Drying blood spots to monitor SARS-CoV-2 antibodies at home

Due to the rapid human-to-human transmission and predominance of asymptomatic carriers, the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) remains an international health threat despite the introduction of many interventions to slow its spread.

Many countries set up physical separation protocols or lockdown limitations at the beginning of the coronavirus 2019 (COVID-19) the pandemic. At the same time the rapid development of diagnostic assays was conducted and emergency authorization (EUA) was granted by the United States Food and Drug Administration to identify people with active SARS/CoV-2 infections.

Study: Monitoring of SARS-CoV-2 Antibodies Utilizing Dried Blood Spots for Home Collection. Image Credit: worawot300/


While social distancing, diagnostic testing and other measures are vital to stop the spread of SARS-CoV-2, COVID-19 vaccines offer an easier and more reliable method to stop the transmission of viruses. Vaccines are made to stimulate the body’s immune system, which produces antibodies that neutralize the virus. This reduces the intensity and spread of the virus.

Numerous labs and researchers have investigated the use of dried blood spot (DBS) collection to aid in the qualitative and quantitative detection of antibodies to SARS-CoV-2 from the beginning of the outbreak. When you compare DBS results with serum or plasma in proof-of-concept tests, these tests showed good specificity and sensitivity. However more research, including studies that are based on the advice of regulatory agencies is needed before DBS samples are used for at-home self-collection.

The results of the current study, published on the preprint server medRxiv*,constitute a more thorough examination of this assay as contrasted to previous studies with a simplified extraction technique as well as a lower reporting limit for DBS samples and evidence of self-clustering in the sample.

About the study

CLSI EP17 A2 advice was used for assessing the capabilities of detection in the test using DBS extracts. Over the course of four days two different reagent batches were used to create six assays that were blank on 96 fabricated blood samples.

These outcomes had Z-scores higher than 4.7 in comparison to the rest of the results. They were therefore excluded from data analysis. The limit of blank (LOB) for DBS extracts, was calculated using the standard deviation and the mean of the remaining blank results as well as a normal distribution multiplier.

The limit of quantitation (LOQ) of DBS extracts was determined by using 14 fabricated blood samples that covered a concentration range of 0.0528 and 0.648 U/mL. The samples were taken over a period of five days and then tested in triplicate using two different reagents using one instrument. Based on FDA guidelines, the target total variance (CV), and bias for this study was set at 25.0 percent. This is based upon FDA guidelines for ligand binding tests at the lower limit.

After data collection, the imprecision profiles were analysed in EP Evaluator(r), using the Limit of Quantitation module. These results showed that the first reagent batch had a LQ of 0.0873 U/mL, whereas the second reagent lot had a LQ of 0.0736 U/mL.

Acceptable biases also were observed at levels higher than the DBS limit for detection (LOD). Because both imprecision and bias results suggest a LOQ lower than the observed LOD, the LOQ for DBS extracts is in fact equal to the LOD of 0.180 U/mL.

In eight donors, self-collected DBS samples were used in conjunction with serial measurement of SARS-CoV-2 antibody levels after vaccination. Donors collected DBS samples on a regular basis starting before immunization until 19 weeks after the initial vaccination.

The Pfizer-BioNTech COVID-19 vaccination was given to all donors with the second dose administered within three weeks of the first. For samples taken within the first nine days following the first vaccination all donors reported negative DBS findings. Between the days 10 and 16 the antibody levels of each donor exceeded the DBS limit of 0.185 U/mL.

After the second dose of vaccination, the levels of antibodies were elevated rapidly. Many donors overcame the 250 U/mL DBS reporting limit. This is calculated to be around 3,570 U/mL serum. Seven donors had significantly lower levels of antibodies. This is most likely due to the immunosuppressive medication that the donor was taking for a chronic condition.


The comprehensive results of this study prove that using DBS samples to test for SARS-CoV-2 antibodies is a valid method. While DBS samples are dilute during the extraction process the method does have advantages. Sample-to-sample matrix effects were decreased and a lower report LOQ of 0.180 U/mL for DBS samples was achieved when Roche’s Universal Diluent was used as the buffer for extraction.

The dilution of the sample also allowed for a wider range of measurement. A DBS sample with a maximum value of 250 U/mL will have more value than 3,500 U/L blood. These findings, together with a strong correlation to blood serum levels enabled the assay to be utilized to demonstrate antibody tracking over time using DBS self-collection at home.

When the levels of antibodies that indicate protection are more clearly known, DBS samples may become an essential tool for frequent monitoring of antibody levels and scheduling of vaccination boosters.

*Important notice

medRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.

Journal reference:

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Gemma Wilson

Gemma is a journalism graduate with keen interest in covering business news – specifically startups. She has as a keen eye for technologies and has predicted quite a few successful startups over the last couple of years.

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