- Serology: A blood-based serology test evaluates whether the patient carries antibodies that are triggered by the presence of the SARS-CoV-2 virus. Limitations include a substantial rate of false negative findings. Use is conditioned on the underlying rate of infection in the area where such a test is deployed as an instrument of epidemiological surveillance. Serology tests can be run as both point-of-care and lab tests, in which case an immunoassay analyzer may be used.
- PCR: Polymerase chain reaction tests (PCR) are designed to evaluate the presence of a nucleic acid in a patient sample. PCR testing evaluates viral RNA, and as is the case with serology tests, is available as both a lab and a point-of-care test. POC tests can be turned around in less than an hour, although the results of tests sent to a lab might not be available for up to a week.
- Antigen: Often used as a point-of-care test, antigen testing can detect the presence of a pathogen more quickly than antibody tests, which rely on the immune system to produce a reaction to the invader. Rapid antigen tests are commonly used for influenza and streptococcus. Lab versions are often run on immunoassay analyzers.
The equipment needed
- Immunoassay analyzer: Typically used to detect antibodies and antigens, sometimes uses antigens to detect antibodies. Examples of immunoassay analyzer test types: Enzyme-linked immunosorbent assay (ELISA), although more recently, immunoassays can be combined with real-time quantitative polymerase chain reaction (RT-qPCR) techniques, which can serve as a nucleic acid probe. Other examples include lateral flow tests and agglutination PCR.
- Chemistry analyzer: Often automated, and commonly used to detect antibodies and other naturally occurring molecules in serum, plasma and urine. Use examples include tests for cancer biomarkers and ion-selective potentiometry, as well as cell counting.
- Thermocyclers: Also known as thermal cyclers, these are used to amplify nucleic acids for PCR testing, although the cycling process may have to be repeated dozens of times to produce enough DNA or RNA. This method typically relies on a swab from mucous tissue, such as the nasal passages.
Reagents, other supplies and accessory equipment
- Types of reagents: Broadly speaking, a reagent is a chemical compound added to a process to induce a chemical reaction designed to detect a target chemical or substance. In PCR testing, a reagent is used at multiple steps, including at the stage at which viral RNA is extracted prior to amplification. Reagents are also used in antigen and serological tests. Reagents are among the supplies that have been the subject of reports of shortages during the COVID-19 pandemic.
- Centrifuges: Used in a wide variety of chemical and manufacturing processes as well as PCR tests for the SARS-CoV-2 virus to separate the viral RNA from other chemicals and molecules at several steps in the RNA isolation and amplification process. Centrifuges may be used in several types of serology testing as well.
- Pipettes: Used to contain a mix of the patient sample and reagents while the desired reaction takes place. Depending on the type of pipette, these containers can be used to provide precise volume measurement or to simply transfer a liquid. They’re also used during centrifuging.
Editor's note: This article is part of a series of stories assessing the state of the rapidly evolving COVID-19 diagnostics.