Early data on the performance of a combined SARS-CoV-2 spike-nucleocapsid antibody lateral flow immunoassay device compared with a nucleocapsid-only device
Introduction
There is a critical need for reliable antibody detection methods in order to study and evaluate the public health and clinical response to the ongoing coronavirus disease 2019 (COVID-19) pandemic.1 Lateral flow immunoassay (LFIA) devices potentially offer the prospect of rapid point-of-care testing (POCT), but the performance of these devices must be evaluated for robustness before they can be adopted for routine clinical and public health use.2–4 Furthermore, as of when this study was conducted in May 2020, there were no published studies of these LFIA devices for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) antibodies.
Materials and methods
In the present study, anonymised, residual stored plasma and serum specimens from SARS-CoV-2 RNA-positive (n=131) and presumed (pre-COVID-19) or RNA-negative (n=37) patients were taken from various time points with respect to the onset of symptoms. All 168 anonymised specimens were tested for IgM and IgG using the Hangzhou AllTest 2019-nCoV IgG/IgM rapid test cassette and the Abbexa COVID-19 IgG/IgM rapid test kit.
Results and discussion
There were great disparities in the responses to IgM and IgG between the two devices, but sensitivity for IgG detection improved over time from symptom onset (Fig 1). IgM sensitivity ranged from 12.90% (95% confidence interval (CI) 3.63–29.83) to 68% (95% CI 46.50–85.05), depending on the date of symptom onset and the device. Regarding IgG, the Abbexa device outperformed the Hangzhou device at all cumulative timeline brackets, with sensitivity of 97.87% (95% CI 88.71–99.95) for Abbexa versus 68.09% (95% CI 52.88–80.91) for Hangzhou for samples beyond 21 days from symptom onset (Table 1). Day 21 was therefore chosen as the cut-off for ascertaining test performance characteristics, beyond which the specificity was 100% (95% CI 90.51–100.00) for both Abbexa and 97.30 (95% CI 85.84–99.93) for Hangzhou. Negative predictive value was 0.97 (95% CI 0.84–1.00) for Abbexa versus 0.71 (95% CI 0.61–0.79) for Hangzhou.
Conclusion
Based on this limited dataset, the performance characteristics of the Abbexa LFIA device were substantially better than those of the Hangzhou device. Applying a 21-day cut-off for the Abbexa device revealed performance that was very close to meeting the minimum sensitivity and specificity thresholds (98%) set by the UK Medicines and Healthcare Products Regulatory Agency (MHRA).5 The Abbexa device captures antibodies against both SARS-CoV-2 spike and nucleocapsid proteins, as opposed to Hangzhou, which targets only the nucleocapsid protein.2,6–8 We therefore propose that spike glycoprotein antibodies be considered as an additional moiety to test as part of the standard diagnostic approach towards SARS-CoV-2 antibody profiling9–10 to improve clinical sensitivity and potentially specificity, pending follow-up studies to confirm this approach.
Conflicts of interest
None declared.
- © Royal College of Physicians 2021. All rights reserved.
References
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- Li Z
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- Abbexa
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- Vashist S
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- Department of Health and Social Care
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- Medicines and Healthcare products Regulatory Agency
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- Egner W
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