Antibody detection may play an important role in the diagnosis of COVID-19
By Denise Baez
NEW YORK -- April 21, 2020 -- The antibodies against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) can be detected in the middle and later stage of the illness using an enzyme-linked immunosorbent assay (ELISA), according to a study published in Clinical Infectious Diseases.
The findings suggest that antibody detection may play an important role in the diagnosis of coronavirus disease 2019 (COVID-19) as complement approach for viral nucleic acid assays.
Fei Xiang, MD, Union Hospital, Tongji Medical College, Wuhan, China, and colleagues evaluated IgM and IgG antibody responses to SARS-CoV-2 virus infection from patients treated at Union Hospital between January 19, 2020, and March 2, 2020. A total of 216 serum samples from 85 patients with confirmed coronavirus disease 2019 (COVID-19) were obtained in different time periods after symptoms onset.
The IgM and IgG antibodies were detected positive as early as on the 4th day after onset. The seropositive rate of IgM increased gradually and IgG was increased sharply on the 12th day after onset.
In the confirmed patients with COVID-19, the sensitivity rate of IgM was 77.3%, specificity was 100%, positive predictive value (PPV) was 100%, negative predictive value (NPV) was 80%, and consistency rate was 88.1%. The respective rates for IgG were 83.3.3%, 95.0%, 94.8%, 83.8%, and 88.9%.
In a different cohort of 24 patients with suspected COVID-19, sensitivity, specificity, PPV, NPV, and consistency rate of IgM were 87.5%, 100%, 100%, 95.2%, and 96.4%. The respective rates for IgG were 70.8%, 96.6%, 85.0%, 89.1%, and 88.1%.
“Specificity and positive predictive value of IgM antibody were very high up to 100%, which indicated that the IgM can be used as a good mark for diagnosis of COVID-19,” the authors wrote. “However, the sensitivity, negative predictive value, and consistency rate of IgM were 73.2%, 80.0% and 88.1%, respectively, indicating that acute infection may still be missed based on seronegative IgM. The specificity negative predictive value and consistency rate of IgG were 95.0%, 94.8% and 88.9%, respectively, which means patients can be diagnosed as COVID-19 pneumonia [based] on seropositive IgG.”
“Both seropositive antibodies demonstrate outstanding specificity and PPV, it [suggests] that seropositive IgM and/or IgG can help to establish the diagnosis of COVID-19 pneumonia, especially in patients with a long course,” the authors continued. “To avoid misdiagnosis, patients with early seronegative antibodies should be retested after 10 days of onset.”
“Detection of antibodies against COVID-19 [based on] ELISA appears to be a valid approach to serodiagnosis of COVID-19 pneumonia,” the authors wrote. “The specific circulating antibody can be uniformly detected, therefore avoiding false-negative results due to sampling or potential absence of viruses in the respiratory system. COVID-19 pneumonia can be diagnosed [based] on seropositive of specific antibodies as an alternative to viral nucleic acid detection with clear advantages.”