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Quest Diagnostics

IgG and IgG/IgM antibody serology testing

People not presently experiencing signs or symptoms may undergo an IgG or IgG/IgM antibody serology test via blood draw.

The antibody tests from Quest Diagnostics have been authorized by the FDA for use as aids in identifying individuals with an adaptive immune response to SARS-CoV (COVID-19), indicating recent or prior infection, versus the molecular test which is used to help identify an active infection. The FDA has authorized the intended use of these antibody tests as aids in identifying individuals with an adaptive immune response to SARS-CoV-2 (COVID-19), indicating recent or prior infection.1-6

Antibody tests may benefit people at high-risk for being infected or for severe outcomes. Those risks include:

  • Obesity
  • Lung disease or other chronic conditions
  • Elderly
  • Immunocompromised
  • Transplant recipients
  • Underserved individuals
  • Front line healthcare workers

Testing for SARS-CoV-2 can play an important role in the fight against COVID-19, including for individuals who may be asymptomatic, or who are ≥10 days post–SARS-CoV-2 exposure or post–symptom onset.7,8 SARS-CoV-2 antibody testing can be used to:

  • Identify individuals who have been infected with SARS-CoV-2 and have developed an immune response2,3,9-13
  • Assess how many people have been infected with SARS-CoV-2 in a population by identifying individuals who have developed antibodies to the virus9-11
  • Possibly help identify individuals who may be able to donate convalescent plasma as a possible treatment for those who are seriously ill from COVID-199-11

The presence of IgG or IgM antibodies to SARS-CoV-2 may indicate that the patient has developed an immune response to the virus. Although the immune response may protect against reinfection, this has yet to be conclusively established.1,11,12,14,15 It is not known how long antibodies to the virus will protect someone, if at all. Cases of reinfection with COVID-19 have been reported but remain rare.1,11,12,14,15

Insights when they are needed most

At Quest, we know that the accuracy and reliability of SARS-CoV-2 (COVID-19) antibody tests have been under scrutiny at a time when clarity and insights are needed most. Today, the FDA requires companies to submit Emergency Use Authorization (EUA) applications for all antibody tests. The test systems that are used by Quest Diagnostics have been granted EUAs.1-6

The IgG and IgM antibody tests are intended for use as an aid in identifying individuals with an adaptive immune response to SARS-CoV-2, indicating recent or prior infection. Results are for the detection of SARS CoV-2 antibodies. IgG and IgM antibodies to SARS-CoV-2 are generally detectable in blood several days after initial infection, although the duration of time antibodies are present post-infection is not well characterized.

At this time, it is unknown for how long antibodies persist following infection and if the presence of antibodies confers protective immunity.

Individuals may have detectable virus present for several weeks following seroconversion. Negative results do not preclude acute SARS-CoV-2 infection. If acute infection is suspected, molecular testing for SARS-CoV-2 is necessary. The tests should not be used to diagnose acute SARS-CoV-2 infection. False positive results for the test may occur due to cross-reactivity from pre-existing antibodies or other possible causes.

The sensitivity of the test early after infection is unknown. Due to the risk of false positive results, confirmation of positive results should be considered using a second, different IgM assay or an IgG assay. Samples should only be tested for IgM from individuals with 15 days to 30 days post symptom onset. SARS-CoV-2 antibody negative samples collected 15 days or more post symptom onset should be reflexed to a test that detects and reports SARS-CoV-2 IgG.

The results of the semi-quantitative test should not be interpreted as an indication of degree of immunity or protection from reinfection.

Results obtained with this assay may not be used interchangeably with values obtained with different manufacturers’ test methods.11

SARS-CoV-2 Antibody (IgG), Spike, Semi-Quantitative (test code 34499)

A SARS-CoV-2 semi-quantitative IgG test result is interpreted as a positive value at an index4,5 of ≥1.00. This positive result means that an individual has developed an immune response to recent/prior SARS-CoV-2 infection within the limit of detection of the assay.4,5,16,17

A negative semi-quantitative antibody result means that the patient serum specimen had no SARS-CoV-2 spike IgG antibodies, or that the relative level of antibodies in the patient specimen was below the index cutoff.4,5

  • Estimated assay sensitivity is >99.9% for specimens collected at least 15 days post–symptom onset,4,5 based on positive percent agreement (PPA)1 of SARS-CoV-2 IgG serology results among SARS-CoV-2 RNA−positive patients4,5
  • Estimated assay specificity is approximately 99.9%4,5 based on negative percent agreement (NPA)2 assessed by performing cross-reactivity studies utilizing serum specimens positive for antibodies to other respiratory viruses pre– and post–COVID-19 time periods4,5

SARS-CoV-2 Total Antibody, Spike, Semi-Quantitative (test code 39820)

The result of the total semi-quantitative SARS-CoV-2 antibody immunoassay test is reported as positive at an index of ≥0.8 (index detection interval6 0.4-250.0 U/mL). Conversely, a negative result is reported at an index6 of <0.8 U/mL.

SARS-CoV-2 Antibody (IgG), Nucleocapsid, Qualitative  (a component of the IgM/IgG panel, test code 31672) (test code 39749)

This test is used to detect IgG antibodies in serum (blood) samples. The test aids in identifying an immune response to recent or prior natural infection with SARS-CoV-2.

  • Estimated assay sensitivity is >99.6% for specimens collected at least 15 days post–symptom onset,2 based on PPA1 of SARS-CoV-2 IgG serology results among SARS-CoV-2 RNA−positive patients2
  • Estimated assay specificity2 is >99.9%, based on NPA1 assessed by performing cross-reactivity studies utilizing serum specimens positive for antibodies to other respiratory viruses pre– and post–COVID-19 time periods2

SARS-CoV-2 Serology (COVID-19) Antibodies (IgG, IgM), Immunoassay (test code 31672)

Quest only offers SARS-CoV-2 IgM (spike) in a panel that includes a separate IgG (nucleocapsid) determination.2,3 The results from this qualitative test for SARS-CoV-2 IgM can be positive (reactive) or negative (non-reactive).2,13 Separate results are provided for IgG and IgM.

  • Estimated assay sensitivity is 95%2 for specimens collected at least 15 days post–symptom onset,2 based on PPA1 of SARS-CoV-2 IgM serology results on patients who are SARS-CoV-2 RNA–positive2
  • Estimated specificity is >99%2 based on NPA1 assessed by performing SARS-CoV-2 IgM tests on serum specimens positive for antibodies to other respiratory viruses pre– and post–COVID-19 time periods2

For specific clinical performance, please review each test’s “Instructions for Use”:

Siemens Healthcare Diagnostics IgG Semi-Quant (Atellica®)
Abbott Laboratories IgG
Ortho-Clinical IgG
Abbott Laboratories IgM
Siemens Healthcare Diagnostics IgG Semi-Quant (Centaur®)
Roche Diagnostics Inc.
Total Ab (Roche Elecsys®)

References

  1. FDA. EUA authorized serology test performance. Updated April 28, 2021. Accessed May 11, 2021. https://www.fda.gov/medical-devices/emergency-situations-medical-devices/eua-authorized-serology-test-performance
  2. Architect SARS-CoV-2 IgG (nucleocapsid). Package insert. Abbott Laboratories; 2020. Accessed April 7, 2021. https://www.fda.gov/media/137383/download
  3. Architect AdviseDx SARS-CoV-2 IgM (spike). Package insert. Abbott Laboratories; 2020. Accessed April 7, 2021. https://www.fda.gov/media/142940/download
  4. Atellica® IM SARS-CoV-2 IgG (COV2G; spike). Instructions for use. Siemens Healthcare Diagnostics Inc; 2020. Accessed April 7, 2021. https://www.fda.gov/media/140699/download
  5. ADVIA® Centaur® SARS-CoV-2 IgG (COV2G; spike). Instructions for use. Siemens Healthcare Diagnostics Inc; 2020. Accessed April 7, 2021. https://www.fda.gov/media/140704/download
  6. Cobas® Elecsys Anti-SARS-CoV-2 S (spike). Instructions for use. Roche Diagnostics Inc; 2021. Accessed April 7, 2021. https://www.fda.gov/media/144037/download
  7. FDA. Important information on the use of serologic (antibody) tests for COVID-19–letter to health care providers. Updated April 17, 2020. Accessed January 21, 2021. https://www.fda.gov/medical-devices/letters-health-care-providers/important-information-use-serological-antibody-tests-covid-19-letter-health-care-providers
  8. CDC. Interim considerations for COVID-19 vaccination of healthcare personnel and long-term care facility residents. Reviewed December 3, 2020. Accessed April 7, 2021. https://www.cdc.gov/vaccines/hcp/acip-recs/vacc-specific/covid-19/clinical-considerations.html
  9. FDA. FAQs on testing for SARS CoV-2. Updated March 25, 2021. Accessed April 19, 2021. https://www.fda.gov/medical-devices/coronavirus-covid-19-and-medical-devices/faqs-testing-sars-cov-2
  10. Espejo AP, Akgun Y, Al Mana AF, et al. Review of current advances in serologic testing for COVID-19. Am J Clin Pathol. 2020;154(3):293-304. doi:10.1093/ajcp.aqaa112
  11. CDC. Interim guidelines for COVID-19 antibody testing. Updated March 17, 2021. Accessed April 7, 2021. https://www.cdc.gov/coronavirus/2019-ncov/lab/resources/antibody-tests-guidelines
  12. FDA. Fact sheet for healthcare providers: SARS-CoV-2 IgG (nucleocapsid) assay - Abbott Laboratories Inc. Updated December 1, 2020. Accessed April 7, 2021. https://www.fda.gov/media/137381/download
  13. FDA. Fact sheet for healthcare providers: Abbott Laboratories AdviseDx SARS-CoV-2 IgM. Updated October 9, 2020. Accessed April 7, 2021. https://www.fda.gov/media/142938/download
  14. CDC. Reinfection with COVID-19. Updated October 27, 2020. Accessed April 7, 2021. https://www.cdc.gov/coronavirus/2019-ncov/your-health/reinfection.html
  15. Ju B, Zhang Q, Ge J, et al. Human neutralizing antibodies elicited by SARS-CoV-2 infection. Nature. 2020;584(7819):115-119. doi:10.1038/s41586-020-2380-z
  16. FDA. Fact sheet for healthcare providers: Siemens Healthcare Diagnostics Inc Atellica® IM SARS-CoV-2 IgG (COV2G; spike). Updated July 31, 2020. Accessed April 7, 2021. https://www.fda.gov/media/140698/download
  17. FDA. Fact sheet for healthcare providers: Siemens Healthcare Diagnostics Inc ADVIA Centaur® SARS-CoV-2 IgG (COV2G; spike). Updated July 31, 2020. Accessed April 7, 2021. https://www.fda.gov/media/140702/download

The value of antibody testing goes beyond any one individual patient

Reliable antibody tests help public health officials determine prevalence of infection in the community, particularly in underserved populations or populations with limited access to testing.1,2 Knowing the status of the population through antibody testing can provide the following insight and guidance:

Helping to identify an adaptive immune response
A semi-quantitative antibody test can aid in identifying individuals with an adaptive immune response to SARS-CoV-2 (COVID-19), indicating recent or prior infection.

Helping people understand whether they have been previously infected
According to the CDC, SARS-CoV-2 (COVID-19) IgG antibody tests check for antibodies in the blood, which may indicate a prior infection with the virus that causes COVID-19.3

Developing and maintaining ongoing care paths
With new evidence suggesting COVID-19 may be linked to potential long-term medical disorders, understanding an individual’s status can assist in developing and maintaining ongoing care paths.4

Supporting complex diagnoses
Serologic testing should be offered as a method to help support a diagnosis when patients present with late complications of COVID-19 illness, such as multisystem inflammatory syndrome in children.5

Physicians and public health experts have identified potential clinical applications for SARS-CoV-2 serology testing:

  • Clinical assessment of individuals after illness onset
    Data suggest that IgM antibodies can be detected within several days after initial infection and IgG antibodies will be detectable from 7 to 30 days after SARS-CoV-2 symptom onset6
  • Treating high-risk individuals
    Treating individuals who are vulnerable and at higher risk of severe clinical outcomes from COVID-19 (eg, patients with COPD or cardiovascular risks)7
  • Blood donors
    Individuals whose blood contains antibodies may be eligible to serve as blood donors of convalescent plasma, which may provide an avenue for possible treatment for those who are hospitalized due to COVID-198

It is not yet known how long antibodies persist following infection, if the presence of antibodies affords immunity, how long such immunity might last, and whether the presence of antibodies provides full protection from reinfection. Individuals may have detectable virus for several weeks following seroconversion.5,9

Compared to IgG antibodies, IgM antibodies are typically detected earlier, during the acute phase of an infection. In the typical infection cycle, the presence of IgM would suggest a more recent or possibly unresolved infection, while the IgG antibody would suggest a prior infection.

SARS-CoV-2 antibody testing must be ordered by a physician. Patients may make an appointment at a Quest Patient Service Center for this test.

 
References
  1. CDC. Interim guidelines for COVID-19 antibody testing. Updated March 17, 2021. Accessed April 7, 2021. https://www.cdc.gov/coronavirus/2019-ncov/lab/resources/antibody-tests-guidelines.html
  2. Infectious Diseases Society of America. COVID-19 antibody testing primer. Updated May 4, 2020. Accessed February 5, 2021. https://www.idsociety.org/globalassets/idsa/public-health/covid-19/idsa-covid-19-antibody-testing-primer.pdf
  3. CDC. Test for past infection (antibody test). Updated February 2, 2021. Accessed February 5, 2021. https://www.cdc.gov/coronavirus/2019-ncov/testing/serology-overview.html
  4. CDC. Long-term effects of COVID-19. Updated April 8, 2021. Accessed May 5, 2021. https://www.cdc.gov/coronavirus/2019-ncov/long-term-effects.html
  5. CDC. Recommendations for use of serologic tests. Updated November 3, 2020. Accessed May 5, 2021. https://www.cdc.gov/coronavirus/2019-ncov/lab/serology-testing.html
  6. Architect SARS-CoV-2 IgG (nucleocapsid). Package insert. Abbott Laboratories; 2020. Accessed April 7, 2021. https://www.fda.gov/media/137383/download
  7. CDC. Evidence used to update the list of underlying medical conditions that increase a person’s risk of severe illness from COVID-19. Updated March 29, 2021. Accessed May 5, 2021. https://www.cdc.gov/coronavirus/2019-ncov/need-extra-precautions/evidence-table.html
  8. FDA. Investigational COVID-19. Convalescent plasma. Guidance for industry. Issued February 11, 2021. Accessed May 11, 2021. https://www.fda.gov/media/136798/download
  9. FDA. Fact sheet for healthcare providers: Abbott Laboratories. AdviseDx SARS-CoV-2 IgM. Updated October 9, 2020. Accessed April 7, 2021. https://www.fda.gov/media/142938/download

Turnaround time for the SARS-CoV-2 antibody serology tests is typically 1-2 days from the time the specimen is received in our laboratory, but can vary due to high demand.

Quest continues to scale up testing capacity on the serology platform by expanding testing across its network of laboratories and adding other IVD testing platforms.

View Current Turnaround Times for Molecular Testing

All SARS-CoV-2 antibody testing must be ordered by a physician. Healthcare professionals can now order COVID-19 antibody serology testing using the following test codes:

  • SARS-CoV-2 Antibody (IgG), Spike, Semi-Quantitative
  • SARS-CoV-2 Total Antibody, Spike, Semi-Quantitative 
  • SARS-CoV-2 Antibody (IgG), Nucleocapsid, Qualitative
    (a component of the IgM/IgG panel, test code 31672)
  • SARS-CoV-2 Serology (COVID-19) Antibodies (IgG, IgM), Immunoassay

test code 34499
test code 39820
test code 39749

test code 31672

The CDC recommends the use of antibody testing in conjunction with molecular RNA testing to support the clinical assessment of COVID-19 illness in persons who present 9 to 14 days after illness onset.1

Data suggests that IgM antibodies can be detected within several days after initial infection and IgG antibodies will be detectable from 7 to 30 days after SARS-CoV-2 symptom onset.2

It is reasonable to conduct an antibody test after 14 days of being symptom-free because most people will develop an antibody response in that timeframe. Further studies may further define and/or shorten the testing window.

References

 

  1. CDC. Serology testing for COVID-19. Updated November 3, 2020. Accessed April 5, 2021. https://www.cdc.gov/coronavirus/2019-ncov/lab/serology-testing.html
  2. Architect SARS-CoV-2 IgG (nucleocapsid). Package insert. Abbott Laboratories; 2020. Accessed April 7, 2021.https://www.fda.gov/media/137383/download

The SARS-CoV-2 antibody tests have not been validated for diagnosing an active COVID-19 infection. Quest offers the molecular test (test code 39448) for diagnosing an active COVID-19 infection.

IgG Assay

Abbott Laboratories healthcare provider fact sheet (IgG)
Test directory (ordering information)
Ortho-Clinical healthcare provider fact sheet

IgG/IgM Assay

Abbott Laboratories healthcare provider fact sheet (IgM)
Test directory (ordering information)

IgA/IgM/IgG Assay

Roche Diagnostics, Inc. healthcare provider fact sheet (Total Ab)

More information

Patient results brochure
Healthcare provider brochure

Video update on IgG antibody serology testing

Jay G. Wohlgemuth, M.D.
Senior Vice President, R&D, Medical and Chief Medical Officer

Supervised self-collection for molecular (PCR) SARS-CoV-2 RNA (COVID-19) Qualitative NAAT (test code 39448) is now offered in Quest Patient Service Centers, where allowed by state regulations, for patients who are asymptomatic or experiencing mild, cold-like symptoms. 

If patients are experiencing severe symptoms such as a high-grade fever of 102 °F or more that has lasted for 48 hours or severe and constant shortness of breath, they will need to consult a healthcare provider and will not be eligible for testing at a Patient Service Center. 

Patients can schedule an appointment online. Appointments are strongly encouraged and walk-ins may be accommodated based on availability. 

Patients visiting a Patient Service Center must wear a mask per current CDC healthcare facility guidelines. 

What are the test names and test codes?

The test names in the Quest Test Directory for all IVD platforms for IgG and IgG/IgM antibody testing are as follows:

  • SARS-CoV-2 Antibody (IgG), Spike, Semi-Quantitative
  • SARS-CoV-2 Total Antibody, Spike, Semi-Quantitative
  • SARS-CoV-2 Antibody (IgG), Nucleocapsid, Qualitative
    (a component of the IgM/IgG panel, test code 31672)
  • SARS-CoV-2 Serology (COVID-19) Antibodies (IgG, IgM), Immunoassay

What are the SARS-CoV-2 serology antibody tests from Quest?

SARS-CoV-2 Antibody (IgG) Spike, Semi-Quantitative detects IgG antibodies in blood samples and provides a numerical result, with an index value of ≥1.00. Values above this index indicate immune response to recent or prior infection with SARS-CoV-2.

SARS-CoV-2 Total Antibody, Spike, Semi-Quantitative provides a single, combined numerical result with a level of 0.8 or more as a positive result, indicating a recent or prior infection with SARS-CoV-2.

SARS-CoV-2 Antibody (IgG) Nucleocapsid, Qualitative is a test used to detect IgG antibodies in serum (blood) samples. The test aids in identifying an immune response to recent or prior natural infection with SARS-CoV-2.

SARS-CoV-2 Serology (COVID-19) Antibodies (IgG, IgM), Immunoassay is a combined qualitative antibody (serum) panel that detects IgG and IgM antibodies to SARS-CoV-2. Separate results are provided for IgG and IgM.

IgG antibodies to SARS-CoV-2 are generally detectable in blood several days after initial infection, although the duration of time antibodies are present post-infection is not well characterized. Compared to IgG antibodies, IgM antibodies are typically detected earlier, during the acute phase of an infection but generally are not detected later in the infection. In the typical infection cycle, the presence of IgM would suggest a more recent or possibly unresolved infection, while the IgG antibody would suggest a prior infection.

The test systems that are used by Quest Diagnostics have been authorized by FDA under an EUA for use by authorized laboratories.1-6

Where can I find test-specific information?

All test-specific information can be found in the https://testdirectory.questdiagnostics.com/test/home.

Are Quest’s antibody test offerings for SARS-CoV-2 accurate?

SARS-CoV-2 Antibody (IgG), Spike, Semi-Quantitative (test code 34499)

  • Estimated assay sensitivity is >99.9%4,5 for specimens collected at least 15 days post–symptom onset,2 based on positive percent agreement (PPA)1 of SARS-CoV-2 IgG serology results among SARS-CoV-2 RNA−positive patients4,5
  • Estimated assay specificity is approximately 99.9%,4,5 based on negative percent agreement (NPA)2 assessed by performing cross-reactivity studies utilizing serum specimens positive for antibodies to other respiratory viruses pre– and post–COVID-19 time periods4,5

SARS-CoV-2 Antibody (IgG), Nucleocapsid, Qualitative (a component of the IgG/IgM panel) (test code 31672) (test code 39749)

  • Estimated assay sensitivity is >99.6% for specimens collected at least 15 days post–symptom onset,2 based on PPA1 of SARS-CoV-2 IgG serology results among SARS-CoV-2 RNA−positive patients2
  • Estimated assay specificity is >99.9%, based on NPA1 assessed by performing cross-reactivity studies utilizing serum specimens positive for antibodies to other respiratory viruses pre- and post-COVID-19 time periods2

SARS-CoV-2 Serology (COVID-19) Antibodies (IgG, IgM), Immunoassay (test code 31672)

  • Estimated assay sensitivity is 95% for specimens collected at least 15 days post–symptom onset,3 based on PPA1 of SARS-CoV-2 IgM serology results on patients who are SARS-CoV-2 RNA−positive3
  • Estimated specificity3 is >99% based on NPA1 assessed by performing SARS-CoV-2 IgM tests on serum specimens positive for antibodies to other respiratory viruses pre– and post–COVID-19 time periods3

The test systems that are used by Quest Diagnostics have been authorized by FDA under an EUA for use by authorized laboratories.1-6

The IgG and IgG/IgM antibody tests can help identify recent or prior infection to SARS-CoV-2 (which may be resolved or is still resolving), versus the molecular test which is used to help identify an active infection. The FDA authorized the intended use of these antibody tests to indicate whether a patient has had recent or prior COVID-19 infection. Citing concerns about test performance and validation, the FDA has now required all antibody tests to submit applications for EUA.

In addition to the robust validation performed by the manufacturers on each of the platforms, Quest verifies the performance characteristics of the assays using stringent acceptability criteria for precision, reproducibility, accuracy, method comparison, cross-reactivity, and clinical performance before starting patient testing.

Why is antibody testing important?

COVID-19 is a new infectious disease. Scientists are working to understand many things about it, such as how it spreads from person to person, why it affects people differently, how an individual’s immune system responds to the virus, and whether people can be infected more than once. To expand our knowledge and manage the spread of this virus, we need significant scientific advances—and antibody testing is a major part of those efforts, especially when used in conjunction with COVID-19 molecular testing. Antibody testing plays a critical role in the fight against COVID-19 and can aid in identifying individuals with an adaptive immune response to SARS-CoV-2 (COVID-19), indicating recent or prior infection.

Knowing the status of the population through antibody testing offers benefits globally, locally, and individually:

  • Helps public health officials determine prevalence of infection in the community
  • Provides guidance on the need for subsequent molecular testing for SARS-CoV-2 in surveillance programs (eg, IgG-positive individuals may not need ongoing surveillance after recovery from their primary infection)
  • Provides insight to help people understand whether they have been previously infected
  • The use of antibody testing may be particularly valuable to physicians treating individuals who are vulnerable and at higher risk of severe clinical outcomes from COVID-19 (eg, elderly individuals and those patients with COPD or cardiovascular risks)7
  • May be used in conjunction with other testing and a comprehensive protocol in return to work and society programs
  • Individuals whose blood contains antibodies may be eligible to serve as blood donors of convalescent plasma, which may provide an avenue for possible treatment for those who are seriously ill from COVID-198

When should an IgG or IgG/IgM serology test be performed?

Data suggest that IgM antibodies can be detected within a few days post-infection and IgG antibodies will be detectable from some individuals by 10 days after COVID-19 symptom onset.1-6

It is reasonable to conduct an antibody test after 14 days of being symptom-free because most people will develop a response in that timeframe. Further studies may further define and/or shorten the testing window.

What is the difference between molecular PCR testing and antibody testing for COVID-19?

The IgG and IgG/IgM antibody tests can help identify recent or prior infection to SARS-CoV-2 (which may be resolved or is still resolving), versus the molecular test which is used to help identify an active infection.

Has there been public guidance issued to healthcare providers on the clinical use of SARS-CoV-2 serology testing?

In a letter issued on June 19, 2020, the FDA recommended that healthcare providers continue to use serological tests intended to detect antibodies to SARS-CoV-2 to help identify people who may have been exposed to the SARS-CoV-2 virus or have recovered from the COVID-19 infection. In its guidance, the FDA referenced that experience with other viruses suggests that individuals whose blood contains IgG antibodies associated with SARS-CoV-2 infection—provided they are recovered and not currently infected with the virus—may be able to resume work and other daily activities in society. They may also be eligible to serve as potential donors of convalescent plasma to aid in the treatment of those infected with COVID-19.8

Who should be tested using the COVID-19 serology test?

The SARS-CoV-2 antibody tests are intended as aids in identifying individuals with an adaptive immune response to SARS-CoV-2 (COVID-19), indicating recent or prior infection and have not been validated for purposes of diagnosis of infection or disease (COVID-19) and cannot be used to rule in or rule out infection of COVID-19. Quest offers the molecular test (test code 39448) for diagnosing an active COVID-19 infection.

The FDA has authorized the intended use of these antibody tests to indicate whether a patient has had recent or prior COVID-19 infection.

Where can the SARS-CoV-2 serology specimens be collected?

Blood specimens for SARS-CoV-2 antibody testing can be collected by a hospital or health system or in any healthcare setting where a licensed phlebotomist can draw blood. Quest will be collecting serology specimens at Patient Service Centers (PSCs) by appointment across the country.

How will the Quest Diagnostics SARS-CoV-2 antibody test results be reported?

For IgG and IgG/IgM qualitative tests
There will be 3 results: positive, equivocal, and negative. Each result will carry a comment consistent with the FDA guidelines. Separate results will be provided for IgG and IgM antibodies.

For SARS-CoV-2 Antibody (IgG), Spike, Semi-Quantitative test
The semi-quantitative test detects IgG antibodies in blood samples and provides a numerical result.

  • A SARS-CoV-2 semi-quantitative IgG test result is interpreted as a positive value at an index4,5 of ≥1.00. This positive result means that an individual has developed an immune response to recent/prior SARS-CoV-2 infection within the limit of detection of the assay4,5,9,10
  • A negative semi-quantitative antibody result means that the patient serum specimen had no SARS-CoV-2 spike IgG antibodies, or that the relative level of antibodies in the patient specimen was below the index cutoff4,5

As the IgG and IgG/IgM tests are used to detect prior exposure to the virus, and not to diagnose active infection, these are not priority tests and providers will not be contacted to discuss results. Providers should obtain results via standard processes. Patients will be notified through the online MyQuest™ portal if they signed up for it.

What type of specimen is used for the SARS-CoV-2 serology test?

A serum sample obtained by taking a blood sample.

Should the SARS-CoV-2 antibody tests be submitted on their own requisitions?

SARS-CoV-2 antibody tests do not need to be on their own requisitions.

What is Quest’s capacity for the serology tests?

Quest is continuing to scale up testing capacity on the serology platform by expanding the test across its network of laboratories and adding other testing platforms.

How should SARS-CoV-2 antibody tests be interpreted?9-11

A positive IgG antibody test result suggests a potential immune response as a result of a prior or recent SARS-CoV-2 infection (which may be resolved or is still resolving). It usually takes at least 10 days after symptom onset for IgG detectable levels to be reached. Patients tested prior to this time may be negative for SARS-CoV-2 IgG antibodies. An IgG positive result may suggest an immune response to a primary infection with SARS-CoV-2, but the relationship between IgG positivity and immunity to SARS-CoV-2 has not yet been firmly established.

Compared to IgG antibodies, IgM antibodies are typically detected earlier, during the acute phase of an infection. In the typical infection cycle, the presence of IgM would suggest a more recent or possibly unresolved infection, while the IgG antibody would suggest a prior infection.

The use of an IgG/IgM panel can help identify and differentiate those individuals with a recent infection from those who have encountered SARS-CoV-2 and recovered, thus helping to further evaluate disease course.

Antibody tests have not been shown to definitively diagnose or exclude SARS-CoV-2 infection.

Presence of SARS-CoV-2 antibodies has been demonstrated in patients with undetectable viral RNA. Therefore, testing asymptomatic healthcare workers or patients with negative molecular diagnostic test results with antibody tests may add value in determining whether they have been exposed to SARS-CoV-2 or not.

What are the limitations of antibody testing?1-3

It is critical to confirm that the antibody testing being used is of highest quality and specificity. Furthermore, the FDA has provided specific performance threshold recommendations for specificity and sensitivity for all serology test developers.12 Antibody testing cannot stand on its own as the primary indicator of health status in response to COVID-19, but can be a valuable tool as part of a comprehensive response to the global pandemic.

It is not yet known how long antibodies persist following infection, if the presence of antibodies affords immunity, how long such immunity might last, and whether the presence of antibodies provides full protection from reinfection. Individuals may have detectable virus for several weeks following seroconversion. Per EEOC Guidelines, employers should not require antibody testing before allowing employees to re-enter the workplace.

References

  1. EUA authorized serology test performance. US Food and Drug Administration. Updated January 8, 2021. Accessed April 7, 2021. https://www.fda.gov/medical-devices/emergency-situations-medical-devices/eua-authorized-serology-test-performance
  2. Architect SARS-CoV-2 IgG (nucleocapsid). Package insert. Abbott Laboratories; 2020. Accessed April 7, 2021. https://www.fda.gov/media/137383/download
  3. Architect AdviseDx SARS-CoV-2 IgM (spike). Package insert. Abbott Laboratories; 2020. Accessed April 7, 2021. https://www.fda.gov/media/142940/download
  4. Atellica® IM SARS-CoV-2 IgG (COV2G; spike). Instructions for use. Siemens Healthcare Diagnostics Inc; 2020. Accessed April 7, 2021. https://www.fda.gov/media/140699/download
  5. ADVIA® Centaur® SARS-CoV-2 IgG (COV2G; spike). Instructions for use. Siemens Healthcare Diagnostics Inc; 2020. Accessed April 7, 2021. https://www.fda.gov/media/140704/download
  6. Cobas® Elecsys Anti-SARS-CoV-2 S (spike). Instructions for use. Roche Diagnostics Inc; 2021. Accessed April 7, 2021. https://www.fda.gov/media/144037/download
  7. CDC. Evidence used to update the list of underlying medical conditions that increase a person’s risk of severe illness from COVID-19. Updated March 29, 2021. Accessed May 5, 2021. https://www.cdc.gov/coronavirus/2019-ncov/need-extra-precautions/evidence-table.html
  8. FDA. Investigational COVID-19. Convalescent plasma. Guidance for industry. Issued February 11, 2021. Accessed May 5, 2021. https://www.fda.gov/media/136798/download
  9. FDA. Fact sheet for healthcare providers: Siemens Healthcare Diagnostics Inc Atellica® IM SARS-CoV-2 IgG (COV2G; spike). Updated July 31, 2020. Accessed April 7, 2021. https://www.fda.gov/media/140698/download
  10. FDA. Fact sheet for healthcare providers: Siemens Healthcare Diagnostics Inc ADVIA Centaur® SARS-CoV-2 IgG (COV2G; spike). Updated July 31, 2020. Accessed April 7, 2021. https://www.fda.gov/media/140702/download
  11. FDA. Fact sheet for healthcare providers: Ortho-Clinical Diagnostics, Inc. VITROS Immunodiagnostic products anti-SARS-CoV-2 IgG Reagent Pack. Updated February 12, 2021. Accessed February 22, 2021. https://www.fda.gov/media/137361/download
  12. FDA. Insight into FDA’s revised policy on antibody tests: prioritizing access and accuracy. Updated May 4, 2020. Accessed November 4, 2020. https://www.fda.gov/news-events/fda-voices/insight-fdas-revised-policy-antibody-tests-prioritizing-access-and-accuracy

Important information about SARS-CoV-2 (COVID-19) antibody testing

The IgG and IgM antibody tests are intended for use as an aid in identifying individuals with an adaptive immune response to SARS-CoV-2 (COVID-19), indicating recent or prior infection. Results are for the detection of SARS-CoV-2 antibodies.

IgG and IgM antibodies to SARS-CoV-2 are generally detectable in blood several days after initial infection, although the duration of time antibodies are present post-infection is not well characterized.

At this time, it is unknown for how long antibodies persist following infection and if the presence of antibodies confers protective immunity. Individuals may have detectable virus present for several weeks following seroconversion. Negative results do not preclude acute SARS-CoV-2 infection. If acute infection is suspected, molecular testing for SARS-CoV-2 is necessary. The tests should not be used to diagnose acute SARS-CoV-2 infection. False-positive results for the test may occur due to cross-reactivity from pre-existing antibodies or other possible causes.

The sensitivity of the test early after infection is unknown. Due to the risk of false-positive results, confirmation of positive results should be considered using a second, different IgM assay or an IgG assay. Samples should only be tested for IgM from individuals with 15 days to 30 days post–symptom onset. SARS-CoV-2 antibody negative samples collected 15 days or more post–symptom onset should be reflexed to a test that detects and reports SARS-CoV-2 IgG.

  • The antibody tests have not been FDA cleared or approved
  • The antibody tests have been authorized by FDA under an Emergency Use Authorization (EUA) for use by authorized laboratories
  • The antibody tests have been authorized only for detecting antibodies against SARS-CoV-2, not for any other viruses or pathogens
  • The SARS-CoV-2 Total Antibody, Spike, Semi-Quantitative test has been authorized by FDA under an EUA for use by laboratories certified under the Clinical Laboratory Improvement Amendments of 1988 (CLIA), 42 U.S.C. 263a, that meet requirements to perform high complexity tests
  • The IgM serology test component has been authorized only for the detection of IgM antibodies against SARS-CoV-2, not for any other viruses or pathogens
  • These tests are only authorized for the duration of the declaration that circumstances exist justifying the authorization of emergency use of in vitro diagnostic tests for detection and/or diagnosis of COVID-19 under Section 564(b)(1) of the Federal Food, Drug, and Cosmetic Act, 21 U.S.C § 360bbb-3(b)(1), unless the authorization is terminated or revoked sooner

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