COVID-19 – Tests and Testing
Questions that needs to be answered before performing or adminstering a COVID-19 test#
- Why do we want to perform a test?
- What types of tests for COVID-19 are available?
- What information will a specific test provide?
- How are test results interpreted (see Glick M. YouTube below?
- How accurate and reliable are the test results?
- What are the implications of a test result?
- What we intend do with the test result?
Tests#
Detecting the virus#
Molecular tests#
- Real-time reverse transcription polymerase chain reaction (qRT-PCR) With the aid of a special swab, samples from saliva, the naso- and oropharynx, as well as sputum are collected detect presence of viral RNA.
- Reverse transcription loop-mediated isothermal amplification (RT-LAMP) RT-LAMP also detects presence of viral RNA. This technique is more robust and quicker than rRT-PCR.
- Clustered regularly interspaced short palindromic repeats – CRISPR A qualitative test for the detection of nucleic acid from SARS-CoV-2.
Antigen test#
- Lateral flow immunofluorescent sandwich assay. For the identification of SARS-CoV-2 nucleocapsid protein antigen.
Detecting antibodies#
Antibody testing is multipurpose: it can verify that vaccines are working or be used in contact tracing weeks or longer after a suspected infection in an individual. Antibodies reveal evidence of a previous infection any time from about a week after the infection occurred
- Enzyme-linked immunosorbent assay (ELISA), Chemiluminescence enzyme immunoassays (CLIA), Fluorescence immunoassays (FIA), and Lateral flow immunoassays (LFIA) Several different antibody tests have been approved to detect total and specific antibodies against SARS-CoV-2 from serological samples.
Tests and test interpretation#
(From Coronavirus Disease 2019 Testing Basics. Food and Drug Administration (FDA)
| Molecular Test | Antigen Test | Antibody Test | |
|---|---|---|---|
| Other names used for a test | Diagnostic test, viral test, molecular test, nucleic acid amplification test (NAAT), reverse transcriptase polymerase chain reaction (RT-PCR) test, real time PCR (qPCR), real time RT-PCR (qRT-PCR), reverse transcription loop-mediated isothermal amplification (RT-LAMP) | Diagnostic test, viral test, rapid test | Serological test, serology |
| Sample collection | Nasal/nasopharyngeal swabs, saliva | Nasal/nasopharyngeal swabs | Blood from fingerstick or vein |
| Interpretation | Active COVID-19 infection | Possible active COVID-19 infection. Positive test should be confirmed with a molecular test. Higher false-negative rates compared to NAAT among asymptomatic individuals. | Indicates either acute infection, late-stage acute infection, or past infection. Can also differentiate between antibodies that developed due to an infection (presence of nucleoid capsid protein antibodies) and antibodies due to vaccination (no nucleoid capsid protein antibodies). |
| Test Result | Clinical Significance | ||
|---|---|---|---|
| PCR | IgM | IgG | |
| + | - | - | Possible window period (virus present but no signs or symptoms) |
| + | + | - | Early stage of infection |
| + | + | + | Acute stage of infection |
| + | - | + | Late or recurrent stage of infection |
| - | + | - | False-negative PCR in the early stage of infection |
| - | - | + | Past infection or in recovery |
| - | + | + | False-negative PCR but in active or recovery state of infection |
| - | - | - | False-negative PCR, false-negative antibody test, or never infected |
Related Pages#
References/Websites#
References
Websites
- CDC’s Diagnostic Test for COVID-19 Only and Supplies. Centers for Disease Control and Prevention. August 17, 2021.
- Coronavirus Disease 2019 Testing Basics. Food and Drug Administration (FDA). April 2021.
- LitCovid. U.S. National Library of Medicine.
- Glick M. If testing, what is the chance your patient is positive for COVID-19? YouTube. May 5, 2020.