Tests and diagnostics for Covid-19.

2021-06-04 10:21 PM

Subjects who need to be tested for Covid-19. People who need to be tested for Covid-19 are those who have at least one of the symptoms of acute respiratory infection caused by the SARS-CoV-2 virus, such as fever, cough, shortness of breath, sore throat, pneumonia, and one of the following epidemiological factors:

Having close contact (within 2 meters) with a person infected with Covid-19 or a person suspected of being infected with Covid-19, including people living in the same house, in the same office, traveling, working, sitting in the same row, and in front of them. behind 2 rows of seats on vehicles,…

Returning from “epidemic areas” recorded by WHO with Covid-19 cases within 14 days of entry (centralized isolation).

Return from epidemic areas within 14 days before the onset of symptoms.

Covid-19 patient during treatment as directed by a doctor/investigator/medical agency.

If you are among the subjects that are susceptible to Covid-19 above, you should immediately contact a health facility to be tested for Covid-19 soon.

Test Molecular test  

Antibody test

Definition

Real-time molecular biology test RT-PCR is a test method to determine the presence of viruses through the detection of the genetic material of the SARS-CoV-2 virus, which is a highly accurate method. According to CDC recommendations, the real-time RT-PCR test is the "gold standard" for diagnosing Covid-19.

 

An antibody test (serology) is a blood test that looks for the virus indirectly through the determination of antibodies in the blood. Antibodies are special proteins (IgM, IgG) that the body produces to fight infections. Normally, after an infection, it takes a while for the body to produce detectable antibodies in the blood. Performing the test can effectively detect people who have been infected with the virus before. However, it is not very effective in detecting new infections.

Procedure for taking samples for testing

Step 1: Prepare before sampling. Healthcare workers performing sampling should ensure biosafety principles for infectious diseases, including:
Wear the right protective gear and the right way.
Wear N95 respirator and helmet, goggles, face shield.
Wear 2 layers of medical gloves.
Perform disinfection and do not wear protective gear out of the sampling area.


Step 2: Take the specimen. Medical staff taking samples include:

– Take 3 – 5 ml of blood into the EDTA anticoagulation tube.

– Respiratory fluid: Use a sampling stick to perform upper and lower respiratory tract samples:

Upper respiratory tract fluid: Throat fluid, nasopharyngeal fluid, throat rinse.
Lower respiratory tract fluid: Sputum, alveolar fluid, endotracheal fluid, pleural fluid, lung tissue, bronchi, alveoli.
– Put the 2 sample strips that have been taken into the same tube of available virus transport medium.

Step 3: Preserve the sample. Once the sample is collected, the specimen should be sent to the laboratory as soon as possible.

Samples are stored at 2 – 8oC and transported to the laboratory 48 hours before sampling.
Samples are stored immediately at -70°C if transit time is expected to exceed 48 hours.
Do not store samples at -20°C or in the freezer compartment.
Whole blood samples can be stored for up to 5 days at 2-8°C.

Step 4: Pack and transport samples to the laboratory.

Tighten specimen type cap and cover with paraffin paper, cover each specimen type with blotting paper.
Place the sample in the sample carrier bag.
Cover the transport bag with absorbent paper, cotton soaked in water containing disinfectant (Cloramin B...). Then place the specimen pack in the second plastic bag and tie it tightly.
Close the specimen collection slips into the final plastic bag, tie it tightly and transfer it to a cold thermos, with the logo of biological specimens painted on the outside, and then proceed to transport.

 

Currently, there are two techniques for detecting antibodies:
ELISA technique helps to quantify the concentration of IgM and IgG antibodies in the blood, on average it takes 1-5 hours to get the result of antibody concentration in the blood.
The immunochromatographic technique (rapid test or rapid test): qualitative antibody, similar to the pregnancy test. This technique is simple, low cost, fast results. It only takes 15-20 minutes to have results with or without antibodies.

Result time

Real-time RT-PCR tests can give results in about 4-6 hours in the laboratory. However, it takes about 1 day to return the results. Results can help doctors predict disease progression, as well as evaluate the effectiveness of therapy.  

Faster with results in just 15-20 minutes.

Number of tests to get accurate results

How many tests are needed if the first test is NEGATIVE so that it can be said that the person is not infected or is “virus-free”. This is quite difficult, needs more research and updates for diagnosis, treatment, and surveillance guidelines at health facilities and in the community depending on the actual situation in the country, region, territory, and each locality.  

With antibody detection tests such as the rapid test, the test results are preliminary and screening only. The main purpose of this test is early detection of suspected cases, medical isolation if necessary. In many cases, patients who are tested negative for 2-3 times can still have the disease. In contrast, when the sample is taken between days 5 and 6, the positive rate is higher if the person already has the disease.

Meaning of results

The test can detect cases of SARS-CoV-2 infection at the end of the incubation period (1-2 days before the first symptoms) and the full-blown disease.
- Positive result: the test subject is determined to be infected with the virus and has the ability to spread and transmit the virus to others.
- Negative result: the subject was determined not to have SARS-CoV-2 virus at the time of sampling.
 

- A positive test result shows that you have antibodies from infection with the virus that causes Covid-19. However, there is still the possibility that that positive test result is a PASSIVE POSITIVE. After that, it is necessary to take samples from the pharynx, pharynx, and sputum to perform a confirmatory test for Covid-19. At the same time, conduct medical isolation of the patient.
- Negative result: subject was not infected with the SARS-CoV-2 virus at the time of sample collection. However, this test has a HIGH rate of PASSION, with about half of NEGATIVE results being incorrect.

However, testers continue to monitor their health status and isolate for 14 days. The rapid test can be performed again after 5-7 days.