Coronavirus laboratory findings

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Syed Hassan A. Kazmi BSc, MD [2]

Overview

Laboratory tests can be done to confirm whether illness may be caused by human coronaviruses. However, these tests are not used very often because people usually have mild illness. Also, testing may be limited to a few specialized laboratories. Laboratory tests include serology for viral antigen, molecular testing and viral culture. All these tests can be used to confirm infection with coronavirus.

Laboratory Findings

COVID-19

Molecular tests

Molecular tests are used to diagnose active infection (presence of COVID-19) in people who are thought to be infected with COVID-19 based on their clinical symptoms and having links to places where COVID-19 has been reported.

• Real-time reverse-transcription polymerase chain reaction (rRT-PCR) assays are molecular tests that can be used to detect viral RNA in clinical samples.

Nucleic acid amplification test

• The importance of the need for confirmation of results of testing with pan-coronavirus primers is underscored by the fact that four human coronaviruses (HcoVs) are endemic globally: HCoV-229E, HCoV-NL63, HCoV-HKU1 as well as HCoV-OC43. The latter two are betacoronaviruses. Two other betacoronaviruses that cause zoonotic infection in humans are MERS-CoV, acquired by contact with dromedary camels and SARS arising from civets and cave-dwelling horseshoe bats.

Serological testing

• Serological testing may be useful to confirm immunologic response to a pathogen from a specific viral group, e.g. coronavirus.
• Best results from serologic testing requires the collection of paired serum samples (in the acute and convalescent phase) from cases under investigation.

Tests to be performed for patients meeting case definition
Laboratory Test	Source of Specimen	Additional Comments
In laboratories that have validated broad coronavirus RT-PCR assays it is advised to check the primers against the published 2019-nCoV sequence and check if primers are overlapping and have the capacity to detect the 2019-nCoV. On a positive results sequencing should be performed to determine the precise virus detected (e.g. on an amplicon of a non-conserved region).	Respiratory secretions	Collect on presentation. Done by an expert laboratory.
NAAT for 2019n-CoV when it becomes available (assays currently under validation)	Respiratory secretions	Collect on presentation. Done by an expert laboratory until validation has been finalized.
Serology, broad corona virus serology on paired samples if available.	Respiratory secretions	Paired samples necessary for confirmation, the first sample collected in week 1 of illness and the second collected 3-4 weeks later. If a single serum sample can be collected, collect at least 3 weeks after onset of symptoms. Done by expert laboratory until more information on performance of available assays.

MERS-CoV

Molecular tests

Molecular tests are used to diagnose active infection (presence of MERS-CoV) in people who are thought to be infected with MERS-CoV based on their clinical symptoms and having links to places where MERS has been reported.

• Real-time reverse-transcription polymerase chain reaction (rRT-PCR) assays are molecular tests that can be used to detect viral RNA in clinical samples. CDC’s current case definition for laboratory confirmation of MERS-CoV infection requires either a positive rRT-PCR result for at least two specific genomic targets, or a single positive target with sequencing of a second target.
• CDC considers a known MERS patient to be negative for active MERS-CoV infection following two consecutive negative rRT-PCR tests on all specimens.

Serology Tests

Serology testing is used to detect previous infection (antibodies to MERS-CoV) in people who may have been exposed to the virus. Antibodies are proteins produced by the body’s immune system to attack and kill viruses, bacteria, and other microbes during infection. The presence of antibodies to MERS-CoV indicates that a person had been previously infected with the virus and developed an immune response.

• CDC has a two-phase approach for serology testing, using two screening tests and one confirmatory test to detect antibodies to MERS-CoV.
• ELISA, or enzyme-linked immunosorbent assay, is a screening test used to detect the presence and concentration of specific antibodies that bind to a viral protein. CDC tests by ELISAS for antibodies against two different MERS-CoV proteins, the nucleocapsid (N) and spike (S).
• If a clinical sample is determined to be antibody-positive by either ELISA, CDC then uses the microneutralization test to confirm the positive result.
• The microneutralization assay is a highly specific confirmatory test used to measure neutralizing antibodies, or antibodies that can neutralize virus. This method is considered a gold standard for detection of specific antibodies in serum samples. However, compared with the ELISA, the microneutralization assay is labor-intensive and time-consuming, requiring at least 5 days before results are available.
• If a clinical sample is positive by either ELISA, and positive by microneutralization, the specimen is determined to be confirmed positive.
• If a clinical sample is positive by both ELISAs, and negative by microneutralization, the sample is determined to be indeterminate.
• If a clinical sample is positive by only one ELISA, and negative by microneutralization, the sample is determined to be negative.
• If a clinical sample is negative by both ELISAS, the sample is determined negative.
• In the end, a final determination of a confirmed positive serology result requires a positive ELISA test and confirmation by microneutralization assay.
• MERS-CoV serology tests are for surveillance or investigational purposes and not for diagnostic purposes—they are tools developed in response to the MERS-CoV outbreak.

SARS-CoV

• A reverse transcription polymerase chain reaction (RT-PCR) test can detect SARS-CoV in clinical specimens such as blood, stool, and nasal secretions.
• Serologic testing also can be performed to detect SARS-CoV antibodies produced after infection.
• Finally, viral culture has been used to detect SARS-CoV.