Coronavirus Disease 2019 (COVID-19)

Frequently Asked Questions


Page updated May 9, 2023Linkedin     Email
 

COVID-19 FAQs

As a trusted healthcare partner, ARUP is committed to providing timely, accurate test results that inform optimal patient care.

 
Why is testing for COVID-19 infections still important?

Testing for SARS-CoV-2 using a molecular method such as NAA (nucleic acid amplification) is recommended for symptomatic patients. Since symptoms are similar to other respiratory infections, a clinical diagnosis alone is not sufficient to make a COVID-19 diagnosis.

Are antigen “self-tests” as accurate as molecular testing?

Both antigen and molecular tests perform best when patients are symptomatic. Generally, COVID-19 antigen tests are less sensitive than molecular methods. NAA (nucleic acid amplification) testing is the recommended diagnostic test for the diagnosis of a COVID-19 infection.1

Does molecular viral detection testing detect the novel Alpha, Beta, Delta, Gamma, and Omicron variants, or other variants of SARS-CoV-2 with mutations in the spike protein (S gene)?

ARUP currently offers a COVID-19 nucleic acid amplification (NAA) assay that can be performed using either of two methodologies, reverse transcription polymerase chain reaction (RT-PCR) or transcription-mediated amplification (TMA). The RT-PCR tests are manufactured by Hologic and Roche, and the TMA test is manufactured by Hologic. The Hologic tests are performed on the Panther system, and the Roche test is run on the Cobas 6800 system. The Hologic and Roche assays do not use the S gene as an amplification target, and thus their performance is unaffected by S gene mutations.

Genetic sequencing is required to fully characterize and identify a particular SARS-CoV-2 strain. ARUP’s Hologic and Roche SARS-CoV-2 assays use several gene targets. These multiple targets allow the assays to detect genetic variants by adding redundancy.

ARUP SARS-CoV-2 Assay Gene Targets

 

AssayGene Targets
Roche RT-PCROrf1ab/O-methyltransferase (2 different sites) Env E-gene/pan-sarbecovirus
Hologic RT-PCROrf1ab/O-methyltransferase (2 different sites)
Hologic TMAOrf1ab/O-methyltransferase (2 different sites)

The assays can detect the Alpha, Beta, Delta, Gamma, and Omicron variants of SARS-CoV-2. Currently, there have been no detected mutations or viral variants that will not be detected by the assay offered by ARUP Laboratories. There is no difference in treatment based on the specific SARS-CoV-2 variant.

More information about COVID-19 variants can be found on the CDC’s website.2 Additionally, you can refer to this U.S. Food and Drug Administration (FDA)3 resource for more information about SARS-CoV-2 variants and their possible impact on laboratory testing.

Does ARUP have a SARS-CoV-2 sequencing test available to order? What steps is ARUP taking to identify major variants and to determine how they impact laboratory testing?

ARUP does not currently offer a SARS-CoV-2 sequencing test to clients. ARUP is required to send a percentage of positive specimens to the state health department for sequencing and variant identification for public health management.

Hologic and Roche, the manufacturers of the platforms used by ARUP to perform NAA testing, are continuously monitoring available sequences of SARS-CoV-2 strains to ensure that their assays are detecting emerging variants and to understand any implications of these mutations. Currently, there have been no detected mutations or viral variants that will not be detected by the assay offered by ARUP Laboratories.

What is the difference between IgM, IgG, and IgA antibodies? Is it necessary to be tested for all of them?

Generally, immunoglobulin M (IgM) antibodies are the first antibodies the body produces in response to an infection, usually appear within a week of infection, and disappear within a month or two. IgG antibodies typically develop after IgM and may remain detectable for months or years, although the time period that IgG antibodies persist in those who have had COVID-19 is still being determined. However, in COVID-19, IgM and IgG develop almost simultaneously, generally 7–14 days after symptom onset, in response to SARS-CoV-2 infection. IgM antibodies persist for only a few weeks, whereas IgG levels are more durable and can sometimes be detected for months after natural infection. IgA and standalone IgM tests are not recommended for SARS-CoV-2 serology testing.4 Total antibody and IgG assays should be used instead. Several studies have reported detectable IgG response several months after infection or vaccination using IgG assays.

Can serology be used to determine vaccine response?

COVID-19 vaccination produces antibodies against the SARS-CoV-2 spike protein. These antibodies can be detected by several serology tests, including ARUP’s COVID-19 IgG (Spike), Semi-Quantitative by CIA (3003648) assay. However, it has not yet been established that the presence of SARS-CoV-2 IgG antibodies implies protective immunity. Data are insufficient to define a threshold for protective immunity, so we cannot properly interpret whether or not a patient is protected from symptomatic disease or reinfection. The American Association for Clinical Chemistry (AACC) does not currently recommend the use of serology to assess vaccination response.4

What do the results of my molecular diagnostic and/or serology test mean?

The table below details the potential results of molecular diagnostic or serology assays and their interpretations.

TestResultaInterpretation
COVID-19 molecular diagnostic assaysPositiveA positive result indicates the detection of nucleic acid from COVID-19 and an active COVID-19 infection. Positive results do not rule out bacterial infection or coinfection with other viruses.
NegativeThe person tested most likely did not have an active COVID-19 infection at the time the specimen was collected. Infection may still occur at a later time.
False-negative results are possible; a negative result must be combined with other clinical observations, patient history, and epidemiologic information to rule out infection. Retesting might be recommended if a clinician still suspects COVID-19.
IndeterminateThe test was neither clearly positive nor clearly negative. Retesting after a period of time may be appropriate.
InvalidTest results could not be determined. This result could be due to the presence of interfering or inhibiting substances in the specimen. Retesting after a period of time may be appropriate.
COVID-19 serology assaysPositiveAntibodies to SARS-CoV-2 were detected. It is likely that the patient has been exposed to SARS-CoV-2. Serology assays that detect antibodies to the spike protein may also detect antibodies generated in response to COVID-19 vaccination.
A positive result does NOT guarantee either current or future immunity to the virus. Researchers do not know how long COVID-19 IgG antibodies persist, or the level and duration of protection that they may provide.
NegativeAntibodies to SARS-CoV-2 were not detected. This could suggest that an exposure did not occur, that an exposure occurred too recently for an antibody response to develop, or that an exposure did not result in the production of enough antibodies to be detected by the test. Negative antibody test results do not rule out SARS-CoV-2 infection.
IndeterminateThe test was neither clearly positive nor clearly negative. Retesting after a period of time may be appropriate.

Source: CDC, 20215,6

aReliable results are dependent on adequate specimen collection, transport, storage, and processing.

Is there a chance that molecular test results could be inaccurate?

No test is perfect. Occasionally, tests can yield a false-positive or false-negative result. Molecular diagnostic testing is highly specific, meaning that the test is designed to detect the unique genetic sequence of SARS-CoV-2. If a test result is positive, you can be confident that the virus was detected.

False-negative results may occur depending on the specimen tested and the timing of the sample collection. If testing is performed early in the infectious process, before symptoms occur, test results may be falsely negative. A false-negative result is also possible if a person is tested late in the course of the infection, when symptoms have waned.

Is there a chance that antibody test results could be inaccurate?

No test is perfect. Occasionally, antibody tests can return false-positive or false-negative results. If a specimen is collected too early, antibody tests can yield false-negative results. False-positive results are possible in a small percentage of individuals. These may be due to past or present infection with non-SARS-CoV-2 coronavirus strains, such as coronavirus HKU1, NL63, OC43, or 229E.

These and other serology tests for COVID-19 offered by ARUP have been evaluated by both the manufacturer and the U.S. Food and Drug Administration (FDA) in partnership with the National Institutes of Health (NIH), the CDC, and the Biomedical Advanced Research and Development Authority (BARDA). Please visit the FDA web page, EUA Authorized Serology Test Performance, for more information.

Performance of COVID-19 IgG (Spike), Qualitative by CIA
AntibodyPerformance MeasureEstimate of Performance95% CI
IgGSensitivity100% (88/88)95.8% to 100%
IgGSpecificity99.6% (1,066/1,070)99.0% to 99.9%
IgGPPV at prevalence = 5%93.4%84.0% to 97.3%
IgGNPV at prevalence = 5%100%99.8% to 100%

CI, confidence interval; NPV, negative predictive value; PPV, positive predictive value

Source: FDA, 20227

Performance of COVID-19 IgG (Spike), Semi-Quantitative by CIA
Performance MeasureEstimate of Performance
Sensitivity (PPA)100% (42/42)
Specificity (NPA)99.9% (1,829/1,831)
PPV at prevalence = 5%98.0%
NPV at prevalence = 5%100%
Source: FDA, 20227

References

  1. U.S. Department of Health and Human Services, Centers for Disease Control and Prevention. Guidance for antigen testing for SARS-CoV-2 for healthcare providers testing individuals in the community. [Updated: Apr 2022; Accessed: Apr 2023]
  2. U.S. Department of Health and Human Services, Centers for Disease Control and Prevention. SARS-CoV-2 variant proportions. [Accessed: Apr 2023]
  3. U.S. Department of Health and Human Services, Food and Drug Administration. SARS-CoV-2 viral mutations: impact on COVID-19 tests. [Last reviewed: Mar 2023; Accessed: Apr 2023]
  4. Zhang YV, Wiencek J, Meng QH, et al. AACC practical recommendations for implementing and interpreting SARS-CoV-2 emergency use authorization and laboratory-developed test serologic testing in clinical laboratories. Clin Chem. 2021;67(9):1188-1200.
  5. U.S. Department of Health and Human Services, Centers for Disease Control and Prevention. Overview of testing for SARS-CoV-2, the virus that causes COVID-19. [Updated: Sep 2022; Accessed: Apr 2023]
  6. U.S. Department of Health and Human Services, Centers for Disease Control and Prevention. Interim guidelines for COVID-19 antibody testing. [Accessed: Apr 2023]
  7. U.S. Department of Health and Human Services, Food and Drug Administration. EUA authorized serology test performance. [Last reviewed: Aug 2022; Accessed: Apr 2023]