Analytical performance of lateral flow immunoassay for SARS-CoV-2 exposure screening on venous and capillary blood samples

Abstract

Objectives: We validate the use of a lateral flow immunoassay (LFI) intended for rapid screening and qualitative detection of anti-SARS-CoV-2 IgM and IgG in serum, plasma, and whole blood, and compare results with ELISA. We also seek to establish the value of LFI testing on blood obtained from a capillary blood sample.

Methods: Samples collected by venous blood draw and finger stick were obtained from patients with SARS-CoV-2 detected by RT-qPCR and control patients. Samples were tested with Biolidics 2019-nCoV IgG/IgM Detection Kit lateral flow immunoassay, and antibody calls were compared with ELISA.

Results: Biolidics LFI showed clinical sensitivity of 92% with venous blood at 7 days after PCR diagnosis of SARS-CoV-2. Test specificity was 92% for IgM and 100% for IgG. There was no significant difference in detecting IgM and IgG with Biolidics LFI and ELISA at D0 and D7 (p = 1.00), except for detection of IgM at D7 (p = 0.04). Capillary blood of SARS-CoV-2 patients showed 93% sensitivity for antibody detection.

Conclusions: Clinical performance of Biolidics 2019-nCoV IgG/IgM Detection Kit is comparable to ELISA and was consistent across sample types. This provides an opportunity for decentralized rapid testing and may allow point-of-care and longitudinal self-testing for the presence of anti-SARS-CoV-2 antibodies.

Keywords: COVID-19; Lateral flow immunoassay; SARS-CoV-2; Serology; Validation.

Fig. 1

Visual interpretation of 2019-nCoV IgG/IgM Detection Kit (Colloidal Gold). Any intensity of red color change in the IgM and IgG test regions is considered a positive result. Plasma results: A. IgM (+) IgG (−), B. IgM (+) IgG (−), C. IgM (+) IgG (+), D. IgM (−) IgG (+), E. IgM (+) IgG (+), F. IgM (−) IgG (−). Capillary blood results: G. IgM (+) IgG (+), H. IgM (−) IgG (+), I. IgM (−) IgG (+), J. IgM (−) IgG (−). (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

Fig. 2

Sequential Antibody Detection. A. Samples of 11 patients with SARS-CoV-2 were tested by Biolidics at both D0 and D7 for the presence of IgM and IgG. Samples of 9 patients with SARS-CoV-2 were assessed by ELISA at D0 and D7 for the presence of IgM (B) and IgG (C). Dotted line represents ELISA concentration threshold of positivity (0.3 U/mL for IgM, 0.2 U/mL for IgG). * ELISA results not available for P10 and P24. §P19 was taking immunosuppressant therapy.

Fig. 3

A. Comparison of Biolidics results and ELISA concentration in samples of patients from the pre-COVID19 era, patients with COVID19 tested at D0, and patients with COVID19 tested at D7. (A) IgM and (B) IgG. Red dotted line represents corresponding cut-off values based on ELISA standard curve, 0.3 U/mL for IgM and 0.2 U/mL for IgG. Black dotted line represents the 95% confidence threshold, such that 95% of results that are positive result by Biolidics have an antibody concentration by ELISA higher than or equal to the established threshold. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

Fig. 4

A-B. Biolidics LFI results in six paired venous plasma (A, top row) and whole blood (B, bottom row) samples showing concordant results. Test interpretation by numbered test kits: 31, IgM (+), IgG (+); 32, IgM (+), IgG (+); 33, IgM (−), IgG (+); 34, IgM (−), IgG (−); 35, IgM (−), IgG (+). C. Biolidics LFI results of (left to right) venous whole blood, venous plasma, capillary finger stick at 10 days after PCR diagnosis, and capillary finger stick at 16 days after PCR diagnosis. All 3 sample types at day 10 show IgM (+) and IgG (−), while capillary finger stick at day 16 shows IgM (+) and IgG (+). D. Biolidics LFI with capillary samples of two household members with simultaneous COVID-19. Left image shows IgM (−) and IgG(−) while right image shows IgM (−) and IgG (+).