Sampriti Roy, University of Calcutta
When an obvious cause of the disease is not present, a doctor takes into account the patient’s medical history, age, symptoms, test results and overall health to figure out what is wrong. By doing this and thus correlating different factors, they figure out what is most likely the issue. This is called a clinical correlation.
Recently, an observational cohort study by DeSimone et al. was carried out to evaluate antibody responses in individuals with PCR-confirmed COVID-19, including 48 hospitalized patients diagnosed with COVID-19 by real-time polymerase chain reaction (RT-PCR) at a large tertiary care medical centre in the USA. This was to find out clinical correlations of SARS-CoV-2 antibody responses in patients with COVID-19.
Work done included the following:
- IgM and IgG antibody responses to SARS-CoV-2 were evaluated in patients throughout infection based on onset of symptoms extracted from the medical record (median 14 days, interquartile range 11-18 days).
- A cohort of patients included in the study was of diverse demographics, presenting comorbidities and symptoms.
- To identify other correlates of antibody responses, the association of SARS-CoV-2 antibodies with other laboratory findings was evaluated.
- To control the subjective nature of symptom reporting, antibody results relative to the date of the first positive SARS-CoV-2 RT-PCR result were analysed as a secondary measure of the time of acute infection.
The results found:
- Most patients had detectable SARS-CoV-2 IgM and IgG antibodies after a week following symptom onset, ranging from 8 to 29 days.
- Importantly, only very low levels of IgM or IgG were detected within the first week of infection.
- Nine out of forty-eight individuals (mentioned earlier) did not produce high levels of IgM during infection in this cohort of patients with confirmed cases of COVID-19. This pattern is significant as it might represent a less robust early immune response by individuals with modest symptoms.
- Thirty-nine out of forty-eight individuals were found to develop IgG antibodies against SARS-CoV-2.
- Significant associations of SARS-CoV-2 antibodies with clinical outcomes, including intubation and death were not observed.
- IgM antibodies were associated with higher ALT (Alanine Aminotransferase) levels.
Significance of the study
Understanding the clinical correlations of antibodies produced by infected individuals will be critical for incorporating antibody results in clinical management. This study provides new information about antibody responses to SARS-CoV-2 in a U.S. population concerning individuals who did not develop high levels of SARS-CoV-2 IgM or IgG antibodies.
Limitations of the study:
- Small population-centric; focused at a single tertiary care
- Use of a single serology assay
- At later time points in infection, very few individuals remained hospitalized. Thus, obtaining a large number of samples from late time points was not feasible.
But aside from the limitations, the study concludes that additional studies with a larger cohort of patients will be required to have a more detailed description of the clinical status of patients with low and high levels of SARS-CoV-2 IgM and IgG antibodies and to define accurately how these antibody levels relate to clinical outcomes.
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Source: medRxiv 2020.10.22.20213207; https://doi.org/10.1101/2020.10.22.20213207
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