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Introduction: Dried blood spot (DBS) sampling is a minimally invasive method for specimen collection with potential multifaceted uses, particularly for serosurveillance of previous SARS-CoV-2 infection. In this study, we assessed DBS as a potential specimen type for assessing IgG and total (including IgG and IgM) antibodies to SARS-CoV-2 in vaccinated and naturally infected patients., Methods: Six candidate buffers were assessed for eluting blood from DBS cards. The study utilized one hundred and five paired plasma specimens and DBS specimens from prospectively collected SARS-CoV-2 vaccinated individuals, remnants from those with PCR confirmed SARS-CoV-2 infections, or remnants from those without history of infection or vaccination. All specimens were tested with the Siemens SARS-CoV-2 total assay (COV2T) or IgG assay (sCOVG)., Results: The lowest backgrounds were observed with water and PBS, and water was used for elution. Relative to plasma samples, DBS samples had a positive percent agreement (PPA) of 94.4% (95% CI: 94.9-100%) for COV2T and 79.2 (68.4-87.0) for sCOVG using the manufacturer's cutoff. The NPA was 100 % (87.1-100.0 and 85.13-100) for both assays. Dilution studies revealed 100% (95% CI: 90.8-100%) qualitative agreement between specimen types on the COV2T assay and 98.0% (88.0-99.9%) with the sCOVG using study defined cutoffs., Conclusion: DBS specimens demonstrated high PPA and NPA relative to plasma for SARS-CoV-2 serological testing. Our data support feasibility of DBS sampling for SARS-CoV-2 serological testing., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2021. Published by Elsevier Inc.)

Background: Current serological methods for SARS-CoV-2 lack adequate standardization to a universal standard reference material. Standardization will allow comparison of results across various lab-developed and commercial assays and publications. SARS-CoV-2 EURM-017 is human sera reference material containing antibodies directed against SARS-CoV-2 proteins, S1/S2 (full-length spike [S]), S1 receptor-binding domain (S1 RBD), S1, S2, and nucleocapsid (N) protein. The goal of this study was to characterize five antigen-specific serum fractions in EURM-017 for standardization of serology assays., Methods: Five antigen-specific serum fractions were affinity purified, quantified, and PRNT 50 titers compared. Standardization methods were established for two anti-S1 RBD (IgG and Total Ig) and one N protein assay. For the anti-S1 RBD assays, standardization involved determining assay index values for serial dilutions of S1-RBD anti-sera. Index values for the anti-S1 RBD IgG assay and PRNT 50 titers were determined for 44 symptomatic COVID-19 patient sera. The index values were converted to EURM-017 ug/mL., Results: Anti-sera protein content was as follows: S1 (17.7 µg/mL), S1 RBD (17.4 µg/mL), S1/S2 (full-length S) (34.1 µg/mL), S2 (29.7 µg/mL), and N protein (72.5 µg/mL). S1 anti-serum had the highest neutralization activity. A standardization method for S1 RBD anti-serum and an anti-S1 RBD IgG assay yielded the linear equation (y = 0.75x-0.10; y = index, x=µg/mL anti-serum). Patient sample index values for the S1-RBD IgG assay correlated well with PRNT 50 titers (Pearson r = 0.84). Using the equation above, patient index values were converted to standardized µg/mL., Conclusions: Standardization of different lab-developed and commercial assays to EURM-017 antigen-specific anti-sera will allow comparison of results across studies globally due to traceability to a single standard reference material., (Copyright © 2021 The Canadian Society of Clinical Chemists. Published by Elsevier Inc. All rights reserved.)

Objectives: The ability of current immunoassays to accurately measure equimolar amounts of 25(OH)D2 and 25(OH)D3 has been recently questioned. This study determined serum 25(OH)D2, 25(OH)D3 and total serum 25(OH)D concentrations in healthy vitamin D2-supplemented subjects by isotope dilution liquid chromatography mass spectrometry (ID-LC-MS/MS); and, evaluated the ability of the Siemens, DiaSorin, Roche, and Abbott Vitamin D Total assays to monitor total serum 25(OH)D concentrations compared to an ID-LC-MS/MS method traceable to the National Institute of Standards and Technology (NIST), and that has achieved certification from the Centers for Disease Control and Prevention (CDC) Vitamin D Standardization Certification Program (VDSCP)., Design and Methods: Twenty (20) healthy adults, with no history of prior vitamin D supplementation were administered oral vitamin D2 (2400IU/day for 6months). Serum samples (140) from baseline and monthly blood draws were tested., Results: After one month, the mean serum 25(OH)D2 concentrations rose from 0.8 to 43.6nmol/L, whereas 25(OH)D3 concentrations declined from 84.0 to 63.4nmol/L; total serum 25(OH)D concentrations rose from 86.6 to 107.0nmol/L. The overall mean bias to ID-LC-MS/MS was -7.1% for the Siemens ADVIA Centaur assay, -15.3% for the DiaSorin LIAISON assay; -8.4% for the Roche ELECSYS assay and -16.3% for the Abbott ARCHITECT assay. Correlation coefficients (r) were 0.94, 0.79, 0.74, and 0.73; the mean bias for baseline [25(OH) D3-containing] versus six-month [25(OH)D2- and 25(OH)D3-containing] samples was -13.4% and -5.7%; -3.5% and 20.3%, 9.6% and -12.1%, and 0.2% and -17.8%, respectively., Conclusions: The bias results obtained for the Siemens ADVIA Centaur assay and Roche ELECSYS assay were slightly lower than those for the DiaSorin LIAISON assay and the Abbott ARCHITECT assay, but all 25(OH)D assays demonstrated acceptable performance., (Copyright © 2015 The Canadian Society of Clinical Chemists. Published by Elsevier Inc. All rights reserved.)