COVID 19 Testing:
IgG, IgM, IgA Antibody Tests
Significance of the Test:
Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2, previously called 2019-nCoV) belongs to the family of coronaviruses and, like SARS-CoV, is classified in the genus Betacoronavirus . The new coronavirus originated in China in the city of Wuhan, Hubei province. It caused an infection wave, which has spread rapidly within the country and worldwide [2, 3]. Just a few days after the first report about patients with pneumonia of unclear origin, the causative pathogen was identified as SARS-CoV-2 [2-4].
SARS-CoV-2 is predominantly transmitted by droplet infection via coughing or sneezing and through close contact with infected patients [2, 3, 5].
The incubation time of SARS-CoV is three to seven, maximally 14 days . The symptoms of SARS-CoV-2 infection are fever, coughing, breathing difficulties and fatigue [2, 3, 5]. In most patients the infection manifests with symptoms of a mild febrile illness with irregular lung infiltrates. Some patients, especially elderly or chronically ill patients, develop severe acute respiratory distress syndrome (ARDS). The disease is fatal in around 3% of cases [2, 3, 5]. In February 2020, the disease caused by SARS-CoV-2 was named COVID-19 by the WHO.
Suitable methods for diagnosis of SARS-CoV-2 infections are direct detection of the virus RNA by polymerase chain reaction (PCR) primarily in sample material from the upper (smear) or lower respiratory tract (bronchoalveolar lavage fluid, tracheal secretion, sputum, nasopharyngeal secretion, oropharyngeal secretion, etc) and the detection of antibodies against SARS-CoV-2 in blood. The determination of antibodies enables confirmation of SARS-CoV-2 infection in patients with typical symptoms and in suspected cases without symptoms. It also contributes to monitoring and outbreak control.
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Comment for the report:
In general, detectable IgM antibodies are developed within 5 to 7 days after infection and usually remain detectable for 2 to 4 months. Studies of COVCID 19 antibodies are sparse. Limited data that is available show varying of the antibody responses to COVID 19 is based on the study.
In a study from Beijing, China, (Guo,2020) the median duration of IgM and IgA antibody detection were 5 days (while IgG was detected on 14 days after symptom onset, with a positive rate of 85.4%, 92.7% and 77.9% respectively.
In another study by Zheng et al., IgM antibodies start increasing at around day 9 and peaked at day 18. SARS-CoV-2 specific IgG begins increasing between day 9 to 15 and slowly increased during day 15 to 39. The positive rate for IgG reached 100% around 20 days after symptoms onset (Zheng, 2020)
Long et al., reported that the median day of seroconversion for both lgG and IgM was 13 days after symptoms onset. Seroconversion of IgM occurred at the same time, or earlier, or later than that of IgG. IgG levels in 100% patients (19/19) entered a platform within 6 days after seroconversion (Long, 2020).
Guo, L., Ren, L., Yang, S., Xiao, M., Chang, D., Yang, F., ... & Zhang, L. (2020). Profiling early humoral response to diagnose novel coronavirus disease (COVID-19). Clinical Infectious Diseases.
Zheng, Z et al. (2020) Proﬁle of Speciﬁc Antibodies to SARS-CoV-2: The First Report Journal of Infection (2020), doi:
Long, Q et al. (2020). Antibody responses to SARS-CoV-2 in COVID-19 patients: the perspective application of serological tests in clinical practice. 10.1101/2020.03.18.20038018.