Dried blood spot specimens for SARS-CoV-2 antibody testing: A multi-site, multi-assay comparison

The true severity of infection due to COVID-19 is under-represented because it is based on only those who are tested. Although nucleic acid amplifications tests (NAAT) are the gold standard for COVID-19 diagnostic testing, serological assays provide better population-level SARS-CoV-2 prevalence estimates. Implementing large sero-surveys present several logistical challenges within Canada due its unique geography including rural and remote communities. Dried blood spot (DBS) sampling is a practical solution but comparative performance data on SARS-CoV-2 serological tests using DBS is currently lacking. Here we present test performance data from a well-characterized SARS-CoV-2 DBS panel sent to laboratories across Canada representing 10 commercial and 2 in-house developed tests for SARS-CoV-2 antibodies. Three commercial assays identified all positive and negative DBS correctly corresponding to a sensitivity, specificity, positive predictive value, and negative predictive value of 100% (95% CI = 72.2, 100). Two in-house assays also performed equally well. In contrast, several commercial assays could not achieve a sensitivity greater than 40% or a negative predictive value greater than 60%. Our findings represent the foundation for future validation studies on DBS specimens that will play a central role in strengthening Canada’s public health policy in response to COVID-19.

Monitoring of SARS-CoV-2 Antibodies Using Dried Blood Spot for At-Home Collection

The utilization of vaccines to fight the spread of SARS-CoV-2 has led to a growing need for expansive serological testing. To address this, an EUA approved immunoassay for detection of antibodies to SARS-CoV-2 in venous serum samples was investigated for use with dried blood spot (DBS) samples. Results from self-collected DBS samples demonstrated a 98.1% categorical agreement to venous serum with a correlation (R) of 0.9600 while professionally collected DBS samples demonstrated a categorical agreement of 100.0% with a correlation of 0.9888 to venous serum. Additional studies were performed to stress different aspects of at-home DBS collection, including shipping stability, effects of interferences, and other sample-specific robustness studies. These studies demonstrated a categorical agreement of at least 95.0% and a mean bias less than ±20.0%. Furthermore, the ability to track antibody levels following vaccination with the BioNTech/Pfizer vaccine was demonstrated with serial self-collected DBS samples from pre-dose (Day 0) out to 19 weeks.

ANALYSIS OF CYCLOPHOSPHAMIDE-INDUCED N5-NITROGEN MUSTARD FORMAMIDOPYRIMIDINE ADDUCT IN DRIED BLOOD SPOT USING LIQUID CHROMATOGRAPHY-TANDEM MASS SPECTROMETRY

Cyclophosphamide is one of the nitrogen mustard agents that is frequently used in cancer chemotherapy. Nevertheless, long-term use of high dosage cyclophosphamide has been proven to increase the risk of secondary cancer. This can be traced by the mutagenic DNA adduct formation, for instance, N5-nitrogen mustard formamidopyrimidine (NM-Fapy-G). Therefore, it may serve as one of the secondary cancer biomarkers in patients receiving cyclophosphamide. Several NM-Fapy-G analysis methods employ Liquid Chromatography-Tandem Mass Spectrometry (LC-MS/MS) developed by experts. However, it was discovered not applicative for patients because cells and tissues were utilized as the biospecimens. Therefore, this summary is presented to emphasize the idea of adopting Dried Blood Spot (DBS) as the blood bio sampling method, DNA extraction and hydrolysis method that is suitable for enriching NM-Fapy-G adduct; and method that is proper for NM-Fapy-G analysis. Based on the literature study, DBS has been proven beneficial for this analysis; DNA can be extracted from the DBS cards using the QIAamp DNA Mini Kit. Therefore, research with a little bit of adjustment can be applied for NM-Fapy-G analysis.