通过对169例2019年冠状病毒病（COVID-19）患者的IgM和IgG抗体检测数据进行分析，以评价胶体金法和化学发光法在临床表现上的差异。在本研究中，化学发光法检测IgM抗体的阳性转化早于胶体金法（约早于1～2天），在不同疾病阶段的阳性转化率较高，且阳性率下降的趋势晚于胶体金法。对于IgG抗体，化学发光法比胶体金法阳性转化早，阳性率上升快。发病后35天内，IgG检测未见明显的转阴趋势。虽然胶体金法的灵敏度一般低于化学发光法，但它具有周转时间短、操作简单、无需特殊设备等优点。
这两种方法可根据不同的实验室条件选择。合理了解不同方法试剂的性能，有助于临床疾病的有效诊断，有助于COVID-19进展的诊断，抗体的动态变化将为其提供可靠的依据。
Abstract
The detection data of IgM and IgG antibodies in 169 patients with coronavirus disease‐2019 (COVID‐19) were analyzed to evaluate differences in clinical performance between the colloidal gold method and chemiluminescence method. In this study, chemiluminescence detection of IgM antibody showed a positive conversion earlier (about 1‐2 days earlier), positive conversion rates higher in different stages of disease, and a trend of declining positive rate later than colloidal gold method. For IgG antibody, the chemiluminescence method showed a positive conversion earlier and the positive rate climbing more quickly than the colloidal gold method. No obvious negative‐converting tendency of IgG detection was observed within 35 days after the onset of disease. Although colloidal gold method is generally less sensitive than chemiluminescence method, it shows advantages of shorter turn‐around time, more simple procedure, and no special equipment required. The two methodologies can be chosen according to different laboratory conditions.
A reasonable understanding of the performance of reagents with different methodologies can help in clinical disease diagnosis effectively and assist in the diagnosis of the progression of COVID‐19, for which the dynamic changes of antibody will provide reliable evidence.
1 INTRODUCTION
Currently, the worldwide outbreak of coronavirus disease‐2019 (COVID‐19) has become a public health event of international concern.1 Effective and timely detection of novel coronavirus (severe acute respiratory syndrome coronavirus 2 [SARS‐CoV‐2]) infections will help patients to access timely treatment, prevent further transmission, and ultimately achieve effective control of the epidemic. At present, the diagnosis of SARS‐CoV‐2 infection mainly relies on the detection of viral nucleic acid in upper and lower respiratory tract samples.2-4 However, due to the uneven sampling quality of the respiratory tract samples, especially upper respiratory tract samples, the different viral load of different respiratory tract samples and, at the same time, the insufficient understanding of the characteristics of the spread of SARS‐CoV‐2, nucleic acid tests are frequently reported as false negatives.5-8 If other clinical and laboratory diagnostic methods can be effectively combined, it will help to ensure the timely diagnosis and timely treatment of diseases.9, 10 Serological testing, as a common method, plays an important role in the diagnosis of many pathogen infections. Moreover, the serological tests require more simple procedure and need no special equipment. The standard blood sample collection process ensures the quality of subsequent antibody detection and reduces the risk of virus transmission. With the good detection performance, serological testing can be used as supplementary diagnosis of COVID‐19 suspect cases with nucleic acid negative.11
The human body will produce specific antibodies after the virus invades. The specific IgM antibody appears first, and then the titer of IgG antibody will continue to rise. Serological tests indirectly determine whether there is a viral infection by detecting the presence and changes of specific antibody in blood samples.
At present, during the COVID‐19 epidemic, research on antibody production and changes in patients of COVID‐19 is lack of systematization, and it is difficult to acquire clinical data of large‐scale cohort studies when clinical diagnosis and treatment are in emergency condition. In the clinical trials for the purpose of premarket registration, the SARS‐CoV‐2 antibody detection kits with different methodologies in China were evaluated for the clinical performance by adopting a unified clinical trial protocol based on the requirements of the published “Key Points of Technical Review for Registration of SARS‐CoV‐2 Antigen/Antibody Detection Reagents (Trial version).”12 These clinical trials included not only the data for the evaluation of sensitivity and specificity of the reagents but also the research data of the continuous monitoring of enrolled subjects at different time points of disease. Summarizing the data of serial monitoring in the clinical research, and investigating the positive rate of IgM and IgG antibodies at different time points in the course of SARS‐CoV‐2 infection by reagents with different methodologies will have a positive effect on understanding the changes and outcomes of SARS‐CoV‐2‐related antibodies after human infection, the performance of different antibody detection methodologies, and thus further clarifying the role and significance of different serological detection methods in the diagnosis of COVID‐19.
It should be emphasized that all the clinical trials mentioned here have been conducted in compliance with the consistent protocol according to the “Key Points of Technical Review for Registration of SARS‐CoV‐2 Antigen/Antibody Detection Reagents (Trial version),”12 issued by the Center for Medical Device Evaluation of National Medical Products Administration of China, as a result of which the clinical trial inclusion criteria, definition of the stage of disease and the test result reporting methods are all consistent among the different clinical trials, so it is acceptable to conduct comprehensive analysis with the data collected from all these clinical trials.
2 MATERIALS AND METHODS
Based on the clinical trials of four SARS‐CoV‐2 antibody detection kits submitted and confirmed for registration in China between February 2020 and May 2020, including both colloidal gold method and chemiluminescence method, multitime‐point surveillance data with the information of sampling time were collected and analyzed in this study, to observe the production and conversion of SARS‐CoV‐2‐specific antibodies and evaluate the positive rates of antibodies detected by reagents with different methodologies.
The clinical trials were conducted at seven clinical institutions in compliance with the consistent protocol based on the “Key Points of Technical Review for Registration of SARS‐CoV‐2 Antigen/Antibody Detection Reagents (Trial version).”12 All the clinical trials complied with the provisions of the Declaration of Helsinki and the International Conference on Harmonization on the clinical trial management and were approved by the ethical review committee of clinical trial institutions.
This study includes the continuous monitoring data of IgM and IgG in 169 patients with COVID‐19 from the sample sets of the clinical trials mentioned above. All the enrolled patients were confirmed according to the valid version of “Diagnosis and Treatment Protocol for Novel Coronavirus Pneumonia”13 issued by the National Health Commission of China. Details about the inclusion criteria are shown in part 2.2.
In addition to the investigation of the multitime‐point surveillance data included in this study, the clinical trials mentioned above were also conducted to evaluate the sensitivity and specificity of the four reagents with the samples of COVID‐19 confirmed cases and excluded cases. It was demonstrated that there was no cross reaction with other respiratory viruses, including other coronaviruses for these four reagents (data not shown). All the confirmed cases and excluded cases were diagnosed according to the “Diagnosis and Treatment Protocol for Novel Coronavirus Pneumonia.”13
2.1 Reagents and instruments
SARS‐CoV‐2 IgM and IgG antibody chemiluminescence detection kits were from Maccura Biotechnology Co, Ltd and Bioscience (Tianjin) Diagnostic Technology Co, Ltd. They finished the tests with the chemiluminescence immunoassay instruments specified in the manuals of the in‐vitro Diagnostic (IVD) kits; SARS‐CoV‐2 colloidal gold test kits came from Innovita (Tangshan) Biological Technology Co, Ltd and Zhuhai Livzon Diagnostics Inc, of which the test process and test result interpretation did not require any test instruments (Table 1).
Table 1. Information for the SARS‐CoV‐2 IgM and IgG antibody detection kits
