Medichealthy Screening and Gold Standard Examinations to Diagnose COVID-19 - Medichealthy Screening and Gold Standard Examinations to Diagnose COVID-19

Screening and Gold Standard Examinations to Diagnose COVID-19

Rapid test for coronavirus screening is needed, considering that the spread of this disease is rapid. This rapid test or immunochromatography is beneficial because the results can come out faster, require lower costs, and can be performed in an environment with limited personnel and health facilities.
Screening and Gold Standard Examinations to Diagnose COVID-19
source Picture: https://www.dw.com/en/how-does-testing-for-the-coronavirus-work/a-52633616

Rapid tests as a coronavirus disease screening in 2019 (COVID-19) consists of rapid antibody tests and rapid antigen tests. Rapid tests are only an initial screening; the results of the examination must still be confirmed by Real-Time Reverse-Transcriptase Polymerase Chain Reaction (RT-PCR). 

In rapid antibody tests, the specimen is blood. Whereas the rapid antigen test, the specimen is taken from the oropharyngeal/nasopharyngeal swab and is only performed in a health service facility that has a biosafety cabinet.

Spread of COVID-19

At the end of 2019, a series of pneumonia cases with unknown causes appeared in Wuhan, China. After investigation, this virus is a new type of coronavirus called SARS-CoV-2. The increase in the number of COVID-19 cases took place quite quickly and spread between countries. The World Health Organization (WHO) finally established COVID-19 as a pandemic on March 11, 2020.

Based on the latest report from the European Center for Disease Prevention and Control on March 25, 2020, there were 421,413 confirmed cases of COVID-19 positive and as many as 18,810 deaths due to this virus.

The rapid spread of this disease makes several countries begin to implement rapid tests for the detection of coronavirus so that people under surveillance, patients under surveillance, and people in the transmission area can be immediately examined. If the results are positive later, isolation can be made immediately to break off the COVID-19 transmission chain.

Gold Standard Examination for COVID-19 

According to WHO, detecting new coronavirus ribonucleic acid / RNA (SARS-CoV-2) using the Real-Time Reverse-Transcriptase Polymerase Chain Reaction (RT-PCR) method, with specimens from sputum and throat swabs is the gold standard for COVID-19 examination. After doing the RT-PCR test, proceed with genome sequencing to confirm the diagnosis of COVID-19.

This test has high specificity but has low sensitivity, so the pulmonary CT scan is necessary to look for a picture of pneumonia due to COVID-19. RT-PCR test also has a high false-negative result if it often relies on the throat swab. Why? Because SARS-CoV-2 virus infection starts in the lungs, not in the upper respiratory tract. Moreover, this examination tool is not available in all health facilities because it requires expensive costs and trained personnel, as well as a long time in the process.

A study of 1070 specimens taken from 205 patients confirmed COVID-19, average 44-year-old patient, gave positive RT-PCR results on the highest bronchoalveolar lavage fluid specimens 93%, sputum 72%, nasal swabs 63%, swabs pharynx 32%), and blood 1%.

Rapid Test for Screening

The role of the rapid antibody test is to detect the presence of Immunoglobulin M / IgM and Immunoglobulin G / IgG antibodies against the SARS-CoV-2 virus from human blood samples. This test only takes 15 minutes and can detect COVID-19 infection in various stages of the disease.

IgM antibodies have an important role as the primary defense when a viral infection occurs, while the IgG response is to protect the body from infection by remembering viruses that have previously been exposed in the body.

Humoral Immune Response to Coronavirus SARS-CoV-2 Infection
In humoral immunity, what plays a role is B lymphocytes or B cells derived from stem cells. The primary function of humoral immunity is defending the body against bacterial, viral infections, and neutralize toxins.

The entry of foreign matter stimulates B cells to produce antibodies. Th2 cells also have a contribution to this immunity. T helper 2 cells produce Interleukin (IL) IL-4, IL-5, IL-6, which stimulate B cells to produce immunoglobulins, suppress the work of monocytes/macrophages and cellular immune responses.

Immunoglobulin is formed by plasma cells derived from B cell proliferation due to contact with antigens. Humoral immune response mechanisms are currently being investigated for SARS-CoV-2 infection. In one study, the median duration of detection of IgM and IgA antibodies was 5 days, while the median duration of detection of IgG was 14 days. This mechanism is the basis that the detection of immunoglobulins may be used as a coronavirus screening tool.

Confidence Levels of Rapid Test
In detecting various pathogens, there are several order levels of confidence (confidence level), the highest level of confidence is the culture test. Followed by molecular examination (DNA and RNA), antigen examination, and the lowest level is the antibodies (IgM and IgG as antipathogenic) test.

Even though the lowest level, the rapid test can still be used as an initial screening of COVID-19 before proceeding to an examination with a higher level of confidence, namely the RT-PCR examination. At date, the culture examination has not been performed for COVID-19.

Rapid Test Methodology for Corona Virus Screening

  • The coronavirus antibody rapid test cartridge consists of 5 parts, namely plastic backing, sample pad, conjugate pad, absorbent pad, and NC membrane.
  • Preparations that must be made on the cartridge before use are NC membranes attached to the plastic backing layer for secure handling.
  • Anti-human-IgM, anti-human-IgG, and anti-rabbit-IgG are placed in a row on the M, G, and C (control) lines on the rapid test cartridge.
  • The conjugate pad was sprayed with a mixture of AuNP-COVID-19 recombinant antigen conjugate and AuNP-rabbit-IgG. Previously, AuNP-COVID-19 recombinant antigen conjugate was made by mixing SARS-CoV-2 virus recombinant protein that had been dissolved into a mixture of AuNP colloids and borate buffer and then purified. A requires a specimen volume of about 10 microliters of serum/plasma or 20 microliters for whole blood. A sample pad was prepared with bovine serum albumin (BSA) (3%, w / v) and Tween-20 (0.5%, w / v).


Rapid antibody tests can use serum/plasma/whole blood specimens. From studies suggesting the consistency for each specimen is 100 percent. This test requires a specimen volume of about 10 microliters of serum/plasm or 20 microliters for whole blood. The specimen is placed on the sample pad then followed by adding 2-3 drops of buffer solution and the results within 15 minutes.

Interpretation of Rapid Test for Coronavirus Screening

A total of three lines are in the rapid test cartridge. The control line (C) turns red when the specimen sample has flowed through the cartridge.
  • Turning red test line in the M and G areas shows the presence of anti-SARS-CoV-2 IgM and anti-SARS-CoV-2 IgG. If only the control line (C) which is showing red, it means that the sample is negative 
  • If the M or G line or both lines turn red, it shows positive, and then it needs to be confirmed by RT-PCR examination.
  • If the control lines are not red, the test results are invalid, then need to do check again using another cartridge.


Specificity and sensitivity of Rapid Test in Detecting Coronavirus

According to WHO, rapid tests for COVID-19 screening still need to be further evaluated and cannot be used as a diagnostic tool. So far, there has only been one study that examined rapid tests for COVID-19. In that study, related to a rapid test for COVID-19 on 397 blood samples from COVID-19 positive patients, a sensitivity of 88.66% and a specificity of 90.63% were obtained. However, this examination still allows for false-negative and false-positive results.

Causes of false-negative results :
  • Low antibody concentrations, so if IgG and IgM levels are below the detection limit of the rapid test, the results can be negative
  • Differences in immune response, each individual in the production of antibodies, for example in immunocompromised patients who have impaired antibody formation
  • IgM antibodies will decrease or even disappear after 2 weeks


Causes of false-positive results:
  • The possibility of cross-reactive (cross-reactive) with other types of coronaviruses
  • History of being infected by a coronavirus that was not SARS-CoV-2 viruses in the past


Advantages and Disadvantages of Rapid Test Examination

The rapid test for COVID-19 screening has several advantages. When compared with RT-PCR, the rapid test saves time and does not require many pieces of equipment, this examination is easier to do and only requires a short training. The examination only requires a little blood from the fingertips because it is as good as blood from a vein. This allows inspections to be carried out in beds, clinics, laboratories, and even crowded centers such as airports and train stations.

Another advantage of the rapid test for COVID-19 is its ability to detect IgG and IgM antibodies in the asymptomatic SARS-CoV-2 carrier, so it is useful for controlling the spread of COVID-19. Moreover, the rapid test can detect IgM and IgG simultaneously, so that this examination can be performed as a diagnostic and monitoring tool during therapy.

The disadvantage of the rapid test for COVID-19 is this test cannot confirm the presence of the SARS-CoV-2 virus, but only provides information on the immune response to infection. However, the combination of rapid tests with RT-PCR can enable a more accurate diagnosis COVID-19.

Conclusion

Rapid testing can be an initial screening method for coronavirus. Although the rapid test is not as accurate as of the RT-PCR examination, it can measure the extent of the spread of COVID-19 infection. Rapid tests can help show exposure to infection, especially in suspected cases, so that it can be used for epidemiological studies and further research.

Since this rapid test allows for false positive and false negative results, positive results should still be confirmed by RT-PCR tests, whereas ODP / PDP with negative results must be retested after 7 days. Further research is still needed relating to rapid tests for coronavirus screening.

author: dr. Nurul Falah 


References
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