Table 1.
Test systems assessing anti-SARS-CoV-2 antibodies used in the study.
| Test No. | Test System (Manufacturer) |
Type of Test |
Antibody Isotype | Target Protein |
Positive Result | Grey Zone |
|---|---|---|---|---|---|---|
| 1 * | DS IFA-ANTI-SARS-CoV-2 (NPO “Diagnostic Systems”, Russia) |
Qualitative, ELISA |
IgG + IgM | N and S | COI > Cut-off +20% | Yes (COI between Cut-off −20% to Cut-off +20%) |
| 2 | SARS-CoV-2-IgG-IFA (National Research Center for Hematology, Moscow, Russia) |
Qualitative, ELISA |
IgG | S-RBD | COI ≥ 1.1 | Yes (COI from 0.9 to 1.1) |
| 3 | SARS-CoV-2-IgG-IFA-BEST (Vector-Best, Novosibirsk, Russia) |
Qualitative, ELISA |
IgG | S | COI ≥ 1.1 | Yes (COI from 0.8 to 1.1) |
| 4 | SARS-CoV-2-IgM-IFA-BEST (Vector-Best, Novosibirsk, Russia) |
Qualitative, ELISA |
IgM | N and S-RBD |
COI ≥ 1.1 | Yes (COI from 0.8 to 1.1) |
| 5 | Elecsys Anti-SARS-CoV-2 (Roche Diagnostics, Basel, Switzerland) |
Qualitative, CLIA |
Total Abs | N | COI ≥ 1.0 | No |
| 6 | Elecsys Anti-SARS-CoV-2 S (Roche Diagnostics, Basel, Switzerland) |
Quantitative, CLIA |
Total Abs | S-RBD | U/mL > 0.8 | No |
| 7 | Mindray CLIA IgM (Shenzen Mindray Bio-Medical Electronics Co, Ltd. China) |
Qualitative, CLIA |
IgM | N and S | COI ≥ 1 | No |
* Test DS IFA-ANTI-SARS-CoV-2 specificity was assessed separately for versions 1, 2 and 4/5. ELISA, Enzyme-Linked Immunosorbent Assay. CLIA, Chemiluminescent immunoassay. N, nucleocapsid protein. S, spike protein. RBD, receptor binding domain. COI, cut-off index. The kits used for routine antibody screening in the study tasks 2.1, 2.2 and 2.3 (Figure 1) are highlighted in color.