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Quest Diagnostics

SARS-CoV-2 Antibody Testing

Test code(s) 39749, 31672, 34499, 39820

What’s new in this FAQ:

Question 8: How do I interpret a positive/reactive result on a semiquantitative SARS-CoV-2 spike IgG (TC34499) immunoassay? 

Question 17: Quest Diagnostics reports spike IgG semiquantitative current and previous values, when available. Why are my patient’s SARS-CoV-2 spike IgG semiquantitative values changing over time? 

The serology tests offered by Quest for detection of SARS-CoV-2 antibodies are summarized in Table 1.

Table showing Quest Diagnostics SARS-CoV-2 Serology Tests

Quest utilizes only SARS-CoV-2 antibody tests that have received emergency use authorization (EUA) from the US Food and Drug Administration (FDA). At this time, our SARS-CoV-2 antibody tests are laboratory-based, qualitative, and semiquantitative immunoassays; we do not offer rapid antibody tests.

At present, EUA SARS-CoV-2 antibody tests fall into 2 main groups: 

1.     Laboratory-based immunoassays: Several types of immunoassays are available in this category, such as enzyme-linked immunosorbent assays (ELISAs), chemiluminescent microparticle immunoassays (CMIAs), and immunometric assays.1 Within this laboratory-based test group, assays can be qualitative, semiquantitative, or quantitative and are generally performed using serum.1-3 These immunoassays use a solid phase coated with viral antigen to bind SARS-CoV-2 antibodies, but different tests may use different solid phases. For example, ELISAs use a plate and CMIAs use para-magnetic microparticles for detection.1 Quest currently offers high-complexity laboratory-based qualitative and semiquantitative immunoassays for SARS-CoV-2.

2.      Rapid serology/antibody tests: These are typically lateral flow assays that can be used for point-of-care (POC) testing. Rapid antibody tests most frequently test for SARS-CoV-2 IgG and/or IgM.1 These tests usually use blood specimens from a finger stick, and some can use saliva or other specimen types.1

Before patient specimen testing, Quest verifies the performance characteristics of the FDA emergency use authorized assays by completing CLIA/CAP-specified in-laboratory verification using stringent acceptability criteria for precision, reproducibility, accuracy, method comparison, cross-reactivity, and clinical performance. Highlights of the manufacturers’ clinical performance of the SARS-CoV-2 IgG and IgM kits used at Quest are as follows:  

1.     SARS-CoV-2 Antibody (IgG), Nucleocapsid, Qualitative (test code 39749; also a component of the IgM/IgG panel [test code 31672])

a.     Estimated assay sensitivity is >99.6% for specimens collected at least 15 days post–symptom onset,4 based on positive percent agreement (PPA)3 of SARS-CoV-2 IgG serology results among SARS-CoV-2 RNA−positive patients.4

b.     Estimated assay specificity4 is >99.9%, based on negative percent agreement (NPA)3 assessed by performing cross-reactivity studies utilizing serum specimens positive for antibodies to other respiratory viruses pre– and post–COVID-19 time periods.4

2.     SARS-CoV-2 Antibodies (IgG Nucleocapsid, IgM Spike), Qualitative (test code 31672)

a.     Estimated assay sensitivity is 95% for specimens collected at least 15 days post–symptom onset,5 based on PPA3 of SARS-CoV-2 IgM serology results among SARS-CoV-2 RNA–positive patients.5

b.     Estimated specificity5 is 99%, based on NPA3 assessed by performing SARS-CoV-2 IgM tests on serum specimens positive for antibodies to other respiratory viruses pre– and post–COVID-19 time periods.5

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

a.     Estimated assay sensitivity is >99.9% for specimens collected at least 15 days post–symptom onset,6,7 based on PPA3 of SARS-CoV-2 IgG serology results among SARS-CoV-2 RNA−positive patients.6,7

b.      Estimated assay specificity is approximately6,7 99.9%, based on NPA3 assessed by performing cross-reactivity studies utilizing serum specimens positive for antibodies to other respiratory viruses pre– and post–COVID-19 time periods.6,7

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

a.     Estimated assay sensitivity is >99.9% for specimens collected at least 15 days post–symptom onset,8 based on PPA3 of SARS-CoV-2 IgG serology results among SARS-CoV-2 RNA−positive patients.8

b.      Estimated assay specificity is approximately8 99.9%, based on NPA3 assessed by performing cross-reactivity studies utilizing serum specimens positive for antibodies to other respiratory viruses pre– and post–COVID-19 time periods.8

The antibody response to SARS-CoV-2 usually starts with IgM and/or IgA being detectable first, followed by the longer-lasting and more specific IgG.1 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.3-8 However, some people do not generate detectable IgG antibodies after infection, because of an underlying immune disorder, immunosuppression, or other, as yet unidentified, reasons.9,10

Additionally, an individual’s immune response can vary in the speed and strength of IgM and IgG production upon exposure to SARS-CoV-2, based on infective dose, viral burden, or host factors.9,10 In a review of current advances in SARS-CoV-2 serology testing, the combined use of IgM and IgG detection resulted in a higher sensitivity than that observed when detecting either antibody isotype alone.9,10

No. At present, no antibody tests have an FDA EUA specified intended use that includes definitive diagnosis of, or ruling out of, current SARS-CoV-2 infection.2-9 Serologic IgM and IgG assays provide information about whether a person has developed an immune response to a COVID-19 infection.1,3-8 A molecular diagnostic RNA assay should be considered to help diagnose a current infection.1,3-8 Although the FDA has not specified the intended use of antibody tests to diagnose SARS-CoV-2 infection, serologic assays may be used to support clinical assessment of

  • Persons who present to clinicians late in their illness (9-14 days after symptom onset), when used in conjunction with viral detection tests1
  • Persons suspected to have a post-infectious syndrome caused by SARS-CoV-2 infection: (eg, multisystem inflammatory syndrome in children [MIS-C])1

The CDC guidance for SARS-CoV-2 serology testing is summarized in the table below and can be found here.

Table 2: Interpretation of Anti-S and Anti-N Antibody Results Based on Vaccination Status

 

The clinical significance of an immune response after vaccination is not yet known.1,11-13 At this time, there are no FDA emergency use authorized tests for individuals who have received a COVID-19 vaccination, and the performance characteristics of the authorized antibody tests have not been established for those individuals.3 Similarly, the CDC states, “Antibody testing is not currently recommended to assess immunity to COVID-19 following COVID-19 vaccination or to assess the need for vaccination in an unvaccinated person.”1

A nucleocapsid SARS-CoV-2 IgG test would not be expected to detect an immune response in individuals who have received COVID-19 spike vaccination (and who had not been infected naturally).

The IgG response is usually slower in people who are either taking immunosuppressive therapies or immunocompromised because of a health condition.4,11 Given the variability in timing of an IgG response, a repeat serology IgG test should be considered after an additional 2- to -3-week period for individuals who are initially antibody negative and are thought to have clinically recovered from a SARS-CoV-2 infection.4,11

In populations with a high prevalence of infection with non–SARS-CoV-2 coronavirus strains, a positive result could also be due to past or present infection with one of these strains. For more information on CDC common coronavirus surveillance information, refer to CDC.gov/Surveillance/NREVSS/Coronavirus/Index.html.

Quest only offers SARS-CoV-2 IgM (spike) in a panel that includes a separate IgG (nucleocapsid) determination.4,5 The results from this qualitative test for SARS-CoV-2 IgM can be positive (reactive) or negative (non-reactive).5,14,17

A positive (reactive) result indicates that antibodies to SARS-CoV-2 were detected, and the individual has potentially been infected with SARS-CoV-2.1,3,5,14 SARS-CoV-2 IgM is generally detectable in blood several days after initial infection. Detection of IgM may indicate a recent infection.1,5,12-16 A spike SARS-CoV-2 IgM test may detect an immune response in individuals who have received a COVID-19 vaccination (and who have not been infected naturally). However, the clinical significance of such a result is unknown, in part because the performance characteristics of this test in these individuals have not been established.

It is unknown how long SARS-CoV-2 IgM remains detectable post-infection.1,3,5,14

Whether SARS-CoV-2 antibodies confer immunity to infection also remains unknown.1,3,5,14 Incorrect assumptions of immunity may lead to premature discontinuation of physical distancing requirements and could increase the risk of infection for individuals, their household members, and the public.1

A negative test result means that SARS-CoV-2 IgM was not present in the specimen at levels above the limit of detection.1,5,14 However, patients tested early after infection may not have detectable antibodies despite active infection.1,5,14 A negative result should not be used to rule out infection. Testing of patient specimens for the presence of virus material (eg, RNA or antigen) should be performed if acute infection is suspected.1,3,5,11 

A recent publication supports the use of simultaneous IgG/IgM measurements (regardless of method) to significantly improve assay sensitivity.9,10 Regardless of the test result, individuals should continue to follow CDC guidelines to reduce the risk of infection, including social distancing and wearing masks.1

A SARS-CoV-2 semiquantitative IgG test result is interpretated as positive at an index value of ≥1.00. The analytical measurement interval (reporting range) is 0.50 to 150.0 for the Siemens Atellica assay and 0.5 to 100 for the Siemens Centaur assay.6,7 A positive result means that an individual has developed an immune (IgG) response to recent/prior SARS-CoV-2 infection that is above the cutoff of the assay (1.00).6,7,16,17 Positive results may also occur after a COVID-19 vaccination, but the clinical significance of this finding is not yet fully understood.1,11-13 There are currently no FDA emergency use-authorized tests for individuals who have received a COVID-19 vaccination, and the performance characteristics of the current antibody tests have not been established for these individuals. Since much is still not known about the body’s immune response to this virus, this test result cannot be used to indicate a level of immunity/protection or rule out the chance for reinfection.1,5,15

This test should not be used to diagnose current SARS-CoV-2 infection.1,5,15 If a current infection is suspected, direct molecular or antigen testing for SARS-CoV-2 is necessary.1,3,5-7,16,17         

Index values reported as ˂1.00 are interpretated as negative. A negative semiquantitative antibody result means that the patient serum specimen has no SARS-CoV-2 spike IgG antibodies, or that the relative level of antibodies in the patient specimen is below the index cutoff.6,7

Note 1: The index value should not be interpreted as a measurement of durable immunity or protection from SARS-CoV-2 infection or reinfection.1,3,6,7 Durability and duration of immunity to SARS-CoV-2 are still not clearly defined and continue to be an area of national and global scientific and public health research.1,3 Results obtained with this assay may not be used interchangeably with values obtained with different manufacturers' test methods.1

Note 2: Tests performed after November 8, 2021, utilize an updated version of the SARS-COV-2 AB (IGG) SPIKE, SEMI QN assay (anti-S1 RBD,IgG assay [sCOVG]). Test results generated after this date are not equivalent to those generated on or before this date. The index value of the new assay’s calibration to the WHO 20/136 Standard in binding antibody units (BAU/mL) may be found in this reference: Freeman J, Conklin J. Standardization of two SARS-CoV-2 serology assays to the WHO 20/136 human standard reference material. J Virol Methods. 2022;300:114430. doi:10.1016/j.jviromet.2021.114430

The result of the SARS-CoV-2 Total Antibody, Spike, Semi-Quantitative immunoassay test is reported as positive at an index of (analytic measurement interval of 0.4-2500.0 U/mL).8 A positive result means that an individual has developed an immune response to a recent or past infection by SARS-CoV-2.8,15  Positive results may also occur after a COVID-19 vaccination, but the clinical significance is not yet known.1,11-13 At this time, there are no FDA emergency use-authorized tests for individuals who have received a COVID-19 vaccination; the performance characteristics of authorized antibody tests have not been established for individuals who have received a COVID-19 vaccination. Because much is still not known about the body’s immune response to this virus, this test result cannot be used to indicate the level of immunity or rule out the chance of reinfection.8,15 This test should not be used to diagnose current SARS-CoV-2 infection. If a current infection is suspected, direct molecular or antigen testing for SARS-CoV-2 is necessary.8,15

Conversely, a negative result is reported at an index of ˂0.8 U/mL.8 A negative semiquantitative antibody result means that the patient serum specimen had no detectable level of SARS-CoV-2 spike IgG antibodies, or that the relative level of antibodies in the patient specimen was below the index cutoff.8,15

Note: The index value should not be interpreted as a measurement of durable immunity or protection from SARS-CoV-2 infection or reinfection.1,3,8 Durability and duration of immunity to SARS-CoV-2 are still not clearly defined and continue to be areas of national and global scientific and public health research.1,3 Results obtained with this assay may not be used interchangeably with values obtained with different manufacturers' test methods.

The presence of IgG and/or IgM antibody to SARS-CoV-2 indicates that the patient has developed an immune response to the SARS-CoV-2 virus. The presence of IgG and/or IgM antibody to SARS-CoV-2 could also indicate potential immune response to a spike vaccine.1,3-5 The clinical significance of a positive antibody result for individuals who have received a COVID-19 vaccine is unknown. The performance of this test has not been established in the context of COVID-19 vaccines. Although the immune response may protect against reinfection, this has yet to be conclusively established.1,3,14,18,19 It is not known how long antibodies to the virus will protect someone, if at all. Cases of reinfection with SARS-CoV-2 (COVID-19) have occasionally been reported.1,3,14,18,19

The tests in this panel are intended for qualitative detection of IgG and IgM antibodies to SARS-CoV-2 in human serum and plasma (lithium heparin). The 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.4,5 At this time, it is unknown for how long antibodies persist following infection and if the presence of antibodies confers protective immunity.1 The test should not be used to diagnose or exclude acute SARS-CoV-2 infection.1 Results are for the detection of SARS-CoV-2 IgG and IgM antibodies. IgG and IgM antibodies to SARS-CoV-2 are generally detectable in blood several days after initial infection, although the duration that antibodies are present post-infection is not well characterized. Individuals may have detectable virus present for several weeks following seroconversion.

Positive spike protein antibody results may also occur after a COVID-19 vaccination, but the clinical significance is not yet known.1,11,12,14 At this time, there are no FDA emergency use authorized tests for individuals who have received a COVID-19 vaccination, and the performance characteristics of the authorized antibody tests have not been established for those individuals. Clinical researchers continue to investigate what constitutes SARS-CoV-2 protective immunity and long-term vaccine efficacy.11,13,15 This is an area of active clinical research. The CDC states, “Antibody testing is not currently recommended to assess for immunity to COVID-19 following COVID-19 vaccination or to assess the need for vaccination in an unvaccinated person.”1

Manufacturers’ validation of SARS-CoV-2 IgG assays utilized by Quest reported less than 1% positivity in specimens from pre-COVID times4,6,7 (2010, 2017, and 2019).

In an antibody cross-reactivity study of 143 specimens from 30 different categories of infectious disease and autoimmune disease, only 1 specimen (with rheumatoid factor) had a SARS-CoV-2 IgM-positive result.5 In a medical condition cross-reactivity study using 65 specimens from 13 different categories, only 1 specimen (from a hemodialysis patient) tested positive for SARS-CoV-2 IgM.5

The cross-reactivity of the Quest SARS-CoV-2 IgG and SARS-CoV-2 IgM immunoassays (CMIAs)4,6-7 is <1%.

Neutralization assays are performed to help assess the ability of neutralizing antibodies (NAbs) in patient serum to neutralize virus infectivity in vitro.18 These tests are potentially useful to assess whether past infection (or potential vaccination) has provided protection against infection. The clinical significance of a positive NAb result for individuals who have received a COVID-19 vaccine is unknown. In these tests, serial dilutions of patient serum are incubated with known infectious virus concentrations and then added to virus-susceptible cell lines.18 After incubation, infected cells are quantified to determine the effectiveness of patient antibodies in neutralizing the virus.19,20 The presence of NAbs may suggest in vivo immunity to viral infection. Convalescent sera with NAbs are being studied as a treatment for severe COVID-19.18,19 Testing for NAbs is only available at some specially equipped public health laboratories and research facilities. SARS-CoV-2 NAb testing is not performed at Quest. 

No, a positive result does not have implications for vaccination. At this time, the CDC and ACIP guidance states that previous SARS-CoV-2 infection, whether symptomatic or asymptomatic, is not considered a contraindication to vaccination, and that serologic testing for SARS-CoV-2 antibodies is not recommended prior to vaccination.1,21

No, semiquantitative tests can vary significantly, both in the range of detection and, more importantly, in the unit of measure. Not all assays use the same index cutoff for positive and negative; some assays use U/mL and others provide no unit of measure for the reported semiquantitative index value. Therefore, SARS-CoV-2 semiquantitative antibody values may not be used interchangeably with values obtained from different manufacturers' test methods. As evidenced in the FDA expanded authorization of semiquantitative tests that may be used in the determination of high-titer COVID-19 convalescent plasma (CCP) donors, qualifying results of different test methods are expressed with different units and measurements.22

A semiquantitative index value should not be interpreted as a measurement of durable immunity or protection from SARS-CoV-2 infection or reinfection.1,3,8

Most persons with SARS-CoV-2 infection develop virus-specific antibodies within several weeks, but antibody levels may change (usually decline) over time.23 Individual factors likely play an important role in the observed antibody level in a particular individual at a particular time point. Understanding the timeline of antibody decline following infection may be important for interpreting SARS-CoV-2 serology results.

One study24 found that individuals who had an asymptomatic SARS-CoV-2 infection, compared to those who had symptomatic illness, had lower initial antibody levels during the acute phase following infection and later during the convalescent phase. The proportion of individuals who remained antibody-positive was also lower.

Similarly, another study23 demonstrated that participants with higher initial antibody responses post-infection were more likely to remain antibody-positive at follow-up compared to those with lower initial antibody responses. Individuals receiving SARS-CoV-2 vaccines usually demonstrate a rise in spike protein antibody levels post-vaccination, which then decline over time.25

References

  1. Interim guidelines for COVID-19 antibody testing. Centers for Disease Control and Prevention. Updated January 24, 2022. Accessed July 20, 2022. https://www.cdc.gov/coronavirus/2019-ncov/lab/resources/antibody-tests-guidelines.html#anchor_1590280017822
  2. FAQs on testing for SARS CoV-2. US Food and Drug Administration. Updated January 22, 2022. Accessed April 19, 2021. https://www.fda.gov/medical-devices/coronavirus-covid-19-and-medical-devices/faqs-testing-sars-cov-2
  3. EUA Authorized Serology Test Performance. US Food and Drug Administration. Updated December 3, 2021. Accessed July 20, 2022. https://www.fda.gov/medical-devices/emergency-situations-medical-devices/eua-authorized-serology-test-performance
  4. Architect SARS-CoV-2 IgG (nucleocapsid). Package insert. Abbott Laboratories; 2022. Accessed July 20, 2022. https://www.fda.gov/media/137383/download
  5. Architect AdviseDx SARS-CoV-2 IgM (spike). Package insert. Abbott Laboratories; 2021. Accessed July 20, 2022. https://www.fda.gov/media/142940/download
  6. Atellica® IM SARS-CoV-2 IgG (COV2G; spike). Instructions for use. Siemens Healthcare Diagnostics Inc; 2022. Accessed July 20, 2022. https://www.fda.gov/media/146931/download
  7. ADVIA Centaur® SARS-CoV-2 IgG (COV2G; spike). Instructions for use. Siemens Healthcare Diagnostics Inc; 2021. Accessed July 20, 2022. https://www.fda.gov/media/150238/download
  8. Cobas® Elecsys Anti-SARS-CoV-2 S (spike). Instructions for use. Roche Diagnostics Inc; 2022. Accessed July 20, 2022. https://www.fda.gov/media/144037/download
  9. 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
  10. Li Z, Yi Y, Luo X, et al. Development and clinical application of a rapid IgM‐IgG combined antibody test for SARS‐CoV‐2 infection diagnosis. J Med Virol. 2020;92(9):1518-1524. doi:10.1002/jmv.25727
  11. Livingston EH, Malani PN, Creech CB. The Johnson & Johnson vaccine for COVID-19. JAMA. 2021;325(15):1575. doi:10.1001/jama.2021.2927
  12. Polack FP, Thomas SJ, Kitchin N, et al. Safety and efficacy of the BNT162b2 mRNA Covid-19 vaccine. N Eng J Med. 2020;383(27):2603-2615. doi:10.1056/NEJMoa2034577
  13. Baden LR, El Sahly HM, Essink B, et al. Efficacy and safety of the mRNA-1273 SARS-CoV-2 vaccine. N Eng J Med. 2021;384(5):403-416. doi:10.1056/NEJMoa2035389
  14. Fact sheet for healthcare providers: Abbott Laboratories AdviseDx SARS-CoV-2 IgM (spike). US Food and Drug Administration. Updated September 2, 2021. Accessed July 20, 2022. https://www.fda.gov/media/142938/download
  15. Fact sheet for healthcare providers: Abbott Laboratories Inc SARS-CoV-2 IgG. US Food and Drug Administration. Updated May 24, 2022. Accessed July 22, 2022. https://www.fda.gov/media/137381/download
  16. Fact sheet for healthcare providers: Siemens Healthcare Diagnostics Inc Atellica® IM SARS-CoV-2 IgG (COV2G; spike). US Food and Drug Administration. Updated Sept. 21, 2021. Accessed July 22, 2022. https://www.fda.gov/media/146929/download
  17. Fact sheet for healthcare providers: Siemens Healthcare Diagnostics Inc ADVIA Centaur® SARS-CoV-2 IgG (COV2G; spike). US Food and Drug Administration. Updated Aug. 10, 2021. Accessed July 22, 2022.  https://www.fda.gov/media/150236/download
  18. Reinfections and COVID-19. Centers for Disease Control and Prevention. Updated January 20, 2022. Accessed July 20, 2022. https://www.cdc.gov/coronavirus/2019-ncov/your-health/reinfection.html
  19. 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
  20. Mo H, Zeng G, Ren X, et al. Longitudinal profile of antibodies against SARS-coronavirus in SARS patients and their clinical significance. Respirology. 2006;11(1):49-53. doi:10.1111/j.1440-1843.2006.00783.x
  21. Interim considerations for COVID-19 vaccination of healthcare personnel and long-term care facility residents. Centers for Disease Control and Prevention. Reviewed August 23, 2021. Accessed July 20, 2022. https://www.cdc.gov/vaccines/hcp/acip-recs/vacc-specific/covid-19/clinical-considerations.html
  22. Convalescent plasma EUA letter of authorization. US Food and Drug Administration. Updated February 14, 2022. Accessed July 20, 2022. https://www.fda.gov/media/141477/download
  23. Self WH, Tenforde MW, Stubblefield WB, et al.  Decline in SARS-CoV-2 antibodies after mild infection among frontline health care personnel in a multistate hospital network—12 States, April-August 2020. MMWR Morb Mortal Wkly Rep. 2020;69(47):1762-1766. doi:10.15585/mmwr.mm6947a2
  24. Long QX, Tang XJ, Shi QL, et al. Clinical and immunological assessment of asymptomatic SARS-CoV-2 infections. Nat Med. 2020;26(8):1200-1204. doi:10.1038/s41591-020-0965-6
  25. Herzberg J, Vollmer T, Fischer B, et al. SARS-CoV-2-antibody response in health care workers after vaccination or natural infection in a longitudinal observational study. Vaccine. 2022;40(2):206-212. doi:10.1016/j.vaccine.2021.11.081

 

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 SARSCoV-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 IgM 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 EUA for use by authorized laboratories;
  • The antibody tests have been authorized only for the detection of IgG antibodies against SARS-CoV-2, not for any other viruses or pathogens; and,
  • The antibody tests are only authorized for the duration of the declaration that circumstances exist justifying the authorization of emergency use of in vitro diagnostics for detection and/or diagnosis of COVID-19 under Section 564(b)(1) of the Act, 21 U.S.C. § 360bbb-3(b)(1), unless the authorization is terminated or revoked sooner.

 

This FAQ is provided for informational purposes only and is not intended as medical advice. Test selection and interpretation, diagnosis, and patient management decisions should be based on the physician’s education, clinical expertise, and assessment of the patient.



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