IgM and IgG Antibody Levels in Patients with COVID-19 in South Andhra Pradesh

Abstract

BACKGROUND Coronavirus disease - 19 (COVID-19) is an infectious disease caused by a newly discovered coronavirus, severe acute respiratory syndrome coronavirus 2 (SARSCoV-2). Anti-SARS-CoV-2 IgM and IgG antibodies can be detected in almost all patients of COVID-19. We sought to evaluate the antibody responses in COVID19 patients and also analyse their potential role in disease prognostication. METHODS All consecutive COVID-19 patients, between ages 20 - 65 years, encountered between April and July 2020 were included and compared to age-matched controls. Severity of the SARS-CoV-2 infection was categorized as none, mild and severe, based on the presence of symptoms, oxygen saturation and need for respiratory support. Serum levels of IgM and IgG antibody assays were obtained, using chemiluminescence immunoassay, after the 2nd week of presentation (range 14 - 60 days). Antibody titres above 10 AU/ml were taken as elevated. RESULTS Of 50 eligible patients, majority (40/50, 80 %) had mild symptoms and oxygen saturations above 94 %. Of the remainder, 10 % (5/50) had severe infection with need for either high flow nasal cannula oxygen or mechanical ventilation while the remainder (10 %; 5/50) were asymptomatic. IgM and IgG seroconversion were noted in almost all COVID-19 patients (46/50, 92 %) compared to healthy controls. While elevated IgG antibody levels were noted in 76 % (38/50), combined elevation of IgM and IgG antibodies is seen in 16 % (8/50) of patients. Seroconversion was markedly profound in patients with severe infection than those with mild infection. Also, greater seroconversion was noted after 21 days of testing compared to 14th day, especially for IgG. CONCLUSIONS Antibody seroconversion to SARS-CoV-2 occurred in majority of patients with COVID-19, with most salient increase in the IgG antibody levels. Antibody titres correlated directly to the disease severity, suggestive of the potential value of antibodies not only in diagnosis but also in prognostication. KEYWORDS COVID-19, Chemiluminescence Immunoassay, Invasive Mechanical Ventilation, High Flow Nasal Oxygen