Usefulness of receptor binding domain protein-based serodiagnosis of COVID-19

Abstract

Objectives: This study evaluated the performance of recombinant receptor binding domain (RBD) protein-based enzyme-linked immunosorbent assays (RBD-ELISAs) for detecting anti-SARS-CoV-2 immunoglobulin (Ig) G and IgM antibodies.

Methods: In this study, 705 sera from SARS-CoV-2-infected individuals and 315 sera from healthy individuals were analyzed.

Results: The RBD-ELISA IgG exhibited high specificity (99.1%) and moderate sensitivity (48.0%), with an overall diagnostic accuracy of 73.5%. RBD-ELISA IgM demonstrated specificity at 94.6% and sensitivity at 51.1%, with an accuracy of 72.8%. Both assays displayed improved performance when analyzing samples collected 15-21 days post-symptom onset, achieving sensitivity and accuracy exceeding 88% and 90%, respectively. Combining RBD-ELISA IgG and IgM in parallel analysis enhanced sensitivity to 98.6% and accuracy to 96.2%. Comparing these RBD-ELISAs with commercially available tests, the study found overlapping sensitivity and similar specificity values. Notably, the combined RBD-ELISA IgG and IgM showed superior performance. Cross-reactivity analysis revealed low false-positive rates (4.4% for IgG, 3.7% for IgM), primarily with viral infections.

Conclusion: This research underscores the potential of RBD-based ELISAs for COVID-19 diagnosis, especially when assessing samples collected 15-21 days post-symptom onset and utilizing a parallel testing approach. The RBD protein's immunogenicity and specificity make it a valuable tool for serodiagnosis, offering an alternative to polymerase chain reaction-based methods, particularly in resource-limited settings.

Keywords: Antibody detection; Diagnostic performance; Recombinant RBD protein; SARS-CoV-2; Serodiagnosis.

Figure 1

Flowchart illustrating study design in conformity with the Standards for Reporting of Diagnostic Accuracy Studies (STARD) guidelines.

Figure 2

RI and diagnostic performance metrics for SARS-CoV-2-positive (Pos) and SARS-CoV-2-negative (Neg) serum samples (Panel a) and SARS-CoV-2-positive samples categorized by symptom onset (Panel b). The established RI cut-off value was 1.0 (dashed line), with shaded areas denoting gray zones (RI = 1.0 ± 0.10). Geometric mean RI values and corresponding 95% CI values are represented by solid lines.

Figure 3

Cross-reactivity analysis of the RBD protein with sera from various infectious and parasitic diseases. The cutoff value is set at an RI of 1.0, with the shaded region representing the gray zone (RI = 1.0 ± 0.10).