Novel Coronavirus Disease 2019 (COVID-19) Testing

  • Use to detect COVID-19 in specimens obtained during the acute phase of infection from individuals who meet COVID-19 clinical and/or epidemiologic criteria; nasopharyngeal specimens are preferred 
  • This test is specific to SARS-CoV-2 and does not detect additional coronaviruses
  • This test is available under the FDA’s Emergency Use Authorization (EUA)
  • Use for the qualitative detection of IgG antibodies against the nucleocapsid protein of SARS-CoV-2 in serum and plasma to evaluate exposure
  • Not recommended for COVID-19 diagnosis
  • The use of two different antibody assays in an orthogonal testing algorithm may reduce the likelihood of a false-positive result
  • The presence of IgG antibodies does not indicate protective immunity
  • Test is available under the FDA’s Emergency Use Authorization (EUA)
  • Use for the detection of IgG antibodies against the spike protein (S1) of SARS-CoV-2 in serum and plasma to evaluate exposure
  • Not recommended for COVID-19 diagnosis
  • The use of two different antibody assays in an orthogonal testing algorithm may reduce the likelihood of a false-positive result
  • The presence of IgG antibodies may not indicate protective immunity
  • Test is available under the FDA’s Emergency Use Authorization (EUA)

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) causes the novel coronavirus disease 2019 (COVID-19) and has led to a pandemic and a national public health emergency in the United States. The environment surrounding COVID-19 testing is continually evolving, and clinicians are encouraged to consult the CDC for the most current testing priorities and recommendations. 

Identification of patients infected with SARS-CoV-2 can help to isolate cases and prevent further person-to-person transmission, thus slowing the spread of infection, limiting the number of cases, and mitigating the impact on healthcare resources.  

Molecular diagnostic testing by nucleic acid amplification (NAA) or PCR is recommended for SARS-CoV-2 diagnosis.  Testing decisions should be based on local epidemiology, clinical signs and symptoms, and the course of illness.

Serology testing is used to detect antibodies to SARS-CoV-2. This testing can be used to evaluate patients for exposure, but is not recommended for COVID-19 diagnosis. Early studies suggest that most patients seroconvert approximately 2 weeks after symptom onset.

False-positive results are possible in low-prevalence settings, even when an antibody test has >98.0% specificity. To reduce the likelihood of a false-positive result, the CDC Interim Guidelines for COVID-19 Antibody Testing   suggest testing individuals with a high pretest probability, choosing a test with a high specificity, or using an orthogonal testing algorithm so that individuals who are positive by one antibody test are retested with a second antibody test. The two antibody tests offered by ARUP are complementary, as they target different proteins of SARS-CoV-2. As such, they can be used together in an orthogonal algorithm to maximize the positive predictive value of testing and minimize false-positive results.

Disease Overview

Incidence

In early 2020, COVID-19 spread rapidly across the globe. Updated case counts can be found in the World Health Organization’s Coronavirus disease (COVID-2019) situation reports  and on the CDC’s Cases in the U.S. web page. 

Symptoms

Clinical presentation ranges from asymptomatic infection to mild, acute upper respiratory symptoms to more severe flulike illness and pneumonia. Symptoms may appear 2-14 days after exposure.   Symptoms of possible COVID-19 include fever, cough, shortness of breath or difficulty breathing, chills, myalgia, headache, new loss of taste or smell, nausea or vomiting, diarrhea, and sore throat. 

Emergency warning signs of COVID-19 include the following :  

  • Difficulty breathing
  • Persistent pain or pressure in the chest
  • New confusion
  • Inability to wake or remain awake
  • Bluish lips or face

Transmission

  • The virus spreads through respiratory droplets produced when an infected person coughs, sneezes, or talks. 
  • These respiratory droplets can pass into the mouths or noses of people nearby or may be inhaled. 

Test Interpretation

Molecular Diagnostic Test (NAA)

Results

Results are reported as SARS-CoV-2 detected, not detected, or invalid.

Specificity

This test detects the 2019 novel coronavirus strain (SARS-CoV-2). It was shown by the manufacturer by direct testing or in silico analysis to not cross-react with a large number of other bacteria and viruses.

Limitations

  • Negative results do not preclude SARS-CoV-2 infection and should not be used as the sole basis for patient management decisions. 
  • Negative results must be combined with other clinical observations, patient history, and epidemiologic information. 
  • A positive result indicates the detection of nucleic acid from the relevant virus. 
    • Nucleic acid may persist even after the virus is no longer viable.
  • Positive results do not rule out bacterial infection or coinfection with other viruses. 
  • Reliable results are dependent on adequate specimen collection, transport, storage, and processing. 

COVID-19 IgG (Serology)

COVID-19 IgG, Qualitative by CIA

This CIA assay, developed by Abbott and performed on the Architect platform, detects IgG antibodies specific to the nucleocapsid protein of SARS-CoV-2. This test is reported as negative or positive.

This and other serology tests for COVID-19 have been evaluated by both the manufacturer and the 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, Qualitative by CIA
Antibody Performance Measure Estimate of Performance 95% CI

IgG

Sensitivity

100% (88/88)

95.8% to 100%

IgG

Specificity

99.6% (1,066/1,070)

99% to 99.9%

IgG

PPV at prevalence = 5%

92.9%

83.4% to 98.1%

IgG

NPV at prevalence = 5%

100%

99.8% to 100%

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

Data source:  https://www.fda.gov/medical-devices/emergency-situations-medical-devices/eua-authorized-serology-test-performance 

COVID-19 IgG by ELISA

This ELISA assay, developed by EUROIMMUN, detects IgG antibodies specific to the S1 domain of the spike protein of SARS-CoV-2. This test is reported as negative, indeterminate, or positive, and will include an index value.

This and other serology tests for COVID-19 have been evaluated by both the manufacturer and the FDA in partnership with the NIH, the CDC, and BARDA. Please visit the FDA web page, EUA Authorized Serology Test Performance for more information. 

Performance of COVID-19 IgG by ELISA
Antibody Performance Measure Estimate of Performance 95% CI

IgG

Sensitivity

90% (27/30)

74.4% to 96.5%

IgG

Specificity

100% (80/80)

95.4% to 100%

IgG

PPV at prevalence = 5%

100%

46% to 100%

IgG

NPV at prevalence = 5%

99.5%

98.6% to 99.8%

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

Data source: https://www.fda.gov/medical-devices/emergency-situations-medical-devices/eua-authorized-serology-test-performance 

Serology Limitations

  • Antibody test results should not be used as the sole criterion to confirm or rule out SARS-CoV-2 infection or to assess infection status.
  • Negative results do not exclude infection with SARS-CoV-2, especially in individuals with known exposure to the virus.
    • Follow-up molecular diagnostic testing should be considered in those with recent exposure to COVID-19.
    • Immunocompromised patients infected with COVID-19 may have a delayed antibody response or antibody levels too low to result in a positive test.
  • Positive results suggest exposure to SARS-CoV-2, but may not indicate immunity.
  • False-positive results may be due to past or present infection with non-SARS-CoV-2 coronavirus strains, such as coronavirus HKU1, NL63, OC43, or 229E.
  • False-positive results are possible in low-prevalence settings, even when an antibody test has >98.0% specificity; the use of two different antibody assays is recommended to reduce the likelihood of a false-positive result (refer to the CDC Interim Guidelines for COVID-19 Antibody Testing  ).
  • Serology tests are not for use in screening donated blood.

References