Abstract
The SARS-CoV-2 IgG II Quant assay for measuring COVID-19 antibodies has previously been validated to have an analytical sensitivity of 99.35% using venous blood samples. In this study, we correlated the COVID-19 antibody levels measured in capillary blood with the antibody levels measured using venous blood. Additionally, we evaluated the stability of capillary blood measurements at 1, 3 and 10 days after collection and at different temperatures.
We found excellent correlation between the antibody levels measured using capillary blood vs venous blood. The overall correlation coefficient was 0.999. We also found that the antibody levels can be measured with very high accuracy even 10 days after collection (r>0.99) or if the sample is exposed to temperatures up to 32°C (r>0.99). Overall, we found that measuring COVID-19 antibody levels using capillary blood is highly accurate and stable.
Introduction
COVID-19 is caused by severe acute respiratory syndrome coronavirus 2 virus (SARS-CoV-2). The SARS-CoV-2 IgG II Quant assay detects immunoglobulin class G (IgG) antibodies, including neutralizing antibodies, to the receptor binding domain (RBD) of the S1 subunit of the spike protein of SARS-CoV-2. This assay has previously been validated by Abbott laboratories to have an analytical sensitivity of 99.35% using venous blood samples. In this study, we evaluated how well the COVID-19 antibody levels measured in capillary blood correlates with the antibody levels measured using venous blood. Additionally, we evaluated the stability of measurements at 1,3 and 10 days after collection and at different temperatures.
Methods
75 individuals (Aged 21-69, 59% females and 41% males) who provided informed consent were included in this study. Two samples were collected from each individual – A venous blood sample and a capillary blood sample. The SARS-CoV-2 IgG II Quant assay was performed on both these samples using Alinity I system. All the venous blood samples were tested within 24 hours of collection. The capillary blood samples were measured at different time points and at different temperatures as shown in the table below:
Table 1. Table showing the time points and temperatures at which the tests were performed. Room temperature is 22°C.
Table 2. Temperature cycle of samples beginning from when they were collected. 15 samples from Day 3 went through 1 temperature cycle. 15 samples from Day 10 went through 2 temperature cycles before being stored at 4 degrees for 5 days.
Statistical Analysis: For each of the 5 combinations of timepoints and temperatures indicated in Table 1, a correlation coefficient is calculated by comparing the data from capillary blood samples to venous blood samples.
Results
Table 3 below shows the correlation of COVID-19 antibody levels between venous blood and Capillary blood.
Table 3. Table showing the Correlation coefficients of antibody levels at different time points and different temperature settings
Figures 1-5 below show the corresponding scatter plots showing COVID-19 antibody levels between venous blood and Capillary blood.
Figure 1. Scatter plot showing the relationship between the COVID-19 antibody levels from capillary blood vs venous blood when measurements were taken within 24 hours of sample collection at room temperature.
Figure 2. Scatter plot showing the relationship between the COVID-19 antibody levels from capillary blood vs venous blood when measurements were taken at 3 days of sample collection that have gone through temperature cycling indicated in Table 2.
Figure 3. Scatter plot showing the relationship between the COVID-19 antibody levels from capillary blood vs venous blood when measurements were taken at 3 days of sample collection at room temperature.
Figure 4. Scatter plot showing the relationship between the COVID-19 antibody levels from capillary blood vs venous blood when measurements were taken at 10 days of sample collection that have gone through temperature cycling indicated in Table 2.
Figure 5. Scatter plot showing the relationship between the COVID-19 antibody levels from capillary blood vs venous blood when measurements were taken at 10 days of sample collection at room temperature.
Conclusion
Data collected from this study provide strong support that the COVID-19 antibody levels measured using capillary blood correlate excellently (r>0.99). This study also shows that the COVID-19 antibody levels from capillary blood are stable up to 10 days and at high temperature.
