Types of COVID-19 Diagnostic Tests.
- Antigen tests
- Molecular Tests
Antigen tests. Antigen tests are immunoassays that detect the presence of specific viral antigens that indicate an existing viral infection. Currently, antigen testing is permitted by placing nasopharyngeal, nasal swabs, or saliva samples directly into assay buffers or extraction reagents. A positive test result using a virus test (NAAT or antigen) with signs or symptoms consistent with COVID-19 indicates that the person has COVID-19, which is the person's vaccination status.
- The most common types are rapid or point-of-care tests that give fast results and can be taken anywhere.
- Mostly very fast
- Often cheaper than PCR (lab) tests.
- Try to be less precise when the result is negative.
- This means you may get a "false negative" result. For example, your rapid test may show that you are negative for active COVID-19 infection. But a PCR test can show that you are indeed positive. Sometimes testing more frequently can overcome some of these problems.
Molecular Test: PCR (Polymerase Chain Reaction). PCR is fundamental to many procedures used in genetic testing and research, including the analysis of ancient DNA samples and the identification of infectious agents. Using PCR, copies of very small amounts of DNA sequences are rapidly amplified in a series of cycles of temperature changes. PCR is now a common and often indispensable technique used in medical laboratory research for a wide variety of applications, including biomedical research and criminal forensics.
- Done in the laboratory.
- Considered the most accurate testing option.
- Usually takes longer. This is because the tests must be sent to a laboratory, which often takes at least a few hours.
A basic PCR setup requires several components and reagents, including:
- A DNA template amplifies the DNA target region.
- DNA polymerase; An enzyme that polymerizes new DNA strands. Heat-stable Taq polymerase is particularly common, as it is more likely to persist during high-temperature DNA degradation processes.
- Two DNA primers complementary to the 3' (three prime) ends of each of the sense and antisense strands of the DNA target (DNA polymerase can only bind to and elongate from the double-stranded region of DNA; without primers, there is no double-stranded primer site to which the polymerase can bind; specific primers that are complementary to the target region of DNA are preselected and are often custom-made in the laboratory or commercially available. Biochemicals are purchased from suppliers.
- Deoxy nucleoside triphosphates, or dNTPs (sometimes called "deoxynucleotide triphosphates"; nucleotides containing triphosphate groups), are the building blocks from which DNA polymerase synthesizes a new DNA strand.
- A buffer solution provides a suitable chemical environment for optimal activity and stability of DNA polymerase
- Bivalent cations, usually magnesium (Mg) or manganese (Mn) ions; Mg2+ is the most common, but Mg2+ can be used for PCR-mediated DNA mutagenesis, as high concentrations of Mg2+ increase the error rate during DNA synthesis. and monovalent cations, usually potassium (K) ions.
Antibody Test. Antibody tests (also called serological tests) can detect antibodies to SARS-CoV-2 in the blood. Antibodies are proteins your immune system makes to fight infection and protect against future disease. Antibody tests should not be used to diagnose a current infection, but they can tell if you have had an infection in the past. Antibody tests help us learn how a person's immune system protects against viruses and defenses at the population level. If you have had an antibody test after vaccination, some, but not all, of the antibody tests, may be positive. It depends on the type of antibodies detected by a particular test.
- Antibody testing is not currently recommended to determine:
- If you currently have an infection.
- If you are immune to SARS-CoV-2 after being vaccinated against COVID-19.
- Do I need revaccination after being vaccinated against COVID-19?
- If you need to isolate after known or suspected exposure to COVID-19.
When should I get tested?
If you have symptoms. Get tested as soon as you experience symptoms of COVID-19, whether or not you have been vaccinated. If the antigen test is negative, do another test within 24 to 48 hours. This is because the first cases are not always detectable.
If it is displayed. People exposed to COVID-19 should consider getting tested as soon as possible, even if they don't have symptoms. Repeat the test 5 days after exposure.
If you go to a high-risk event. Test before and 3-5 days after the event. For large events with more than 1,000 people, it is strongly recommended that attendees get tested 1 day (antigen test) or 2 days (PCR test) before the event.
If you are traveling. Test before and 3-5 days after the event. Anyone entering or re-entering California must be tested 3-5 days after their arrival, regardless of whether they have been vaccinated.
The types of PCR tests vary based on the sample involved. Common types include:
- Nasal swab: This involves swabbing the back of the nose and throat to take a sample.
- Nasal middle turbinate swab: Often referred to as an "NMT" swab, this involves taking a sample deep inside the nostril.
- Sputum: Giving this sample involves putting saliva into a tube.
- Blood: Some types of PCR tests require a blood sample, which is collected from a vein.
