Using dried blood drops to monitor SARS-CoV-2 antibodies at home

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

Many countries have established physical separation protocols and / or lockdown limitations early in the 2019 coronavirus disease (COVID-19) pandemic. At the same time, diagnostic tests were rapidly developed and received Emergency Use Clearance (EUA) from the United States Food and Drug Administration (FDA) to identify people with active SARS-CoV infections. -2.

To study: Monitoring for SARS-CoV-2 antibodies using a dried blood spot for home collection. Image Credit: worawot300 / Shutterstock.com

Background

Although social distancing and diagnostic testing remain essential to reduce the spread of SARS-CoV-2, the introduction of COVID-19 vaccinations offers a more reliable approach to restrict viral transmission. Vaccines work by inducing the body’s natural immune response, which results in the production of antibodies that can neutralize the virus, thereby reducing the severity of infections and the transmission of the virus.

Many laboratories and researchers have examined the use of the collection of dried blood drops (DBS) for the qualitative and quantitative detection of anti-SARS-CoV-2 antibodies since the start of the epidemic. When comparing DBS results to plasma or serum in proof-of-concept tests, these tests showed good sensitivity and specificity. However, more research, including studies based on regulatory advice, is needed before DBS samples can be used for home self-collection.

The results presented in this study, which are published on the preprint server medRxiv*, provide a more in-depth review of this assay compared to previous studies, with a simplified extraction technique, a lower reporting limit for DBS samples, and evidence of sample self-aggregation.

About the study

CLSI Advisory EP17-A2 was used to assess the detection capabilities of the assay with DBS extracts. Over the course of four days, two different reagent lots were used to produce 96 blank tests on six fabricated blood samples.

The z-score for each of these results, relative to the other results, was greater than 4.7 for both reagent lots; they were therefore excluded from the data analysis. The blank limit (LOB) for the DBS extracts was calculated using the mean and standard deviation of the remaining blank results, as well as a normal distribution multiplier.

The limit of quantification (LOQ) of the DBS extracts was determined using 14 fabricated blood samples covering an appropriate concentration range between 0.0528 and 0.648 U / mL. Over a five day period, these samples were extracted and measured in triplicate using two different reagent lots on a single instrument. The target total variance (CV) and bias for this study was set at 25.0%, which is based on the FDA guidelines for lower limit of quantification ligand binding assays.

After data collection, imprecision profiles were analyzed in EP Evaluator® using the Limit of Quantitation module. These results showed that the first lot of reagents had an LOQ of 0.0873 U / mL, while the second lot of reagents had an LOQ of 0.0736 U / mL.

In addition, for all levels above the limit of detection (LOD) of DBS, acceptable biases of less than 25.0% were observed. Since the imprecision and bias results indicate an LOQ less than the observed LOD, the LOQ for the DBS extracts is effectively equal to the LOD of 0.180 U / mL.

In eight donors, self-collected DBS samples were used in conjunction with serial measurements of SARS-CoV-2 antibody levels after vaccination. Donors routinely collected samples of DBS prior to vaccination up to 19 weeks after the first vaccination.

The Pfizer-BioNTech COVID-19 vaccine was administered to all donors, with the second dose being given exactly three weeks after the first. For samples collected within the first nine days of the first immunization, all donors reported negative DBS results. Between 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, antibody levels increased rapidly, with several donors exceeding the DBS reporting limit of 250 U / mL, which is calculated at 3,570 U / mL in serum. Donor seven had significantly lower antibody levels, which were most likely caused by the immunosuppressive drug the donor reported taking for a chronic illness.

Implications

The comprehensive results presented in this study show that using DBS samples to measure SARS-CoV-2 antibodies is a reliable method. Although the DBS samples are diluted during the extraction procedure, this method has advantages. Sample-to-sample matrix effects were reduced and a lower LOQ ratio of 0.180 U / mL for DBS samples was obtained when Roche’s Universal Diluent was used as the extraction buffer.

Additionally, sample dilution allowed for a wider relative measuring range, as a DBS sample with a maximum concentration of 250 U / mL would be greater than 3,500 U / L in blood. These results, along with a strong correlation with venous serum data, allowed the assay to be used to demonstrate antibody tracking over time using DBS self-collection at home.

When the levels of antibodies inferring protective immunity are better understood, DBS samples can become an essential tool for frequent monitoring of antibodies and scheduling boosters.

*Important Notice

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

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