Evaluation of COVID-19 antibody response with using three different tests

Abstract

Background and Objectives: In this study, the performance of three different commercial antibody assays for COVID-19 was examined and parameters affecting the antibody response were investigated. The correlation of patients’ chest CT results, procalcitonin, CRP, and D-dimer levels with the antibody response were retrospectively evaluated.
 Materials and Methods: COVID-19 antibodies were detected by three commercially available assays in each patient. Two of the assays were rapid immunochromatographic tests and - one was an ELISA-based IgG assay. SARS-CoV-2 RNA was tested by “COVID-19 RT-qPCR Detection Kit” using nasopharyngeal swab samples. The results of antibody tests were com- pared with each other, RT-qPCR, Biochemical parameters and chest CT findings.
 Results: RT-qPCR was positive in 46.6% (41/88) of the evaluated patients among which 77.3% (68/88) were healthcare workers. Seventeen (41.4%) of viral RNA positive patients had a positive antibody result with at least two assays. Both of the rapid immunochromatographic tests had identical sensitivity of 36.6% and specificity of 100%, compared to RT-qPCR assay; while the sensitivity of the ELISA based Euroimmune test was 43.9%, and the specificity was 95.7%. The sensitivity and specificity of the immunochromatographic tests were 75% and 100% respectively, compared to ELISA test result. There was a correlation between antibody positivity and old age and male gender. The presence of typical chest CT findings increased the antibody positivity 13.62 times. Antibody positivity was also increased with the decrease in Ct value of the PCR assay. There was no significant relationship between the biochemical parameters (CRP, D-dimer and procalcitonin values) and the antibody or RT-qPCR results.
 Conclusion: There was a correlation between antibody response and male gender, older age, presence of symptoms, typical chest CT findings and low PCR-Ct value.

Reliability of antibody tests for COVID-19 diagnosis

“…higher than ours but were very close to the values mentioned in the literature[3,9,[12][13][14][15][16][17][18][19][20][21].…”

“…This shows that some patients might have been positive for some antibodies, while others might have been negative. As can be seen in Figures 1 and 2 [3,9,[12][13][14][15][16][17][18][19][20][21]. In one of these studies, the sampling time median was 12 days after symptom onset, which was earlier than ours, and it was mentioned that both the blood sample collection timing and the disease severity could potentially affect the sensitivity of the assays [3].…”

“…Positive sera were obtained from blood samples collected 3-9 weeks after hospital discharge from 98 patients with positive COVID-19 RT-PCR results within the period from March 18 to July 31, 2020. The numbers of sera according to the time of blood sample collection in weeks were 5,20,19,13,26,14, and 1 at 3, 4, 5, 6, 7, 8, and 9 weeks, respectively. All the sera were kept at -20°C until they were studied.…”

Impact of SARS-CoV-2 RNA titer on the level of IgG antibodies in recovered patients with COVID-19 disease

“…Wellinghausen et al [30] explained the lower SARS-CoV-2 IgG in asymptomatic patients by the lower viral load demonstrated by high Ct values. In addition, Appak et al [32] concluded that higher Anti-SARS-CoV-2 antibodies are correlated with lower Ct values. This is in accordance with our results that the level of anti-RBD-spike antibodies correlates positively with presenting symptoms.…”