Qualitative and quantitative detection of SARS-CoV-2 antibodies from dried blood spots

Abstract

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.

High pre‐Delta and early‐Omicron SARS‐CoV‐2 seroprevalence detected in dried blood samples from Kinshasa (D.R. Congo)

“…They have already been used in large‐scale community settings, from serological and molecular testing to antenatal screening. Although DBS eluate performance for SARS‐CoV‐2 antibody testing has been demonstrated to be equivalent to that of serum, 34–39,64 to our knowledge manufacturers have not yet validated DBS as a viable sample. A common observation in real‐world testing scenarios shows that spot quality depends on sample volume and storage conditions, and slight variations in any of them can result in lower‐than‐expected analytic capacity 42,66 .…”

“…When conducting serosurveys in low‐resource settings, dried blood spots (DBS) are a well‐established alternative sample to the traditional serum or plasma sample as they require minimal equipment and training, and samples are easily stored and transported. DBS have proven useful for the serological study of different viral infections (HIV, HCV, HBV) in these regions 32,33 and since the start of the pandemic researchers have confirmed DBS are comparable to serum samples 34–38 and present good performance on various commercial platforms 36,39 . Still, the available commercial assays do not include DBS as an approved sample type and there is limited real‐world comparative performance evidence 40,41 …”

Dried blood spot eluates are suitable for testing of SARS-CoV-2 IgG antibodies targeting Spike protein 1 and Nucleocapsid protein

“…In 2020, initial studies investigated the use of DBS for self-sampling in the context of SARS-CoV-2 antibody testing for selected population groups [ 8 , 9 ]. In-house methods and commercial assays for measurement of SARS-CoV-2 antibodies from DBS emerged [ [10] , [11] , [12] , [13] , [14] ]. In addition to a proof of the principle of antibody testing using DBS, the influence of various parameters, e.g.…”

Detection of SARS-CoV-2 antibodies in serum and dried blood spot samples of vaccinated individuals using a sensitive homogeneous proximity extension assay

“…The Siemens (Munich, Germany) SARS-CoV-2 total antibody assay achieved a 100% and 94% agreement between results for plasma and DBS samples for negative and positive patient samples, respectively. The assay used 6 mm punches from the DBS [10] . A concordance of 98.4% was shown between DBS and venous plasma samples using DBS sample volumes of 150 µl blood by the Architect SARS-CoV-2 IgG assay [11] .…”