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Diagnostic performances and thresholds: The key to harmonization in serological SARS-CoV-2 assays?
Mario Plebani1, Andrea Padoan1, Davide Negrini2
1Department of Laboratory Medicine, University Hospital of Padova, Italy; Department of Medicine-DIMED, University of Padova, Italy.
Insights
Optimized thresholds for SARS-CoV-2 IgG antibody assays improve accuracy and agreement. This helps identify at-risk individuals for monitoring and prevents further viral spread.
Area of Science:
- Immunology
- Infectious Diseases
- Medical Diagnostics
Background:
- Accurate evaluation of SARS-CoV-2 IgG antibody assays is crucial for monitoring virus spread.
- This study compares the reliability of three chemiluminescent (CLIA) and two enzyme-linked immunosorbent (ELISA) assays.
Purpose of the Study:
- To evaluate and compare the performance of different SARS-CoV-2 IgG antibody assays.
- To determine optimal thresholds for CLIA assays to improve diagnostic accuracy and inter-assay agreement.
Main Methods:
- Tested sera from 271 subjects (64 confirmed SARS-CoV-2 patients) using Maglumi, Liaison, iFlash (CLIA), Euroimmun, and Wantai (ELISA) assays.
- Evaluated diagnostic sensitivity, specificity, and likelihood ratios using manufacturer and optimized thresholds.
Main Results:
- Optimized thresholds improved negative likelihood ratios and accuracy for CLIA assays (Maglumi: 93.5%, Liaison: 93.1%, iFlash: 91%).
- CLIA assays showed sensitivities and specificities above 93.8% and 85.9%.
- Overall agreement was high for both CLIA (90.3%) and ELISA (98.4%) assays.
Conclusions:
- Redefined thresholds for CLIA assays enhance the negative likelihood ratio, aiding in identifying at-risk individuals.
- Improved inter-assay agreement facilitates better harmonization of serological test results.
- These findings support closer monitoring of individuals with negative test results to prevent further SARS-CoV-2 transmission.
Background:
The evaluation of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) specific antibody (Ab) assay performances is of the utmost importance in establishing and monitoring virus spread in the community. In this study focusing on IgG antibodies, we compare reliability of three chemiluminescent (CLIA) and two enzyme linked immunosorbent (ELISA) assays.
Methods:
Sera from a total of 271 subjects, including 64 reverse transcription-polymerase chain reaction (RT-PCR) confirmed SARS-CoV-2 patients were tested for specific Ab using Maglumi (Snibe), Liaison (Diasorin), iFlash (Yhlo), Euroimmun (Medizinische Labordiagnostika AG) and Wantai (Wantai Biological Pharmacy) assays. Diagnostic sensitivity and specificity, positive and negative likelihood ratios were evaluated using manufacturers' and optimized thresholds.
Results:
Optimized thresholds (Maglumi 2 kAU/L, Liaison 6.2 kAU/L and iFlash 15.0 kAU/L) allowed us to achieve a negative likelihood ratio and an accuracy of: 0.06 and 93.5% for Maglumi; 0.03 and 93.1% for Liaison; 0.03 and 91% for iFlash. Diagnostic sensitivities and specificities were above 93.8% and 85.9%, respectively for all CLIA assays. Overall agreement was 90.3% (Cohen's kappa = 0.805 and SE = 0.041) for CLIA, and 98.4% (Cohen's kappa = 0.962 and SE = 0.126) for ELISA.
Conclusions:
The results obtained indicate that, for CLIA assays, it might be possible to define thresholds that improve the negative likelihood ratio. Thus, a negative test result enables the identification of subjects at risk of being infected, who should then be closely monitored over time with a view to preventing further viral spread. Redefined thresholds, in addition, improved the overall inter-assay agreement, paving the way to a better harmonization of serologic tests.
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