According to Johns Hopkins University, there are now around 500 different tests in the world for detecting the SARS-CoV-2 coronavirus in the body. They can be roughly divided into three groups: PCR tests, antigen tests, and serological antibody tests. All of them show the virus’s presence in the body at the time of the test, and the third one determines whether a person was previously infected.
PCR tests
The classic PCR test is strictly carried out in laboratories. A long Q-tip is inserted into the cavity between the nose and mouth of the patient, then examined for RNA virus presence. Samples can be collected at home. While the smear analysis itself takes several hours, results are reported after 1–2 days.
Accuracy: 70–80 percent
The test often has false-negative results. Common causes include improper patient preparation, sampling technique, incorrect transportation or storage, and testing is too late or early.
When to get tested?
For the most reliable results, you should take the PCR test on the second or third day after symptoms first appear.
Test preparation: two hours before the test, avoid eating and drinking, brushing your teeth, chewing gum, smoking, taking medication, using antiseptics, using nasal or mouth sprays.
The first test for home use
The United States FDA has approved an at-home test developed by Lucira. It will be available in the United States by prescription. The kit contains sterile sticks for a self-swab from the nose, a test tube, and the device itself for determining the virus.
The result appears after 30 minutes—the color of the indicator will change on the display. The test is based on the LAMP method, which, like the PCR test, copies the genetic material of the virus multiple times until it reaches a detectable level. Currently, this test is considered to be less accurate than the PCR.
AG tests—antigen tests
Speed is the main advantage of express antigen tests over PCR tests. With a cotton swab, a saliva sample is taken from the patient's oropharynx. Results only take 15 minutes to appear. The test does not look for the genetic material of the virus—instead, it searches for its antigens. If the virus’ antigens are detected, a preliminary diagnosis can be made. The advantages of AG tests include their accessibility (for example, tests on the streets of Korea) and the ease of sampling biomaterials.
Accuracy: 80–90 percent
When to get tested?
Tests will be most reliable on the 5th or 6th day after the onset of the disease.
Serological antibody test
IgM or IgG antibodies are produced in response to contact with the virus. A drop of blood is required for the test. In the laboratory, information can be extracted about the antibodies and their quantity.
There is also an option for express testing, where a drop of blood is placed on a special cartridge. Reporting the results is simple and resembles a pregnancy test. If no antibodies are detected, one strip is shown on the device. If antibodies exist in the blood, two or three strips are shown.
Antibodies of the IgM class appear in the acute phase of the disease—it means that you have had an infection recently or are sick now.
IgG antibodies are produced 2–4 weeks after the disease and confirm that you overcame the disease and the immune system knows how to fight it.
Accuracy: 80–90 percent
The sensitivity and specificity of rapid tests vary from manufacturer to manufacturer.
When to get tested?
3–4 weeks after the onset of symptoms.
