The Truth about IgM and IgG Antibody/Serology Tests

Serology tests are critical tools for guiding clinical and public health decision making during the COVID-19 pandemic. Serology tests help determine patient immune status in response to a recent infection by identifying antibodies found in the liquid part of blood, called serum or plasma.

Antibodies are proteins produced by the immune system. Immunoglobulin M, or IgM, are the first antibodies produced in response to an infection and are detectable 4-7 days after infection starts.
SARS-CoV-2 IgM antibodies are short-lived and may appear while the virus is still present. A SARS-CoV-2 Immunoglobulin G (IgG) test detects antibodies associated with longer-term immunity.

Recent studies have identified asymptomatic individuals with a negative diagnostic test result and a positive IgM test, suggesting they may have had a recent infection but with low viral load. Both IgM and IgG assays are able to identify antibodies even in asymptomatic individuals. Specifically, the IgM assay may aid in identifying patients with an immune response to SARS-CoV-2 but had negative PCR results.

Serology testing may also help identify individuals with an active infection in the face of PCR diagnostic test shortages. Additionally, IgM assays can be used to provide clinicians with useful information when access to PCR testing is limited or PCR turnaround times are too long.

COVID-19 requires multiple analytic tools to help determine the health status of an individual. High-quality separate antibody assays, such as IgM and IgG specific assays designed to identify antibodies associated with both short-term and long-term immune responses will help us monitor and prevent the spread of the pandemic. Confirming suspected COVID-19 cases as early as possible is critical in isolating patients to slow the spread of disease.

For more information, visit www.BeckmanCoulter.com/Coronavirus