Serological Testing for SARS-CoV-2 IgM/IgG Antibody Detection – Combating the COVID-19 Crisis

IgM and IgG antibodies are the most commonly employed biomarkers of early- and late-stage infectious diseases, respectively. As the initial antibody generated by the body’s immune defenses, around the first appearance of symptoms (following the 2-14 day incubation period), IgM is a sign of acute infection. The IgM antibodies will eventually dissipate after about one month. With disease progression, IgG antibodies are subsequently released, approximately one week after symptoms appear, and can remain in circulation for an extended time period, even after complete elimination of the pathogen. Positive blood can be used as an indicator of previous and current infection. Thus, tests for detecting SARS-CoV-2 IgM and IgG antibodies are of great clinical importance and can aid in stemming the large-scale transmission of COVID-19.

How SARS-CoV-2 antibody-based tests work

Serological testing for IgM and IgG antibodies against the SARS-CoV-2 virus is performed with a lateral flow immunoassay that can simultaneously detect both antibody isotypes. All essential assay reagents (recombinant viral antigen; anti-IgM and anti-IgG detection antibodies) are immobilized at specific sites on a strip of nitrocellulose membrane that is encased within a small, solid, rectangular cartridge. Clinical sample (plasma, serum, whole blood, finger prick) is applied to the sample well situated at one end of the cartridge. The sample then traverses the test strip via capillary force. As the sample passes through, any SARS-CoV-2 IgG and IgM antibodies present in the sample will bind the antigen. The resulting antigen-antibody complexes that form will continue to travel across the strip until they are captured by the corresponding anti-IgM and anti-IgG antibodies (labeled as “M” and “G” below), generating a positive signal within the result window in the form of a magenta-colored band.

Interpreting the immunoassay results

The results can provide useful information regarding the stage of infection as well as the history of exposure. A positive result for IgM antibodies is indicative of an active infection with the SARS-CoV-2 virus, and immediate patient quarantine would be recommended. A positive result for IgG antibodies signifies either an active case or recovery from a previous infection. A negative result from a symptomatic patient would necessitate further testing for the viral RNA.

Benefits of using serological tests for SARS-CoV-2 antibody detection

Immunoassays for detecting SARS-CoV-2 IgM and IgG antibodies in blood samples are an easy and convenient way to quickly screen large numbers of patients suspected of contracting COVID-19.

• Fast results
  These single-step assays feature a rapid turnaround time. Results can be obtained in just 3-15 minutes from the moment of sample application, with the variation in time dependent on viral titers and antibody concentrations.


• Simple to use
  No expensive instrumentation, lengthy and time-consuming protocols, specialized technical expertise, or trained personnel are required to conduct the assay. The sample is simply mixed beforehand with a particular buffer, which is supplied with the test cartridge in a kit format, and the mixture is then added to the sample well.


• Built-in controls
  A quality control (labeled as “C” in the figure above), consisting of an unrelated antibody isotype and its associated detection antibody, is automatically incorporated into the assay to ensure proper device functionality and to verify the results.


• Easy to interpret
  Qualitative detection of SARS-CoV-2 IgM and IgG antibodies can easily be determined by the presence of colored bands, akin to a home pregnancy kit.

High demand for serological SARS-CoV-2 immunoassay kits

Under the FDA’s emergency use guidelines published March 16, 2020, SARS-CoV-2 antibody test kits have been preemptively permitted for expedited release and usage. As the COVID-19 crisis has officially reached pandemic proportions, there is an urgent need for these kits by hospitals, clinics, and test labs for swiftly and accurately identifying infected individuals, in order to facilitate the containment of disease spreading and the timely treatment of patients. Although serological immunoassays can identify both symptomatic and asymptomatic carriers of the SARS-CoV-2 virus, it is essential to bear in mind that their results should not be the sole basis for diagnosing COVID-19. Results should always be assessed in conjunction with clinical observations and additional testing methods such as rRT-PCR that precisely target elements of the viral genome. A combination of clinical symptoms, patient history, epidemiological studies, and laboratory testing is necessary for a more comprehensive diagnosis.