Discussion == We measured serum antibody levels in sera collected from healthy medical staff and acutely ill hospitalized individuals with COVID-19 using four assays. than that for the S-IgG (6.9% [4.3%10.4%]) assay, even though difference was not statistically significant (p = 0.150). The levels of S-IgM antibodies and the three others peaked on weeks 3 and 5, respectively. All four assays showed high specificities (>99%). == Conclusions == All four assays had good specificities and were suitable for seropositivity detection after week 3 of sign onset. Assays of IgM only or total Ig (comprising IgM) were better than those of IgG only as an adjunct serological test for early-stage COVID-19 analysis, albeit the use of a serological assay only is insufficient. Keywords:COVID-19, Immunoglobulin, SARS-CoV-2, Seroconversion, Serology Abbreviations:Light, loop-mediated isothermal amplification; CI, confidence interval; RT-PCR, reverse transcription polymerase chain reaction; COVID-19, coronavirus disease; SARS-CoV-2, severe acute respiratory syndrome coronavirus 2; IQR, interquartile range == 1. Intro == Severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2)recognized in December 2019 in Wuhan, Hubei, Chinacauses coronavirus disease (COVID-19), which ranges in severity from an asymptomatic illness to lethal viral pneumonia. Quick, highly accurate diagnostic tests, which are important for controlling the COVID-19 pandemic, have been developed. The standard test for diagnosing acute-phase SARS-CoV-2 illness is a genetic test that detects SARS-CoV-2 RNA by reverse transcription polymerase chain reaction (RT-PCR) or loop-mediated isothermal amplification (Light) in nose or pharyngeal swabs or saliva specimens. However, these checks may generate false-negative results actually during an acute-phase symptomatic illness [1]. Furthermore, although some individuals infected with SARS-CoV-2 are asymptomatic [[2],[3],[4]], they can potentially spread the infection. Thus, genetic checks cannot ascertain the actual state of the infection in some populations [5]. Hence, many manufacturers have developed a wide range of SARS-CoV-2 antibody checks, and many worldwide studies have been performed using homemade or research-use only enzyme-linked immunosorbent assays [[5],[6],[7],[8]]. The abovementioned assays can detect a wide variety of immunoglobulin (Ig) subclasses, such as IgA, IgM, IgG, and total Ig that focuses on proteins like nucleocapsid or spike protein. These serological antibody checks have a variety of potential uses, including the analysis of acute PRKACA conditions, dedication of disease prevalence in certain populations, and understanding antibody production in the vaccination-induced immune response. There have been several reports on antibody screening for individuals in the acute phase of COVID-19 [[5],[6],[7],[8]]; however, studies on antibody levels during the early post-onset period, i.e., the first few days after the onset of COVID-19 symptoms, are limited. Consequently, it is important to understand the styles in antibody levels among patients during the acute phase of COVID-19. This study aimed to determine the antibody response to SARS-CoV-2 nucleocapsid and spike proteins using four automated immunoassays to detect IgM, IgG, and total Ig antibodies among individuals with COVID-19 in Japan. == 2. Individuals and methods == == 2.1. Study design and establishing == This multicenter retrospective cross-sectional study was carried out in the following four academic teaching private hospitals that treated individuals with COVID-19 in Japan: Shonan Fujisawa Tokushukai Hospital (Kanagawa), Shonan Kamakura General Hospital (Kanagawa), Chiba-Nishi General Hospital (Chiba), and Yao Tokushukai General Hospital (Osaka). In Japan, the 1st case of COVID-19 was diagnosed in January 2020, and the 1st Niraparib hydrochloride wave of illness spread nationwide soon thereafter. At this time, we began receiving inpatients with COVID-19. In April 2020, the government declared a state of emergency as the 1st wave peaked in mid-April and ended at the end of May. The second wave peaked in mid-August and ended in September. == 2.2. Participants and sample collection == The study enrolled all consecutive adult individuals with COVID-19 who have been admitted between February and December 2020 to any of the four private hospitals mentioned above who met the following inclusion criteria: (1) over the age of 20 years; (2) confirmed to have SARS-CoV-2 illness by real-time PCR or Light using respiratory tract, nasal, pharyngeal, and/or saliva Niraparib hydrochloride specimens; and (3) have surplus serum specimens available. When multiple samples were available from your same patient for the periods described below, the one that was collected 1st was used: every 3 days from the day of onset to day time 29 post-onset, and every 6 days from days 3041 post-onset. Niraparib hydrochloride The medical COVID-19 status of each patient was classified using a five-category ordinal level based on the maximum respiratory support required.