Performance evaluation of novel fluorescent-based lateral flow immunoassay (LFIA) for rapid detection and quantification of total anti-SARS-CoV-2 S-RBD binding antibodies in infected individuals

Abstract

Background: A vast majority of the commercially available lateral flow immunoassay (LFIA) is used to detect SARS-CoV-2 antibodies qualitatively. Recently, a novel fluorescence-based lateral flow immunoassay (LFIA) test was developed for quantitative measurement of the total binding antibody units (BAUs) (BAU/mL) against SARS-CoV-2 spike protein receptor-binding domain (S-RBD).

Aim: This study aimed to evaluate the performance of the fluorescence LFIA Finecare^TM 2019-nCoV S-RBD test along with its reader (Model No.: FS-113).

Methods: Plasma from 150 reverse trancriptase-PCR (RT-PCR)-confirmed positive individuals and 100 prepandemic samples were tested by Fincare^TM to access sensitivity and specificity. For qualitative and quantitative validation of the FinCare^TM measurements, BAU/mL results of FinCare^TM were compared with results of 2 reference assays: the surrogate virus-neutralizing test (sVNT, GenScript Biotech, USA) and the VIDAS®3 automated assay (BioMérieux, France).

Results: Finecare^TM showed 92% sensitivity and 100% specificity compared with PCR. Cohen's Kappa statistic denoted moderate and excellent agreement with sVNT and VIDAS®3, with values being 0.557 (95% CI: 0.32-0.78) and 0.731 (95% CI: 0.51-0.95), respectively. A strong correlation was observed between Finecare^TM/sVNT (r = 0.7, p < 0.0001) and Finecare^TM/VIDAS®3 (r = 0.8, p < 0.0001).

Conclusion: Finecare^TM is a reliable assay and can be used as a surrogate to assess binding and neutralizing antibody response after infection or vaccination, particularly in none or small laboratory settings.

Keywords: COVID-19; Fluorescence immunoassay; Lateral Flow Assay; SARS-CoV-2; Serology.

Figure 1

Correlation analysis of the assays standardized readings obtained by each immunoassay. (A) Correlation plot of Finecare^TM with the sVNT. (B) Correlation plot of Finecare^TM with VIDAS®3. Pearson's correlation coefficient (r) and p-value are indicated. Pearson's r of 0–0.19 is regarded as very weak, 0.2–0.39 as weak, 0.40–0.59 as moderate, 0.6–0.79 as strong, and 0.8–1 as very strong correlation, but these are rather arbitrary limits, and the context of the results should be considered. Data are presented for 150 RT-PCR–confirmed SARS-CoV-2–positive samples. BAU, binding antibody unit; RT-PCR, reverse transcriptase–PCR; sVNT, surrogate virus-neutralizing test.

Figure 2

ROC curve for Finecare 2019-nCoV RBD Antibody Test. An AUC of 0.9–1.0 is considered excellent, 0.8–0.9 is considered very good, 0.7–0.8 is considered good, 0.6–0.7 is considered sufficient, 0.5–0.6 is considered bad, and <0.5 is considered not useful. AUC, area under the curve; ROC, receiver Operating Characteristic.