Important COVID-19 Testing Information

Effective April 29, 2020, the Department of Pathology at Texas Children’s Hospital began offering a test for antibodies to SARS-CoV-2, the novel coronavirus which causes COVID-19. This test is designed to qualitatively detect total antibodies (IgM and IgG) to SARS-CoV-2. The test is performed on the automated Vitros platform and has received Emergency Use Authorization (EUA) from the FDA. At Texas Children’s, testing is available only as directed by a Texas Children’s provider and not open to the general public.

The preferred tests for diagnosis of acute COVID-19 infections are those that detect viral RNA. Antibody tests are not recommended for primary diagnosis of COVID-19, except in rare instances when patients present late, with a viral load that is below the detection limit of RT-PCR assays and when sampling of the lower respiratory tract is not possible.

Positive results (detection of SARS-CoV-2 antibodies) could suggest:

  1. A recent, past infection with SARS-CoV-2, regardless of whether the infection was symptomatic
  2. A current SARS-CoV-2 infection, several days after the first appearance of symptoms. Current studies suggest that the majority of individuals become antibody-positive approximately 7-14 days after onset of symptoms1.
  3. Infection with other Coronaviruses that cause the common cold

It is not known how long these antibodies persist, whether they confer immunity and if they confer immunity, how long such an immune state persists.

Negative results can help rule out a SARS-CoV-2 infection in the recent past. Negative results can also be associated with the first ~2 weeks of infection with SARS-CoV-2. FDA/CDC update of 4/7/20202

In addition to above, SARS-CoV-2 Antibodies (IgG/IgM) Testing3, 4 can also be used for identification of convalescent plasma donors and for epidemiologic studies of prevalence of infection in the community.

Specimen type: Serum or EDTA plasma (purple top tube, 1mL).

Turn-around Time: Samples that are received in the Medical Center Campus West Tower Laboratory will be resulted within 4 hours of receipt.

As more data emerge and guidelines on utility and testing of these antibodies improve, we will continue to update this information for our users.


FAQ: SARS-COV2 Antibodies (IgM + IgG), Qualitative [LAB1230223]

This serological assay qualitatively detects IgM and IgG antibodies against the spike (S) protein of SARS-CoV-2, the novel coronavirus which causes COVID-19. Results are reported as either “Reactive” or “Non-Reactive”. The test is performed on the automated Vitros platform and has Emergency Use Authorization (EUA) from the US FDA (1).

Should I use this test for diagnosis of COVID-19?
The preferred tests for diagnosis of acute COVID-19 infections are those that detect viral RNA. Antibody tests are not recommended for primary diagnosis of COVID-19, except in rare instances when patients present late in the disease course, with a viral load that is below the detection limit of RT-PCR assays or when sampling of the lower respiratory tract is not possible (2). When a patient presents 14 days post symptoms, the sensitivity and specificity of the test is greater than 98%

What does a positive result mean?
Positive results (detection of SARS-CoV-2 antibodies), when used in conjunction with the clinical picture, could suggest:

  1. A recent, past infection with SARS-CoV-2, regardless of whether the infection was symptomatic (4).
  2. An ongoingSARS-CoV-2 infection, several days after the first appearance of symptoms. Current studies suggest that the majority of individuals become antibody-positive approximately 14 days after onset of symptoms (5)(6)(7)(8). (In our validation, samples as early as 8 days after onset of symptoms show reactivity for antibodies).
  3. Past infection with other common cold coronaviruses (e.g. HKU1, NL63, OC43, 229E) due to potential cross-reactivity (In our validation, none of these samples tested have shown positivity for SARS-Cov-2 antibodies).

What does a negative result mean?
Negative results can help rule out a SARS-CoV-2 infection in the past several months. This is important for a patient who could not get a RNA test for the virus in the acute phase of their infection. Like other antibody tests, this may also produce a false negative result in immunocompromised patients.

How long do the antibodies persist?
It is not fully understood how long these antibodies persist. Initial studies of SARS-CoV-2 and experiences from the 2003 SARS-CoV epidemic indicate that IgG antibodies may last in patients’ blood for several months and up to 2 years (2)(4)(9).

Do antibodies confer immunity?
The Vitros SARS-CoV-2 antibody assay targets the viral S protein, the potential target of neutralizing antibodies (1). Our serological assays, and others that measure IgG and IgM levels, do not determine the neutralizing potential of antibodies, and whether these antibodies truly confer immunity. Whether patients who have had COVID-19, or who test positive for antibodies, can get re-infected after a period of time, is unclear at this point.

Should I order this test if I suspect multisystem inflammatory syndrome in children?
Some children with COVID-19 have developed a multisystem inflammatory disease associated with COVID (MIS-C) with features like Kawasaki Disease or similar illness. These children are older than the usual age of presentation for Kawasaki, but show the same symptoms. Both the RT-PCR and the antibody test for SARS-CoV-2 might help in the associated diagnosis of COVID-19. In many cases since it occurs 4-6 weeks after infection, the RNA test may be negative but the antibodies will most likely be positive.

What tubes should I use for specimen collection?
This test can be run on plasma (purple top EDTA) or serum, with a minimal volume of 1mL.

Can I add-on to another order?
If you have a serum/plasma specimen of sufficient volume in the lab that is less than 3 days old and has been refrigerated, you can add-on this test to the existing sample.

When is this test performed and how soon can I get the result?
This test is performed 24 hours a day, 7 days a week. Samples will be resulted within 4 hours of receipt in the Medical Center Campus West Tower Lab

What are the performance characteristics of this test?
The test has excellent precision with a coefficient of variation <10% and has performed with >99% concordance with other immunoassays for SARS CoV-2. The test has a positive and negative predictive value of 100% at a prevalence of 5% in the population.