COVID-19 Antibody Testing

An antibody (also known as an immunoglobulin) is part of our body’s response to a foreign molecule or pathogen (also known as an antigen) such as a virus or bacterium. The immune response is valuable as it helps to fight off infection. Protective antibodies can in some cases provide long-term immunity, so we do not become re-infected with the same viruses or bacteria. As such, antibodies are vital for our health.

Yet, we don’t always develop antibodies—or the right or sufficient antibodies—to fight off all infectious diseases. For example, people infected with HIV or hepatitis C virus do not usually develop protective antibodies.

Yes, there are five primary classes of antibodies. Of those, IgG, IgM, and IgA are often used as part of infectious disease serology testing.

• IgG antibodies are found in all body fluids. They account for 75 to 80 percent of all antibodies. IgG antibodies are very important in fighting bacterial and viral infections and when present indicate that someone has previously been exposed to a particular antigen and has developed an immune response. In general, these antibodies usually appear 10-14 days after symptom onset.
  
  
• IgM antibodies are found in blood and lymph fluid and are the first type of antibody made in response to an infection, usually detectable within 3-7 days from the start of the infection.
  
  
• IgA antibodies play a crucial role in the immune function of mucous membranes, such as the respiratory epithelium, but is also found in the blood. These antibodies also appear early in the infection process (3-7 days).

Molecular PCR tests are used to directly detect the presence of the virus, rather than the presence of the body’s immune response, or antibodies. By detecting viral RNA, which will be present in the body before antibodies form, the molecular PCR tests can tell whether someone has the virus very early on and whether they are infectious. An antibody test tells us what proportion of the population has been infected. It won’t tell you who is infected, because the antibodies are generated after a week or two, after which time the virus should have been cleared from the system. But it tells you who has been infected and who is likely to be immune to the virus.

Antibody testing provides insight into an individual’s immune response after exposure to the SARS-CoV-2 virus but is not intended to diagnose an active infection. For those vaccinated, the measurement of IgG levels can be used to assess whether an individual has mounted an immune response to the COVID-19 vaccine. Although this test is designed to provide information on one’s immune response, studies are still needed to determine the level that indicates protective immunity as well as how long the immune response may last.

According to a recent white paper summary issued by the American Clinical Laboratory Association (ACLA), when used appropriately, antibody testing may help determine the number of individuals who have been infected with SARS-CoV-2. By supporting screening for individuals using serology, healthcare professionals can provide a more detailed assessment regarding the true rate of infection and gain a better understanding of the case fatality rate to help inform public health strategies. Serologic testing can also be used to support contact tracing (the process of identifying persons who may have come into contact with an infected person and subsequent collection of further information about these contacts) to stop the spread of the infection in the community.

There are three types of antibodies that can be measured: IgA, IgM, and IgG. Some assays measure all three antibodies (IgA, IgM, and IgG) at one time, and is referred to as a Total Antibody Test.

It takes time to develop an immune response with development of antibodies. Generally, most people form antibodies except those who are either immunocompromised or IgG deficient. Testing too soon will lead to a negative antibody test result. There is insufficient scientific information to understand the variation of timing and amount of antibody that develops to the SARS-CoV-2 virus that can be applied to all patients. Yet, we have experience with other viruses and can apply these learnings to SARS-CoV-2 until we know more.

Studies have begun measuring the seroconversion in SARS-CoV-2 patients. In one such study, 173 hospitalized patients in China, all patients (100%) developed antibodies against SARS-CoV-2.1 The median time to have detectable antibodies (called seroconversion) was 11 to 14 days, depending upon the type of immunoglobulin. (The median time is the number of days when 50% of those tested positive after onset of symptoms.) 94% and 80% demonstrated seroconversion with IgM and IgG, respectively, by day 15 after onset of symptoms. This study provides information from a small number of patients; larger studies are needed.

SARS-CoV-2 antibody tests are designed to detect specific antibodies against this virus. A positive IgG antibody test result suggests past exposure and may indicate prior infection which may be resolved or is still resolving, and/or protection against re-infection (“protective immunity”).

A diagnosis, in general, is to rule in or to rule out the presence of a medical condition. Again, the SARS-CoV-2 antibody test cannot be used to rule in or rule out active COVID-19 infection.

To date, the United States Food and Drug Administration (FDA) has not required review of information about any specific antibody test. The FDA is allowing laboratories to perform these tests without extensive review in response to the COVID-19 pandemic emergency.

This test has been authorized by the FDA under Emergency Use Authorization (EUA) for use by authorized laboratories such as Sonora Quest. View FDA Authorized Labeling 

A positive IgG antibody test result suggests recent or prior infection with SARS-CoV-2. 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 or to a COVID-19 vaccination, but the relationship between IgG positivity and immunity to SARS-CoV-2 has not yet been firmly established. At this time, a positive IgG result has not been shown to indicate immunity or prevent transmission of COVID-19, as such social distancing, also called “physical distancing,” should still be followed to assure that we continue to protect ourselves, our family, and our community.

A positive IgM and/or IgA test result, with a positive/negative IgG result, may indicate an active COVID-19 infection. A negative IgM and/or IgA antibody test result is likely to indicate that: (1) the person has not been infected with SARS-CoV-2 or (2) the person has been infected but there has not been enough time to produce an IgM and/or IgA response. 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

If you have IgG antibodies and you have symptoms, you likely have an active infection, you may infect others, and you may need to seek medical attention.

While there is a lot of uncertainty with this new virus, it is also possible that, over time, broad use of antibody tests and clinical follow-up will provide the medical community with more information about how safely someone who has recovered from the virus can be exposed to it again.

We are defining “symptomatic” per CDC guidelines3: including (1) fever, measured as temperature > 100.3 °F, or subjective fever based on clinical judgment; and (2) respiratory symptoms, including cough, shortness of breath, congestion or runny nose, sore throat and/or other symptoms such as fatigue, muscle or body aches, new loss of taste or smell, nausea or vomiting, and diarrhea. Medical evaluation may be recommended for lower temperatures or other symptoms based on assessment by public health authorities.

The ADVIA Centaur® SARS-CoV-2 IgG (sCOVG) assay received Emergency Use Authorization (EUA) from the US Food and Drug Administration (FDA) to detect IgG antibodies against SARS-CoV-2. For additional information see -

Information for Healthcare Providers

We perform our own validation using stringent acceptability criteria which consists of precision, reproducibility, accuracy, method comparison, cross reactivity, and clinical performance before starting patient testing.

The accuracy of Sonora Quest’s SARS-CoV-2 serology testing performance characteristics are on par with other common virology antibody tests routinely performed at Sonora Quest (e.g., Measles, Mumps, Rubella).

In order to maximize our capacity and flexibility for testing in this time of need, Sonora Quest is utilizing the ADVIA Centaur SARS-CoV-2 IgG (COV2G) assay developed by Siemens Healthcare Diagnostic to perform antibody testing for COVID-19. This assay provides a semi-quantitative test result to the SARS-CoV-2 S1 RBD (receptor binding domain) of the spike protein.

The clinical applicability of a semi-quantitative result is currently unknown and should not be interpreted as an indication or degree of immunity, protection from reinfection, or compared to other SARS-CoV-2 antibody assays.

The serological IgG assay that Sonora Quest offers is validated to be highly specific for SARS-CoV-2. For this validated assay, a positive result indicates a high likelihood of a prior infection and that a person has mounted an immune response. Different assays target different viral proteins. Some assays detect antibodies to the nucleocapsid and others detect antibodies to the spike protein. Spike and nucleocapsid assays are highly correlated with each other.

Someone who has undergone a natural SARS-CoV-2 infection should have antibodies to both the nucleocapsid and spike proteins, while a vaccinated individual with no previous exposure to SARS-CoV-2 should only have antibodies to the spike protein.

The test will provide a qualitative result (i.e., reactive or nonreactive) and a numerical value. An index value ≥1.00 is considered reactive. The clinical applicability of a semi-quantitative result is currently unknown and should not be interpreted as an indication or degree of immunity, protection from reinfection, or compared to other SARS-CoV-2 antibody assays This test is not a Priority test and providers will not be contacted to discuss results. Providers should obtain results via standard processes. Patients can access their results through our patient results portal at SonoraQuest.com.

A reactive result indicates exposure to SARS-CoV-2 and may indicate resolved infection or an immune response a COVID-19 vaccine. COVID-19 science on the role of COVID-19 antibody testing in assessing potential immunity is evolving. We encourage individuals, with their providers, to carefully consider results of these tests in connection with other factors, including symptoms and history.

This suggests a person has not been exposed to SARS-CoV-2 or has been exposed very recently (antibodies have not yet been produced) or has possibly not mounted a measurable immune response to a COVID-19 vaccine. COVID-19 science on the role of COVID-19 antibody testing in assessing potential immunity is evolving. We encourage individuals, with their providers, to carefully consider results of these tests in connection with other factors, including symptoms and history.

The performance of this test was established based on the evaluation of a limited number of clinical specimens. The clinical performance has not been established in all circulating variants but is anticipated to be reflective of the prevalent variants in circulation at the time and location of the clinical evaluation. Performance at the time of testing may vary depending on the variants circulating, including newly emerging strains of SARS-CoV-2 and their prevalence, which change over time.

The presence of IgG indicates prior exposure to SARS-CoV-2 and/or an immune response to a COVID-19 vaccine. At this time, an index value that correlates with protective immunity has not been established nor the duration of one’s immunity either by natural infection or vaccination. However, in previous viral outbreaks of SARS (SARS-CoV), IgG has been shown to provide immunity for up to 2 years. In most other viral diseases, IgG responses measurable by serological testing positively correlate with some level of protective immunity. An animal study of SARS-CoV-2 demonstrated protective immunity after infection. Early human studies demonstrate development of protective / neutralizing antibody responses in individuals infected with SARS-CoV-2.

Our position at Sonora Quest is that antibody testing is an important tool in assessing potential risk and fostering a safer environment for all of us. We look forward to additional science to establish clearly the role of antibody testing in inferring immunity for COVID-19. Other respiratory illnesses, including SARS, a cousin coronavirus of COVID-19, has been shown to produce antibodies that can be assessed via lab testing to infer immune protection for a period of time. We encourage all individuals, regardless of their antibody response/test result, to continue to practice safety and health measures, such as social distancing, to further minimize risk.

Yes. In a letter issued on April 17, 2020, the US Food and Drug Administration (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.

The test name for IgG antibody testing is SARS-CoV-2 Antibody (IgG), Spike, Semi-Quantitative. The test code is 907097.

The SARS-CoV-2 Antibody (IgG), Spike, Semi-Quantitative test is a semi-quantitative test that detects IgG antibodies to the spike protein of the SARS-CoV-2 virus in your blood. The test code 907097 includes testing for the IgG antibody only.

SARS-CoV-2 antibody tests are designed to detect specific antibodies against this virus. A positive IgG antibody test suggests exposure to the SARS-CoV-2 virus and/or the development of an immune response to a COVID-19 vaccine.

The SARS-CoV-2 antibody test has not been validated for purposes of diagnosis of infection or disease (COVID-19) and cannot be used to rule in or rule out infection or COVID-19. Sonora Quest offers the molecular test (test code 907080 for swab samples and 907078 for lower respiratory samples) for diagnosing an active COVID-19 infection.

It usually takes at least 10 days after symptom onset for IgG to reach detectable levels. Based on a recent study of 173 hospitalized patients in China,1 all patients (100%) developed antibodies against SARS-CoV-2. The median time to have detectable (IgG) antibodies (called seroconversion) was 11 to 14 days.

For those vaccinated, the evaluation of an immune response would be most beneficial at least 10 days after the completion of the vaccine regimen (the timeframe is based on vaccine efficacy studies and the antibody response seen in a natural infection). Although this test is designed to assess the level of an individual’s immune response, studies are still needed to determine the level that indicates protective immunity as well as how long the immune response may last.

A serum sample obtained by taking a blood sample.

The required volume is 1.0 mL (0.5 mL minimum) of serum.

The supplies needed are serum separator vacutainer tubes (SSTs).

Specimen stability for the antibody test is as follows:

• Room temperature: 24 hours
  
  
• Refrigerated (2 °C–8 °C): 7 days
  
  
• Frozen (-20 °C): 30 days

Specimens should be transported refrigerated to Sonora Quest according to standard operating procedures. Cold packs/pouches must be used if placing specimens in a lockbox for courier pick-up. STAT pick-up cannot be ordered for this test. The COVID-19 antibody test does not need to be ordered on its own separate requisition.

COVID-19 antibody testing has a published turnaround time within 1 – 3 days. Currently, the majority of tests are being reported within 2 days. Testing turnaround time may vary based on testing demand, supplies, and other factors.

Sonora Quest initially expects to be able to run 900 tests per day and is continuing to scale up testing capacity on the antibody platform.

IgG antibody testing (test code 907097) can be ordered to assess one’s immune response to a SARS-CoV-2 infection or to a COVID-19 vaccine. IgG antibody testing should not be used to diagnose an active infection, and symptomatic patients should always be diagnosed using a molecular COVID-19 test (test code 907080 for swab samples and 907078 for lower respiratory samples).

The CPT code for the testing is 86769. CPT codes are based on American Medical Association (AMA) guidelines and are for informational purposes only. CPT coding is the sole responsibility of the billing party. Please direct any questions regarding coding to the payer being billed.

No. Only the molecular test (test code 907080 for swab samples and 907078 for lower respiratory samples) should be used to test a symptomatic patient for COVID-19. The IgG antibody test will help to identify people who have been exposed to the SARS-CoV-2 virus and may indicate prior infection which may be resolved or is still resolving, and/or protection against re-infection (“protective immunity”).

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. Sonora Quest will be collecting serology specimens at select Patient Service Centers (PSCs) across Arizona. These locations are posted on SonoraQuest.com/coronavirus and are updated on SonoraQuest.com for appointment scheduling. See list of Patient Service Centers available for scheduling.

The price of the test is $65 if billed directly to a healthcare provider’s office, and $75 if billed to insurance or if a patient decides to purchase the test themselves without a doctor’s order or insurance through our My Lab ReQuest™ solution.

Based on the regulations and expected coverage for testing, for our insured patients Sonora Quest will bill the patient’s insurance directly. Uninsured patients have the option of paying a reduced cost of $75 for COVID-19 antibody testing if paid at the time of service. 

Note that there is no charge for this test as testing will be billed to insurance under a medical standing order for insured patients. Uninsured patients have the option of paying a reduced cost of $75 for COVID-19 antibody testing if paid at the time of service.

If you would like to order the COVID-19 antibody test without a doctor's order or insurance, it is available for $75 through our My Lab ReQuest™ solution.

Orders should be submitted to Sonora Quest with all patient demographics and “Uninsured” noted in the payor portion of the order. Sonora Quest will pursue payment through AHCCCS or Department of Health & Human Services and will not be charging the patient.

Note that there is no charge for this test as testing will be billed to insurance under a medical standing order for insured patients. Uninsured patients have the option of paying a reduced cost of $75 for COVID-19 antibody testing if paid at the time of service.

If you would like to order the COVID-19 antibody test without a doctor's order or insurance, it is available for $75 through our My Lab ReQuest™ solution. 

To apply for AHCCCS or to obtain additional information, patients can visit https://azahcccs.gov/Members/GetCovered/apply.html or call the Applicant & Member Services 1(855)HEA-PLUS (1-855-432-7587). Calls are answered Monday through Friday 8 a.m. – 5 p.m.

The antibody testing does not need to be on its own requisition. However, if you’re submitting both a molecular test and an antibody test, the molecular test must be submitted on its own requisition in its own specimen bag.

In medical diagnosis, test sensitivity is the ability of a test to correctly identify those with the disease (true positive rate), whereas test specificity is the ability of the test to correctly identify those without the disease (true negative rate).

In the context of the SARS-CoV-2 IgG test, sensitivity measures how often this test will accurately detect someone who has IgG antibodies to the spike protein of SARS-CoV-2, whereas, specificity measures how often this test accurately detects a negative result.

Due to cross-reactivity concerns with other human coronaviruses (HCoV-229E, HCoV-NL63, HCoV-HKU1 and HCoV-OC43) the specificity of the assay was extensively validated by the manufacturer to be highly specific. Sonora Quest has also performed our own validation using stringent acceptability criteria which consists of precision, reproducibility, accuracy, method comparison, cross reactivity and clinical performance before starting patient testing.

As stated in literature provided by Siemens Healthcare Diagnostics, analytical specificity of the ADVIA Centaur SARS-CoV-2 IgG antibody test is 99.9% (95% CI, 99.6%, 99.9%). Due to the low homology of the SARS-CoV-2 S1 protein to the human coronavirus family (HCoV-229E, HCoV-NL63, HCoV-HKU1 or HCoV-OC43), cross-reactions to most of the human pathogenic representatives of this virus family are virtually excluded.