampler (VAMS), called MitraTM (Torrance, CA, USA) for measurement of 25OHD3 and interpretation of vitamin D status according to current international guidelines. 
Method: A liquid-chromatography mass spectrometry (LC-MS/MS) method was used for measurement of 25OHD3 (Tang et al. ASBMR 2015, LB-MO0026). We compared results from patient samples (n=97) collected by VAMS and Whatman® 903 cards extracted as whole spot (wDBS) and sub-punches (spDBS) against plasma 25OHD3 concentration. We investigated the volume displacement effects of haematocrit (Hct) on DBS 25OHD3 measurements and described the use of DBS-to-plasma equivalence value (PEV) to allow accurate interpretation of vitamin D status. 
Results: VAMS showed the best assay precision CV (<8.2%) compared to wDBS (<16.6%) and spDBS (<15.1%) across the assay range of 0.1-125 nmol/L, the least variability in recovery and lowest LLoQ (Figure 1). We observed a decrease in DBS 25OHD3 concentration in proportion to the reduction in plasma volume and increase in packed cell volume. The displacement effect of Hct resulted in a strong but negatively biased correlation (r2=0.893, -39.3%) between raw DBS values and plasma concentrations, that was dependent upon the level of Hct present in sample. We demonstrated the use of simple linear regression model to transform raw DBS values into PEVs. In a subsequent cohort of patient samples (n=70), PEVVAMS produced the most accurate interpretation of vitamin D status compared to PEVwDBS and PEVspDBS. 
Discussion: We present data supporting the use of VAMS for measurement of 25(OH)D3, particularly in circumstances where venesection may be impossible or difficult and where sample volume may be limited. Although the recovery of analyte remains Hct-dependent, the use of DBS-to-plasma equivalence values improves the clinical applicability and broadens the utility of DBS as a sampling technique.
Original languageEnglish
Publication statusPublished - 9 Sep 2017
EventASBMR 2017 Annual Meeting - Colorado Convention Center, ASBMR Discovery Hall, United States
Duration: 8 Sep 201711 Sep 2017


ConferenceASBMR 2017 Annual Meeting
Country/TerritoryUnited States

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