Types Of Covid Tests

There are two broad types of COVID lab tests, distinguished by the method they use to detect infection:

1. Viral Testing – Per CDC, any authorized assay for viral testing that detect either SARS-CoV-2 nucleic acid or antigen. Recommended to diagnose acute infection of both symptomatic and asymptomatic individuals, to guide contact tracing, treatment options, and isolation requirements. There are two major subtypes:
   - a Antigen Testing - fast (<15 minutes) on-site testing that identifies COVID-specific structural components. Relatively inexpensive, but also less sensitive (higher chance of missing positive cases). Previously referred to as “Rapid Antigen Tests.” Renamed by the CDC in December 2020. May require Nucleic Acid Amplification Tests (NAAT) confirmatory testing under certain circumstances. Current FDA EUAs for antigen tests limits their use to symptomatic patients within a certain number of days of symptoms onsets. Special authorization was granted to the DoD by the FDA to use for serially screening asymptomatic individuals in certain circumstances.
   - b NAATs - slower (1 hour - 2 days) in-lab testing that initiates an exponential multiplication of COVID nucleic acid. More expensive, but higher sensitivity (lower chance of missing positive cases) and specificity (lower chance of falsely identifying a true negative as positive) compared to antigen tests. Most common subtype is reverse transcription-polymerase chain reaction (RT-PCR) testing.
2. Antibody Testing - in-lab test identifies the immune response to COVID (antibodies). The FDA has not authorized antibody tests to diagnose SARS-CoV-2. It is not approved for diagnosing current infection but may help determine whether an individual was previously infected. Issues with cross-reactivity to other similar virus antibodies. Commonly used for surveillance testing and epidemiologic studies.

RESOURCES:

Overview of Testing for SARS-CoV-2 (COVID-19)

Interim Guidance for Antigen Testing for SARS-CoV-2

Using Antibody Tests for COVID-19

Covid Testing Strategies

There are also three broad categories for COVID testing strategies by the CDC:

1. Diagnostic - used to identify current infection in symptomatic patients or asymptomatic close-contacts.
2. Screening - used to identify infected persons who are asymptomatic and without known or suspected exposure. Screening testing is performed to identify persons who may be contagious so that measures can be taken to prevent further transmission.
3. Surveillance - used to gain information at a population level with de-identified results returning in aggregate and not to the individual. It is intended to monitor community - or population-level outbreak of disease, or to characterize the incidence and prevalence of disease.
4. Surveillance testing cannot be used for individual decision-making.