SARS-CoV2 (COVID-19) IgG Antibody ELISA test

  • SARS-CoV-2, the virus that causes COVID-19, continues to spread in India and around the world, straining the capacity of healthcare systems to treat patients with the infection.
  • The timely and accurate diagnosis of the SARS-CoV-2 infection is the cornerstone to treat patients, to limit further spread of the virus and ultimately to eliminate the virus from human society.
  • Diagnosis of current SARS-CoV-2 infection relies mainly on molecular testing (RT-PCR) by detecting viral RNA in the nasopharyngeal/oropharyngeal swabs.
  • Assessment of antibodies to SARS-CoV-2 virus in the population aids in the understanding of disease spread and may support the assessment of immunity.
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Antibody testing

  • Antibody or serology testing is used to detect IgM, IgA, IgG, or total antibodies in blood
  • Studies in SARS–CoV-2, suggests that IgG production occurs between 7 and 11 days post-exposure to the virus
  • IgG production generally continues to rise for 28 to 35 days after symptom onset, peaking around or after clinical recovery
  • Since there is natural delay, antibody testing is not useful in the acute phase of the illness
  • IgG is the most abundant antibody isotype in the blood, accounting for 70 to 75% of human immunoglobulins (antibodies)
  • IgG is largely responsible for long-term immunity after infection or vaccination

Advantage of IgG antibody testing

  • To help determine prior exposure to the virus including in asymptomatic individual
  • To identify potential donors of convalescent plasma
  • For epidemiological purposes including establishing prevalence of disease in populations
  • This test may aid in verifying effectiveness of vaccines

SARS-CoV2 (COVID-19) IgG antibody test

It is an ELISA (Enzyme linked immunosorbent assay) based test for semi-quantitative detection of anti-IgG antibodies against SARS-CoV2 virus in human serum and plasma samples.

The kit utilizes recombinant proteins of SARS-CoV2 i.e., Spike 2 and nucleoprotein for detection of anti-COVID antibodies.

The outcome of test result is expressed in as a numerical index value, to indicate the baseline which enables clinicians to study the dynamics of immune response in infected person with respect to time.

It is used as an adjunct to COVID-19 RT-PCR tests to aid in clinical assessment and not for diagnosis.

Individuals typically begin to develop antibodies 1-3 weeks after symptoms begin, so this test will be usually used about 14-21 days following the start of symptoms.

Limitations

  • A positive test result cannot differentiate between past or present SARS-CoV2 infection and infections due to other coronaviruses, such as SARS-CoV-1, MERS-CoV, HKU1, 229E, NL63, or OC43
  • SARS-CoV-2 IgG test is not useful for diagnosis of acute infection
  • Results obtained with the assay may show interlaboratory variations due to differences in target antigen used for the test
  • Test results should not be interpreted as an indicator for protection from reinfection

Specimen type, collection and transportation

Specimen
Whole blood (3ml) or serum (1ml) or plasma samples (1ml)
Collection
Whole blood can be collected in potassium EDTA tube or plain tubes. Serum or plasma must be separated within 6 hours of collection
Transportation
Whole blood, plasma and serum can be transported at 2-8°C within 24 hours of collection. If there is delay of more than 24 hours in transportation, serum or plasma should be stored in -20°C and transported in frozen condition

Test details

Test
SARS-CoV2 (COVID-19) IgG antibody test
Test Code
MGM1805
TAT
24 Hours after sample is received in the lab

References

  • Zhu, N. et al. A Novel Coronavirus from Patients with Pneumonia in China, 2019. N Engl J Med 382, 727-733, https://doi.org/10.1056/NEJM oa2001017 (2020)
  • Jacofsky D, Jacofsky EM, Jacofsky M. Understanding Antibody Testing for COVID-19. J Arthroplasty. 2020;35(7S):S74-S81. doi:10.1016/j.arth.2020.04.055