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. 2021 Feb;27(2):289.e1-289.e4.
doi: 10.1016/j.cmi.2020.09.057. Epub 2020 Oct 5.

Accuracy of a nucleocapsid protein antigen rapid test in the diagnosis of SARS-CoV-2 infection

Bo Diao  1 , Kun Wen  2 , Ji Zhang  3 , Jian Chen  3 , Chao Han  3 , Yongwen Chen  3 , Shufeng Wang  3 , Guohong Deng  4 , Hongwei Zhou  5 , Yuzhang Wu  6
Affiliations

Accuracy of a nucleocapsid protein antigen rapid test in the diagnosis of SARS-CoV-2 infection

Bo Diao et al. Clin Microbiol Infect. 2021 Feb.

Abstract

Objectives: Rapid, reliable and easy-to-implement diagnostics that can be adapted in early severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) diagnosis are critical to combat the epidemic. SARS-CoV-2 nucleocapsid protein (NP) is an ideal target for viral antigen-based detection. A rapid and convenient method was developed based on fluorescence immunochromatographic (FIC) assay to detect the SARS-CoV-2 NP antigen. However, the accuracy of this diagnostic method needs to be examined.

Methods: This prospective study was carried out between 10 and 15 February 2020 in seven hospitals in Wuhan and one hospital in Chongqing, China. Participants with clinically suspected SARS-CoV-2 infection were enrolled. NP antigen testing by FIC assay and nucleic acid (NA) testing by real-time reverse transcriptase PCR (RT-PCR) were performed simultaneously in a blinded manner with the same nasopharyngeal swab sample. The diagnostic accuracy of NP antigen testing was calculated by taking NA testing of RT-PCR as the reference standard, in which samples with a cycle threshold (Ct) value of ≤40 were interpreted as positive for SARS-CoV-2.

Results: A total of 253 participants were enrolled; two participants were excluded from the analyses because of invalid NP testing results. Of 251 participants (99.2%) included in the diagnostic accuracy analysis, 201 (80.1%) had a Ct value of ≤40. With Ct value 40 as the cutoff of NA testing, the sensitivity, specificity and percentage agreement of the FIC assay was 75.6% (95% confidence interval, 69.0-81.3), 100% (95% confidence interval, 91.1-100) and 80.5% (95% confidence interval, 75.1-84.9) respectively.

Conclusions: With RT-PCR assay as the reference standard, NP antigen testing by FIC assay shows high specificity and relatively high sensitivity in SARS-CoV-2 diagnosis in the early phase of infection.

Keywords: Antigen detection; Diagnosis; Fluorescence immunochromatographic assay; Nucleocapsid protein; SARS-CoV-2.

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