Laboratory Testing for COVID-19

Worldwide, millions have been infected in the COVID-19 pandemic, and hundreds of thousands have died.1 Laboratory testing for COVID-19 plays a crucial role in addressing the pandemic. Identifying active COVID-19 infections assists in limiting the spread of the disease and directing the allocation of medical resources,2,3 and helps guide planning to ease social isolation restrictions.4 Importantly for healthcare providers, testing can help guide when to return to work after an infection (see Sidebar).5 

This article discusses current laboratory testing for the diagnosis of COVID-19 and assessment of past infection. 

The information in this article was current at the time of writing. However, the pandemic is evolving rapidly and new data are accumulating daily. Readers are encouraged to review the latest information on COVID-19 available at
COVID-19 Transmission and Clinical Course
COVID-19 is a clinical disease caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and is thought to be primarily spread via respiratory droplets.2 People can shed viral particles and transmit infection before exhibiting symptoms.2,6 People who never develop symptoms can still shed virus and transmit the virus to others.2,6 As such, asymptomatic transmission has proven a challenge in managing the pandemic.

The median time from exposure to symptom onset is reported to be 4 to 5 days, and approximately 98% of persons who develop symptoms will do so within 11 days after infection.6 Signs and symptoms at disease onset are typically consistent with an upper respiratory tract infection; fever and cough are most commonly observed.2,6 However, symptoms can be highly variable, and studies are ongoing to identify symptom trends associated with COVID-19 infection. For more information consult

Around 80% of people with COVID-19 have a mild and self-limiting infection requiring only supportive therapy.2,6 Approximately 15% will develop a serious illness associated with hypoxia, while 5% to 7% will develop a critical illness with multi organ-failure that requires intensive care, which may include mechanical ventilation, transfusions of blood products, and other supportive care.2,6
Laboratory Diagnosis of Current, Recent, or Past Infection

Current Infection
A definitive diagnosis of a current COVID-19 infection can be made by identifying viral genetic material (RNA) in a person’s respiratory system using molecular techniques.3,7 These techniques usually involve nucleic acid amplification tests (NAAT) based on real-time reverse transcription-polymerase chain reaction (real-time RT-PCR).3 Rapid testing for viral antigens has been recently developed; however, these tests are not as sensitive as molecular techniques for detecting active infections.8 Regardless of the method employed for COVID-19, testing should have received emergency use authorization (EUA) from the FDA.

The CDC recommends using a viral (nucleic acid or antigen) test to diagnose acute infection.7 Antibody testing (see Recent or Past Infection) is not recommended by the CDC for acute infections.7

For initial diagnostic testing for SARS-CoV-2, the CDC recommends collecting and testing an upper respiratory tract specimen. Nasal, nasopharyngeal, or oropharyngeal specimens are acceptable when collected according to CDC guidelines. Suboptimal collection techniques increase the chance of obtaining false-negative test results.9 Accordingly, the CDC provides guidance on the use of washes/aspirates and swabs, which specimens should be collected by a healthcare professional, and when supervised on-site or home self-collection is appropriate.9 Less invasive sampling methods include mid-turbinate or anterior nares specimens as the source for viral nucleic acid testing.9

Testing lower respiratory tract specimens is also an option, either from sputum from a noninduced productive cough, or from a lower respiratory tract aspirate or bronchoalveolar lavage.9

A positive test result for SARS-CoV-2 (COVID-19) in a symptomatic patient indicates that viral RNA was detected; the patient is infected with the virus and is presumed to be contagious. For asymptomatic individuals, detection of viral RNA does not necessarily mean that viable infectious virus is present. Prolonged detection of RNA without direct correlation to viral culture has been reported.5 However, because there are no symptoms, it is not possible to gauge where these patients are in the course of the infection. Thus, asymptomatic patients who test positive for SARS-CoV-2 RNA should also be considered contagious (see Sidebar).7

A “not detected” (negative) test result means that SARS- CoV-2 RNA was not present in the specimen above the limit of detection. A negative result does not rule out the possibility of COVID-19, however, and should not be used as the sole basis for treatment or patient management decisions.

An “inconclusive” result means not all of the viral RNA targets were detected. The sample may have viral concentrations near the limit of detection of the test, or other factors may have influenced the result, and an additional sample collection may be requested. 
Recent or Past Infection
Recent or past infection is assessed using serum specimens through detection of antibodies produced in the adaptive immune response to SARS-CoV-2. Data suggest that IgG antibodies can be detected beginning approximately 10 days after SARS-CoV-2 exposure or post symptom onset.10 However, it is not known how long they persist or whether they confer protective immunity. The production of IgG antibodies can also be affected by the viral burden upon exposure to SARS- CoV-2, an individual’s unique immune response, or underlying medical condition (eg, immunosuppression).10 As such, results of IgG testing should be interpreted with caution.
  • Some IgG-positive individuals may still have detectable viral RNA several weeks following seroconversion. Research efforts are ongoing to understand whether seropositive individuals who continue to shed SARS-CoV-2 RNA are infectious to others.
  • False-positive IgG antibody results, though rare, may occur due to cross-reactivity from prior non-COVID-19 coronavirus infections.
  • IgG-negative individuals may have an acute infection, which should be diagnosed by direct testing via molecular methods for SARS-CoV-2 viral RNA.
  • False-negative results may occur early in the disease course, especially when symptoms are mild.10
Who Should be Tested for Current, Recent, or Past COVID-19 Infection?

Current Infection
The CDC provides guidance with respect to testing priorities for a current, active COVID-19 infection.7 Individuals considered “high priority” for testing include
  • Hospitalized patients with symptoms
  • Healthcare facility workers, workers in congregate living settings, and first responders with symptoms
  • Residents in long-term care facilities or other congregate living settings, including prisons and shelters, with symptoms
Individuals considered a “priority” for testing include
  • Persons with symptoms of potential COVID-19 infection, including fever, cough, shortness of breath, chills, muscle pain, new loss of taste or smell, vomiting or diarrhea, and/or sore throat
  • Persons without symptoms who are prioritized by health departments or clinicians, for any reason including, but not limited to, public health monitoring, sentinel surveillance, or screening of other asymptomatic individuals according to state and local plans
Recent or Past Infection
The CDC advises patients to consult their healthcare providers about antibody testing for past infection.11 Thus, who is tested is at the discretion of the healthcare provider. 
Test-based Criteria for Return to Work for Healthcare Personnel with Suspected or Confirmed COVID-19

Healthcare providers are at the forefront of managing the pandemic. Despite precautions, healthcare providers occasionally do contract COVID-19 infections. The CDC has established symptom- and test-based strategies for establishing when healthcare providers with a suspected or confirmed COVID-19 infection can return to work.5

For the test-based strategy, healthcare workers with a suspected COVID-19 infection or a confirmed asymptomatic COVID-19 infection should not return to work until negative results are obtained for detection of SARS-CoV-2 RNA using an FDA EUA COVID-19 molecular assay from at least 2 consecutive respiratory specimens collected ≥24 hours apart. In addition
  • For suspected infections, fever must have resolved without the use of fever-reducing medications and respiratory symptoms must have improved.
  • For confirmed asymptomatic infections,10 days should have passed since the date of their first positive COVID-19 diagnostic test, assuming they have not subsequently developed symptoms since their positive test result.
The CDC indicates that infectious disease experts should be consulted when making return-to-work decisions for the immunocompromised and those who may be infectious >10 days.5,6

For full details, including the symptom-based strategy, see the interim guidance at
How the Laboratory Can Help

Quest Diagnostics is committed to assisting healthcare providers during the current COVID-19 global pandemic, and is a leader in the development of COVID-19 diagnostic testing.

Testing for Current Infection
The Quest SARS-CoV-2 RNA (COVID-19), Qualitative NAAT (test code 39448) identifies the presence of viral genetic material in respiratory specimens and can be used to aid in the diagnosis of COVID-19. The test has been authorized by the FDA under an EUA.

Information about the test is available at

Testing for Recent or Past Infection
The SARS-CoV-2 Serology (COVID-19) Antibody (IgG), Immunoassay (test code 39504) determines the presence of antibodies (IgG) to SARS-CoV-2. This test can be used for
  1. Detection of SARS-CoV-2 antibodies in asymptomatic individuals who have been exposed and have mounted an immune response
  2. Evaluation of recovered individuals for convalescent plasma donations
  3. Population-level seroprevalence studies
This test has a sensitivity of approximately 90% to 100% for PCR-positive specimens and a specificity of 99% to 100% (<1% of pre-COVID panels of samples from 2010, 2017 and 2019 give positive results).12-14

Frequently asked questions about the test can be viewed at

Notes regarding COVID-19 testing at Quest:
  • The antibody tests and the molecular tests (together “All tests”) have not been FDA cleared or approved.
  • All tests have been authorized by FDA under EUAs 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.
  • The molecular tests have been authorized only for the detection of nucleic acid from SARS-CoV-2, not for any other viruses or pathogens.
  • All 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.

For the latest information on COVID-19 testing please visit:

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  1. WHO coronavirus disease (COVID-19) dashboard. World Health Organization. Updated May 4, 2020. Accessed May 4, 2020.
  2. Cascella M, Rajnik M, Cuomo A, et al. Features, evaluation and treatment coronavirus (COVID)-19. In: StatPearls [Internet]. StatPearls Publishing; 2020. Updated April 6, 2020. Accessed May 1, 2020.
  3. Tang YW, Schmitz JE, Persing DH, et al. The laboratory diagnosis of COVID-19 infection: current issues and challenges. J Clin Microbiol. 2020;JCM.00512-20. doi:10.1128/JCM.00512-20
  4. Guidelines: opening up America again. The White House. Accessed May 13, 2020.
  5. Criteria for return to work for healthcare personnel with suspected or confirmed COVID-19 (interim guidance). Centers for Disease Control and Prevention. Reviewed May 2, 2020. Accessed May 12, 2020.
  6. Interim clinical guidance for management of patients with confirmed coronavirus disease (COVID-19). Centers for Disease Control and Prevention. Reviewed April 6, 2020. Accessed April 15, 2020.
  7. Evaluating and testing persons for coronavirus disease 2019 (COVID-19). Centers for Disease Control and Prevention. Updated May 5, 2020. Accessed May 12, 2020.
  8. Coronavirus (COVID-19) update: FDA authorizes first antigen test to help in the rapid detection of the virus that causes COVID-19 in patients. U.S. Food & Drug Administration. May 9, 2020. Accessed May 20, 2020.
  9. Interim guidelines for collecting, handling, and testing clinical specimens from persons for coronavirus disease 2019 (COVID-19). Centers for Disease Control and Prevention. Updated May 5, 2020. Accessed May 12, 2020.
  10. IDSA COVID-19 antibody testing primer. Infectious Diseases Society of America. Updated May 4, 2020. Accessed May 13, 2020.
  11. Test for past infection. Centers for Disease Control and Prevention. Updated May 5, 2020. Accessed May 12, 2020.
  12. Anti-SARS-CoV-2 ELISA (IgG). Instructions for use. Euroimmun; March 2020.
  13. Abbott Architect SARS-CoV-2 IgG. Package insert. Abbot; April 2020.
  14. VITROS Immunodiagnostic Products Anti-SARS-CoV-2 IgG. Instructions for use. April 2020

Content reviewed 6/2020